ancient inland dunes of northern europe

Ancient Inland Dunes of Northern and Middle EuropeAuthor(s): Ivar HögbomSource: Geografiska Annaler, Vol. 5 (1923), pp. 113-243Published by: Blackwell Publishing on behalf of Swedish Society for Anthropology and GeographyStable URL: http://www.jstor.org/stable/519659Accessed: 14/12/2010 18:27

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ANCIENT INLAND DUNES OF NORTHERN AND MIDDLE EUROPE

BY IVAR HOGBOM.

Introduction.

T he present work has a twofold object: first, to present a survey of the ancient North and Middle European inland dunes,' their regional distribution and their morphology; secondly, to inquire how far our views on

the postglacial climatic development may be affected by such an exposition. Several scientists have formerly been occupied with these problems, but hardly anyone has built upon a combination of personal or foreign observations from more than a limited area. As the dunes show a rather capricious morphology, and as after only local studies they invite to widely different interpretations of their genesis, the literature of the subject displays a rich assortment of contra-

dictory statements and theories. Besides, even the regional aspect of the dune-

problem has been rather neglected, and the dunes have commonly been regarded as formations of secondary importance only, as a lusus naturae of no very general geological interest. This ought to be otherwise, as the dunes in one respect occupy a special position, since they indicate better than other postglacial formations that particular climatic conditions have prevailed at the time of their com-

ing into existence. Our knowledge about the postglacial climatic development in Northern Europe

is founded mainly on examinations of peat-bogs and plant-geographical investigations, and as the results in many points do not wholly agree, they have not been

universally accepted. The purely geological researches have yielded fewer contributions to the climatological discussion, so that every new possibility offered of a geological controlling on any point of the theories otherwise arrived at, is of particular interest.

The Swedish dunes have been the chief object of my studies, and my original purpose was only to review the publications of foreign geologists on the Middle

European dune-districts. As the work proceeded, however, I found, that the Swedish dunes were rather easily disposed of, and that, as I have mentioned,

1 I prefer to use the term ,ancient, instead of ,fossil,, the latter term should rather be attached only to dunes of older formations, the existence of which may be observed in some sand-stones.

8 Geografiska Annaler 1923.

114 IVARR HOGBOM

the foreign literature on the subject was so heterogeneous, and contained so

many conflicting statements, that a mere summary could not give a clear picture of the dunes of the continent and their genetic problems. I have therefore, both

by investigations of my own in the German and Hungarian dune-districts and by a critical examination of available sources, tried to produce a survey of the entire dune-problem of Northern and Middle Europe. Also I believe that the Swedish dunes, the age of which may be considered as determined beyond doubt, may afford enlarged possibilities for judging the questions associated with the Middle European dune-formations.

The general climatological questions I have reserved for a separate chapter at the end of the work and devoted the first and chief part to the descriptive and

morphological aspects, following the dunes regionally from the Scandinavian countries southwards. On. account of the many different theories existing in regard to the general conditions for the development of dunes and the mechanics of

dune-drifting, however, I have considered it necessary to treat these questions in a special first chapter, as they are not unimportant for the comprehension of the ancient dunes.

It is an agreeable duty to me here to express my most sincere thanks to my teacher and father Prof. A. G. Hogbom, who some ten years ago proposed to me to take up the question of the dunes in Dalarna, and who later on, when I took up the inquiry anew and extended it to other dune-regions, has furthered

my studies by his good advice. I am also indebted to Prof. Gunnar Andersson, who made me overcome the

hesitation I felt before entering upon the investigation here presented, and who has afterwards given me many hints of value for its publication.

I wish to express my thanks to the chief and officials of the Prussian Geologi- cal Survey for courtesy shown in different ways, and especially to Prof. P. G. Krause for his kindness even in accompanying me on some excursions to the dune-fields.

In Hungary Prof. E. v. Cholnoky not only helped me by facilitating my excursions, but also showed his interest in my studies by discussing with me many problems connected with the dunes. To my friend Dr. A. K&z of Budapest, who

accompanied me on my travels in different parts of Hungary, I am particularly indebted for the kind assistance he thus gave me during a never to be forgotten fortnight.

Finally, I beg to thank Red. V. Hammarling and Lector C. S. Fearenside, who have corrected my manuscript and proofs from a linguistic point of view, and Miss Astrid Starup, who has drawn the figures after my pencil-sketches.

ANCIENT INLAND DUNES OF EUROPE 115

CHAPTER I.

Dune-formation and Dune-morphology.

Even regarding the most fundamental characteristics of dunes, their origin and

development, no general theories have as yet been unanimously adopted by the

geologists; authority stands against authority on almost every important point. This is perhaps mostly due to the fact that dunes have usually been regarded as formations of no essential interest and thus have often been treated more or less superficially even by those scientists who have had the best opportunities of

making detailed observations of their various morphology in recent deserts. It seems thus necessary to commence even a study on ancient dune-fields with a

survey of those problems which should otherwise properly be solved by special investigations in actual dune-regions.

In several respects I feel bound to object to the theories and explanations of those geologists who have previously dealt with the problems of the dunes. Thus, I find it appropriate at this place to begin with a critical review regarding the literature on the mechanics of dune-formation, adding to this some experiences and remarks of my own. Naturally, I must confine myself to mentioning only those authors who have made the most important contributions to the dune-

question in general or to the problems directly or indirectly bearing upon the

interpretation of the history of ancient fields.

Dunes and Wave-movement.

To begin with, so much confusion has been caused by wrongly interpreting dunes as sand-waves that it is not possible to pass over the question what sort of formations dunes really are, as seen from a mechanical point of view. On the other hand, the aerodynamic processes calling forth dune-building, are partly very complicated and fall within a purely physical domain of science, so that a

complete treatment of these phenomena cannot be expected in a geological study like the present paper. Though aware of this limitation, I will try to point out some facts of importance for the following geological and climatological discussion of the ancient dune-formations.

In a series of papers Helmholtz (1888-1889) has shown that, when gaseous or liquid media of different specific gravity are moving with different velocity, wave-formation will take place at the contact plane. The wave-movement, which Helmholtz mathematically analyzed, is due to the labile pressure conditions on the contact-plane called forth by the relative movement on both sides of it. The

116 IVAR HOGBOM

wave-movement, when fully developed, changes this labile pressure situation into a stable one. Certain dimensions of the waves as to velocity, amplitude, etc.

correspond to a certain relative movement of the two media and to their physical properties. Through the studies of Helmholtz the wave-movement is thus

proved to be the necessary approaching to a stable situation from an unstable one, and formerly proposed explanations of waves as originated by supposed irregular wind-pushes etc. are needed no longer.

Helmholtz himself makes no application of his theories to dune-formation, but some authors on dunes have later referred to them, usually without taking into consideration the fact that Helmholtz confined himself to treating only real wave- formation, that is such as takes place in plastic media, gaseous or fluid.

A scientist, who in my opinion, has given one of the most impressive suggestions as to the principles of dune-formation is Baschin (1899 p. 419), who in the dunes as well as in the ripple-marks sees >Die Tendenz zur Bildung einer Helm- holtz'schen Wellenfliche>). By this formulation and by the reasoning upon which it is based he makes it clear that he recognizes the restricted applicability of the theories of Helmholtz to the dune-problem. However, there are other objections to be raised against the opinion thus expressed in what regards its applicability to dunes; and I shall later have an opportunity to return to the Baschin paper and to the questions here touched upon.

In his work on the properties of the snow-cover in Lapland, Hamberg (1907, p. 7), reviewing the studies of Helmholtz and Baschin, agrees with the latter in

regarding the ripple-marks and the dunes as originated by pressure-conditions on the surface, similar to those which cause water-waves. However, he lays particular stress upon the differences due to the different kinds of material between air- waves and water-waves on the one hand and sand-dunes on the other.

As is shown by Hamberg's studies, the formation of snow-dunes is far more

complicated than that of sand-dunes on account of the varying physical properties of snow under the influence of temperature and packing etc. Regular systems of snow-dunes are therefore very seldom to be observed.

Certain authors, however, have given no consideration at all to the fundamental difference between waves and dunes. Solger (19io, p. 26), for instance, who has

specially treated the problem of the ancient inland dunes in Germany, tries in

every respect to adapt the consequences of the wave-theory to dunes. He neglects 1he difference between the intermittent leaping movement of the sand-

particles, which are seized by the wind on the wind-side and then embedded within the dune on the lee-side, and on the other hand the continuous movements of the particles of a fluid, following the circular or elliptical orbits which characterize the real wave-movement. Another theoretically important difference between wave-movement and the movement of the sand in dunes is


constituted by the circumstance that in the latter case there is a real removal of material in one direction which is quite incompatible with wave-movement as

physically defined. This simple fact that the sand moves only on the surface but not beneath it, that sand is no plastic medium, however, has been overlooked by a number of authors, and Solger expressly starts from the premise that ))Der leicht bewegliche Sand verhalt sich ahnlich wie eine Fliissigkeit>).

The above may suffice for the statement that dunes may be sand-waves in a more or less poetical sense of the word, but that the movement of the sand in a dune-field is of quite different character from the wave-movement of the particles in a fluid. How far, on the other hand, the wave-like sand-forms can be re-

garded as caused by air-waves will be elucidated by the reasoning in the sequel. The evident difference between real wave-movement and the dune-movement

has, however, brought even some of the scientists who accept the wave-theory to feel that something is wrong, and to seek for further special reasons for the dune-formation which certainly they would not try to apply to water-waves.

There are two theories on the origin of dunes, both based on false premises or misunderstandings, but often adopted without criticism and objection even in recent and otherwise valuable works.

Theory of Ripple-marks as embryonic Dunes.

What has been said above regarding dunes and wave-movement can evidently in many respects be applied also to the mechanics of ripple-marks, and the

theory of the ripple-marks as embryonic dunes, capable of growing bigger until the dimensions of dunes are attained, is most closely connected with the apprehension of dunes as sand-waves.

The theory is adopted by some writers of hand-books, e. g. Haug (I, 1907). Kayser (1918) reviews it, without taking position for or against.

The foremost defender of this theory is perhaps Baschin (1899, 1903) who, as cited above, regards ripple-marks and dunes only as different phases of the same phenomenon, viz. the tendency to the formation of a Helmholtz wave-surface. Cornish in his latest work (1914, pp. 57, 88) regards the irregularity in the intensity of the wind as the cause of dune-formation, whilst he thinks the

ripple-marks are due to eddying processes and to the selective picking up by the wind of grains of different dimensions. In both cases he looks upon the forms as true waves. In his earlier publications, however, he speaks of ripple- marks as embryonic dunes. Eventually Exner (1920, 1921) arrives at the last- mentioned opinion, basing on experimental studies, which will be criticized below.

Cholnoky (1902, p. I 28), on the other hand, states that the ripple-marks, being characterized by determinate dimensions, are in no way to be regarded as em-

bryonic dunes and that there is no transition between dunes and ripplemarks.

118 IVAR HO0GBOM

Hedin (1905, II, p. 412) supports the theory of ripple-marks as embryonic dunes and treats both forms as due to a particular wave-movemrnent in the sand, characterized i. a. by the triangular paths of the grains.

For my own part I am absolutely convinced of the validity of Cholnoky's observations. At Skagen, for instance, I have watched the behaviour of ripple- marks for a couple of hours when the wind, while blowing always from the same direction, was very variable as to intensity. Sometimes the wind was too faint to move the sand-grains at all; sometimes they were rolled over the wind- sides of the ripple-marks and embedded on the lee-sides; but when the wind was

strongest, there was a continual transportation, the grains gliding in the wind- direction even down the lee-sides and across the interstices between the ripples, thus following the sinuous curve of the surface. The distances between the

ridges of the ripple-marks were about 5 cm, and the velocity of the ripple-marks about 2.5 cm per minute, when the wind was blowing at its hardest; the velocity of the individual grains was very irregular and impossible to measure. There were, however, no changes as to the dimensions of the ripple-marks, although the wind was so varying, and no joining of different ridges was to be noticed even during the strongest pushes of the wind. In order to verify the last-mentioned fact I had my attention specially fixed on the junctures between some

ridges, regarding which no regular displacement in transversal direction took

place. The literature dealing with ripple-marks is rather voluminous. A review of

the many hypotheses which have been set forth on their origin and development would, however, be of small importance for the problems of the ancient dunes. For further reference I mention the studies of Bertololy (1894) and Kindle (1917).

The mathematical analysis of the surely unstable pressure conditions on a sand- surface, when the wind is blowing over it, has not yet been carried out, and perhaps this problem is too complicated to be generally solved. Anyhow, it is astonish-

ing that those who employ a more or less modified wave-theory to account for the origin of dunes, have not made any attempt to ascertain how far the dimensions of dunes actually conform to this theory. Because the difference in specific gravity between two air-layers is so much less than between air and water, the air-waves observable as ripple-clouds are about io,ooo times greater than the water-waves (Wegener 1906, 19i11, p. 151). Under such circumstances the question lies near at hand, which dimensions would be characteristic of >sand-waves> because of the greater specific gravity of sand, the physical difference between sand and the plastic media in other respects not taken into account.

Wien_ (894, 1895)r has deduced the following formula for the calculation of 1 Cfr also Wegener, 1906, 19I I.


wave-lengths on condition that the height of the waves is very small compared with the length:

g (p,1--p2) 2;z a22o2 +-al121-g

In this formula ? represents the wave-length, P2 the density of the upper layer, or that of the lower layer, a2 the velocity of the upper, and and a, the velocity of the lower layer relatively to the velocity of the waves, and g the acceleration.

In the case of sub-aerial >sand-waves>> here in question, the terms a, p1 and

may be neglected. The equation thus gives the following value for 2. 2/

With a specific gravity for the sand of 2, and for air of 0.oo0012, this gives a wave-length corresponding to winds of 5, Io, and 15 m/sec. of respectively:

A'5 -= I cm; 2io = 4 cm; A15 -9

cm.

From this it is clear that the sub-aerial sand-forms, which are to be considered as the nearest genetical parallels to waves in the plastic media, are the ripple-marks, as the dunes have quite other dimensions'. Using the formulation of Baschin, cited above, I should thus regard only the ripple- marks, but not the dunes, as the product of the tendency to the forming of a wave-surface at the contact between the plastic medium air and the non-plastic medium sand. Perhaps it will also prove possible to explain why the ripple- marks seem to keep their dimensions independently of at least short variations in the intensity of the wind, when full regard is taken to the physical properties of sand and the consequent modifications in the validity of the above-mentioned formula. This, however, falling outside the limits of the present study, I have confined myself to the above remarks, in order to prove the impossibility of

regarding dunes as surface-forms in any respect connected with wave-movement. In a preliminary note Cholnoky (1902, p. 128) has also expressed the opinion

that a connection exists between ripple-marks and waves, but that regarding the 1 For sub-aqueous

,sand-waves, the same equation (a,2pi neglected) gives the following wave-lengths,

corresponding to water-currents of 0.2, 0.5, and I m/sec.:

20.2 = 3 cm; 20.5 = 16 cm; 2i

= 64 cm.

In fact even these dimensions do not contradict actual observations in nature, if due consideration is taken to the difference between the marks produced e. g. by the alternating currents of the swell, and the current-marks produced by a continuous current, e. g. on the bottom of a river or a creek.

Naturally the equation is not applicable to the development of the first-mentioned forms. Neither the ciirrent-marks nor the aeolian ripple-marks can of course be expected to show an absolute accordance to the dimensions calculated from the formula, as it pays no regard to the special physical properties of the sand. It is, however, striking that in both cases there is a good accordance as to the order of dimensions.

120 IVAR HO0GBOM

latter the only factor determining the dimensions is the friction between the air and the sand-surface.

Exner (1920), on the other hand, has lately published a new hypothesis on the wave-movement between two media and its consequences in regard to dunes.

According to the equation set forth by Exner, the amplitude and the length of the waves (or dunes) are continually increasing during their wandering from the

starting-point, thus passing from the stage of ripple-marks to that of dunes. The dimensions of a wave would thus be a function, not only of the physical properties of the two media and their relative velocity, but also of the distance

passed from the starting-point. Exner bases this opinion on laboratory experiments, and his equation is not

the result of a dynamic theory, but constructed in order to suit the experimental result. Any incompleteness or misinterpretation of the experimental arrangements are thus of decisive ,consequences for the whole theory. In fact, there are objections in that respect to be made which Exner himself admits, when describing the apparatus and the results obtained. Through a box-like tube he has blown air with a certain constant velocity over the sand-covered

bottom, and has ascertained that the dimensions of the ripple-marks increase from the entrance up to a certain dimension. The cessation at this point he ascribes to the small dimensions of the experimental apparatus, and therefore he reckons only with the increasing dimensions at the beginning. As, however, the maximum dimensions obtained in the experimental box seem to correspond to those usually attained by ripple-marks in nature, the experiment does not contradict the observations made by Cholnoky, myself, and others, that there are no transitional stages between ripple-marks and dunes.

As far as I can see, Exner's hypothesis cannot, as Exner himself supposes, be applied to dunes, but the experimental results may be of some importance for the interpretation of the ripple-marks.

I have already pointed out the principal difference between ripple-marks and

dunes, and besides, there can be found no evidence, e. g. in the great deserts, that the dimensions of the dunes are continually increasing in the manner shown

by Exner's equation and experiments on a small scale. If it is often possible to observe that dunes grow bigger while wandering, this is quite another phenomenon, due to a purely accumulative process.

Theory of )the small Obstacles>.

According to the other theory on the formation of dunes, these originate from minute aggregations of sand, caused by a stone, a plant, or another prominence


presenting a relative resting-place for the wind-driven sand. Once begun, such an accidental heap is supposed to deviate the wind further, thus offering an

ever-increasing shelter for the accumulation even after the formed dune has begun its wandering and has long ago left its original rooting place. For the sake of

brevity, this theory may be termed > the theory of the small obstacles>>. This theory on the origin of dunes has been adopted by many writers of hand-

books; Penck (1894, I.), Ramsay (1912), Pirsson and Schuchert (4915), Neumayr- Suess (1920), and others, whilst e. g. Kayser (1918) already finds it antiquated.

Sokol6w (1894, p. 63, 74) gives a long description of the building up of dunes

according to this theory. He regards especially some xerophilous plants as the

ordinary cause of dune-accumulation and describes the transitional stages between the primary heaps and the fully developed barchans. Particularly he emphasizes the essential difference between the obstacles presented by plants, which are per- meable to the wind, and those offered by stones etc., and points out the ensuing dissimilarity in sand-accumulation. Yet more important seems to me the continued cooperation of the xerophilous plants during the process of sand-accumulation, the plants being forced to grow up higher, in order to reach the air, and new shoots taking possession of the fresh sand. Thus the plants may be a means of

continually keeping and binding the arriving sand. In fact most examples of the influence of small hindrances as originating dunes observed in nature refer to this consequence of the action of plants. Also another quality of the sand-

heaps accumulated because of the fixing power of vegetation should be laid more stress upon than is usually done. By an extraordinary strong wind the

vegetation may be swept away, and in this case the transitional stage between the primary heap and the wandering dune is easily understood. This transition, on the other hand, presents some difficulties for an explanation of the origin of dunes, which would have arisen out of sand-accumulation behind solid obstacles.

Although it seems undeniable that in some cases >)the small obstacles>, and

specially the xerophilous plants under conditions mentioned above, may give rise to dune-formation, there is no doubt that in general other factors are to be reckoned with. Some authors have also recognized the untenability of the theory as a general explanation of the origin of dunes. So e. g. Hedin (1905, II, p.

4o10), with a good sense of proportions, denies the possibility of seeking the

origin of the numberless great dunes of the Asian deserts in small futile ob-

stacles, and thinks that, independently of these, some more general laws must

regulate the dune-building. >For my own part, I believes>, Hedin says, >that, if the masses of sand now in the desert Tschertschen were to be spread out per- fectly evenly over the desert in a layer some 3o m thick, the sand would after a certain lapse of time be rearranged by the wind in dune-accumulations pre-

122 IVAR HO0GB0OM

cisely similar to those that now exist.>) It seems also too great an absurdity to think that the now quite barren great dunes in big deserts should owe their

origin to occasional tufts or other obstacles of similar dimensions dating from

past centuries. Walther (1912, p. 261) seems to believe in the theory of >the small obstacles>,

but mentions also the possibility of wave-movements in the air as originating dunes: >Der Beginn der Diinenbildung ist ein flacher Sandhaufen von beliebiger Gestalt. Die Entstehung desselben kann veranlasst werden durch unbedeutende

Rauhigkeiten des Bodens, kleine Steinchen oder Grashalme, vielleicht sogar durch die wellenf6rmige Bewegung der Luftst6sse. Jedenfalls ist seine Gestalt sehr wechselnd und regellos.>

Jentzsch (19o00, p. 50) does not regard any obstacles in the form of plants etc. as necessary conditions for dune-formation. In a reasoning, not quite easy to

follow, he tries to show that the dunes primarily are caused by irregularities in the direction of the sand-driving wind. These, he supposes, cause a disturbance of the aeolic equilibrium, which otherwise ought to be the result of a constant wind, and which would

be. characterized by an even regional assorting of the

material, from the coarsest to the finest in the direction of the wind. Jentzsch treats dunes and ripple-marks differently although he speaks of beginning dunes

hardly one centimeter high; the essential difference is somehow made out to be that dunes are produced by eddies with a vertical axis, and ripple-marks by eddies with a horizontal axis. As far as I have seen, Jentzsch has found no

support for these distinctions amongst other scientists. At some places, and very beautifully at Skagen in Denmark, I have myself

had an opportunity of observing dunes in statu nascenti, where on level gravel ground sand-sheets of elongated or sometimes barchan-like forms were deposited absolutely independently of any such obstacles. I was there when the westerly wind had changed to a more southwesterly one blowing out clouds of sand from the irregular dunes

(>klitter,) on to the bare, some hundred meters broad, plane

sea-shore. The sand-sheets thus formed, which are only one or two decimeters thick, bear no similarity to the small, rather prominent sand-heaps behind tufts or

plants; there are no transitional stages between the two, but undoubtedly the former ones represent the regular beginning of dune-accumulation. That in this case the beginning dunes mostly were of a somewhat longitudinal shape is to be ascribed to the winds radiating from the narrow openings between the

>,klitters>). A broader development of the sand-depositions at some distance from these gaps was also to be noticed.

The above-mentioned instance seems to me to give a good illustration, on a small scale, of the usual cause of dune-formation according to the opinion, which I am advocating on following pages in this treatise, namely, that there are irre-


gularities, quite distinct from the >small obstacles>, which are always present in nature and which locally lessen or strengthen the transporting power of the wind and thus ultimately are the initial causes of dune-formation. It is, however, exceptional that they should be of the marked character shown at the >klitters> of Skagen.

The shield-formed or the laterally extended Sand-accumulations as initial Dunes.

From what is related above it is evident that neither the theory of the >small obstacles> nor the observation of the behaviour and the development of ripple- marks gives the clue to the general cause of dune-formation.

The instance just mentioned from Skagen and similar observations seem, however, to illustrate quite clearly the origin of dunes. The fact that the first

deposits of sand are spread out like a shield contradicts both the theories mentioned. The influence of smaller obstacles, locally checking the wind, upon the deposition of the wind-driven sand, gives quite different results, as all students of aeolian sand-accumulations have had the opportunity to observe. The

depositions caused by stones or tufts etc. are always of an in the wind-direction

elongated, comparatively high tongue-form, in no way similar to the thin sheets, which have actually been observed developing to real dune-forms with the characteristic wind- and lee-side slopes. As the accumulation continues, the primary sand-shield gradually is transformed into a barchan. If the primary sand-sheet is laterally extended or if several sand-shields join each other, transversal dunes

develop. The slield-form of the primary accumulation is also mentioned by some

authors, e. g. by Davis and Braun (1911, p. 244). Walther also (1912, p. 262),

speaks of the shield-form of the primary dune (>>schildf6rmige Urdiine>>) without

recognizing its incompatibility with his apprehension of the small obstacles as

initiating the accumulations. The causes of the spreading out of these sand- shields are not the small obstacles in the meaning of that term usually adopted and should be further inquired into.

If a wind is blowing over an absolutely even sand-plain, the only result ought to be ripple-marks, according to the tendency to produce a wave-surface already mentioned. Such ideal conditions, however, are not met with in nature. When

entering the sand-plain, the wind has generally a vertical component, either because it comes from a higher or a lower foreland or from the lower surface of a river, a lake, or a sea. Also this circumstance gives to wind the power of deranging the supposed even distribution. Further any primary undulation of the sand-surface influences the wind in the same manner, and local wind-pushes also cause local deflation or inflation of the sand, thus producing irregularities on the sand-plain, if such caused by other agencies were not to be found. The transporting power

124 IVAR HOGBOM

of the wind is thus in nature never quite constant, and the result is an outspread accumulation over smaller or greater areas, where the power of the wind is smaller than on the surrounding field.

At first sight, however, this explanation of the initial heaping up of sand seems to contradict the regularity with which dunes usually are arranged within the fields. There are two possibilities to put a satisfactory interpretation upon this

phenomenon, each of which may be applied to a special type of dune-system. One of them is shown by the wandering away e. g. of a shore-dune, which leaves its original place and the possibilities thus offered for the formation of a

following dune. The development of such dune-systems is often described from

shore-regions, and needs no further comments at this place. It is, however, evident that in many cases this cannot account for the regular arrangement of dunes, especially within the great deserts. Obviously the dunes cannot have wandered for hundreds of kilometers keeping almost exactly the same height and the same interspace, at least if no automatically correcting factor is supposed to

regulate the wandering and to balance accumulation and deflation. As far as I have been able to find in studies dealing with dune-formation or

in hand-books of mechanics, no investigation has been made regarding the run-

ning of the stream-lines of the air, when the wind, blowing over a plane surface, passes a vertically erected obstacle. Usually it is assumed, without further ent-

ering upon the subject, that the stream-lines on the lee-side of the hindrance

asymptotically approach the surface, respectively its parallels. There are, however, many reasons which indicate that the process is far more complicated. Even the fact that the air, after having passed the obstacle, has a component downwards against the plain, must cause a rebounding, that is an elevation once more of the stream-lines, involving a weakening of the transporting power of.the wind at the surface of the ground at a certain distance from the lee-side of the obstacle. Thus an intensifying of the power of transportation of the wind must exist at a certain distance from the first hindrance or dune, followed by a place where the power is lessened, creating new possibilities for deposition of sand. A further reasoning on this line shows that a vertical obstacle for a wind blow-

ing over a -plain makes the stream-lines run sinuously, although naturally with

quickly decreasing amplitudes. The process reminds one in many respects of the depositions and excavations which take place in a meandering river. This

analogy is also pointed out by Exner (1921, p. 328). It is further very possible that more complicated eddying processes develop, comparable to those studied in water streaming about a body.' Such processes too may cause a varia-

1 Also these studies have not yet been advanced so far that they allow any strict comparisons, as they deal principally with the stream-lines enclosing a solid body moving in relation to the fluid, but not with the case.of a fluid streaming above a plain on which an obstacle is placed. The dynamic problem of the more complicated eddies is as yet not solved.


tion at certain points of the transporting power of the wind and thus be a means of explaining the regular arrangement of the dunes within the deserts. A general equalization regarding the heights of the dunes must further result from the

greater power of the wind at the highest dunes.

Although the above lines in no way pretend to give a full explanation of the

very complicated problems of the development of dune-systems, they may suffice to indicate that wave-like movements in the air may be the result of a hindrance once passed, and that further observations in nature or experiments and theoretical investigations, carried out on this line, may probably give the clue to a fuller

understanding of these hitherto unsolved problems.

The Dune-profile.

One of the most prominent features of a dune is the characteristic cross-section in the direction of the wind showing a gently ascending wind-side and a

steep lee-side. The former is usually curved, slowly ascending at the foot and

reaching a maximum steepness at the point of inflexion at about half of the

height, from where, with decreasing steepness, it reaches the top of the dune more or less tangentially and, in the case of barchans, passes it with a gentle slope down to the edge. It is this edge that should properly be regarded as the

boundary between wind- and lee-side, and not the highest point of the dune. The lee-side, on the other hand, shows in the profile an almost straight line with a

steepness up to the angle of rest for sand, or about 33--35'. This is the typical profile of the fully developed barchan, as is shown by the most careful measurements of Sokol6w (1894, p. 8o), Cholnoky (1902, p. I20), and others.

In transversal dunes the profile is usually somewhat modified in so far that the edge cuts off the wind-side before its curve reaches the highest point as

a b

Fig. I. Typical profiles of a barchan, b transversal dune.

described above or at least immediately after. In this case the section is approximately triangular (cfr e. g. the exact cross-section measured by Hedin, 1904, P1. 43).

These different types of dune-profiles are surely due to different conditions of accumulation or deflation not yet thoroughly investigated or explained.

The explanation of the difference in steepness between the wind- and the lee- sides of the dunes does not involve any great difficulties. Contrary to what

126 IVAR HOGBOM

can be said about almost every other question regarding dune-formation, there seems on this point to be a general agreement even about the principles. The

development may in short be said to be as follows. Because of the deviation of the stream-lines over a sand-heap, deflation is taking place on the side facing the wind; on the back-side, on the other hand, the lines are diverging from the

surface, and the moving sand falls down as soon as there is no supporting plane for it to move on. There are, however, also in this case some complications which should be mentioned, although they are of less importance for the development of the dune-profile. Especially when it is blowing hard, the sand-grains must have a considerable velocity when passing the edge, and do not fall quietly over it, but may be transported further through the air, not touching the ground before they reach a place where the wind is strong enough to drive them further. The result is

that, when a strong wind is blowing, there is a continual transportation of sand fol-

lowing more or less the sinuous current of the wind, without being embedded in the lee-sides of the dunes. This is in fact often observed in deserts; the sand flies from the tops or the edges of the dunes (cfr e. g. Walther, 1912, p. 271). It explains also why dunes have often been practically stationary although sand-storms are not infrequent in the region in question; thus there are instances known where for several years no change has been observed in the waterplaces of the caravans at the foot of a certain dune. The observation of Hedin (1904, I, p. 261) that loosely packed sand covers not only the lee-sides of the dunes but also often the nearest zone of the valleys, gives another evidence for the

way of sand-flight mentioned. As Walther (1912, p. 271) points out, the most formidable sand-storms are due

to irregular winds, interfering with the dune-system by attacking the loose and

steep lee-sides of the dunes.

Although of less immediate importance for the discussion of the ancient dunes, some further remarks on the mechanics of dune-drift may be allowed in this connection, in order to give a truer conception of the processes in question.

In the first place we might examine the most simple process, namely that of a wandering dune with a constant profile, that is without accumulation of more sand or deflation on thile lee-side. Furthermore, in order to simplify the

discussion, the section may be regarded as triangular. When the dune wanders a certain distance A, this means that a mass of sand,

in the diagram Fig. 2 represented by the strip AH, is detached from the wind- side and replaced on the lee-side as the broader strip BH. All the displaced sand has to pass the edge, whilst e. g. only half of it passes a point half-way up the wind-side. Thus the amount of sand which during a certain lapse of time

passes a certain point on the wind-side of the dune, is directly proportional to


the altitude of the point in question. Again, from the foot of the dune up to the top, the intensity of the wind must increase in some degree (naturally not

directly proportionally) to move the respective quantities of sand, if the profile is supposed not to alter during the wandering of the dune. These observanda seem to be of some importance as well for the understanding of the wanderings of the dunes as for the study of the ripple-marks on them. The track of a

AH

Fig. 2. Schematic profile of a dune in moving. The thin layer A-H is blown away from the wind-side and accumulated on the lee-side as

the thicker layer H-B.

sand-grain, in relation to the body of the dune, is thus a triangular one, the base of which varies in length from that of the base of the dune down to zero.

As all deposition was supposed to take place along the slope of the lee-side, the stratification in the dunes in this case shows a run parallel to the steep lee- side slope.

The dunes met with in nature have not an exactly triangular section which

implies some modifications in the above reasoning. These would, however, be too complicated to be followed up in this place. One consequence only, regarding the way of accumulation within a dune with a profile of the barchan type, may be illustrated. In this case accumulation takes place even on the space between the highest point of the dune and the edge. If any stratification could be observed, this in the part of the dune, lying above the altitude of the edge, would be gently declining in the direction of the wind.

The conditions prevailing, when the wind is driving sand from another dune or from the frontal plain against the wind-side of the dune in question, are more

complicated, as the accumulation may take place either on the wind-side, the lee-

side, or on both of them, chiefly depending upon the intensity of the wind. In the case of accumulation on the wind-side, the stratification shows the gentle slope against the wind characteristic of wind-sides.

From the above it is evident that, if from the stratification in the cutting of a dune any conclusion is to be drawn as to the direction of the winds which have caused it, one has first to make out whether it is a case of wind- or lee-side stratification. The difference in inclination between wind- and lee-side, however, is

128 IVAR HOGBOM

always so great that this meets with no difficulty. As a rule, it may be assumed that an inclination of less than say 150 corresponds to the wind-side, and

over I5' to the lee-side. If, therefore, in a cutting there is found both a steeper stratification declining to one side and one of gentle slope towards the other side, this may only mean that the dune-driving wind, coming from the latter direction, has been of varying intensity.

The stratification of the sand in dunes is often described as diagonal, though, so far as I know, there has been little consideration given to its origin. As a matter of fact, this diagonal stratification seems to be only the traces of overblown ripple-marks. That it does not, as a rule, directly reflect the intersections of the ripple-marks is of course due to the continual overblowing, which does not allow a fixation of a definite stage during the wandering of the ripple-marks. The process is, naturally, very complicated and difficult to follow in detail, especially as in nature we have to count with variable winds and, as a consequence, different conditions of accumulation. A similar diagonal stratification is also met with in some aqueous formations, where it is certainly to be considered as the traces of sub-aqueous ripple-marks; it is characteristic that the distances between the successive banks in this case are other than inaeolic depositions (Haug, 1907, p. 403). In the places where I have made observations, the distances between the supposed ripple-marks have also - as far as the indistinct diagonal stratification permits observation at all - corresponded to the dimensions typical of actual ripple-marks.

In this connection a question of great importance for the understanding of the

wanderings of dunes should be mentioned, namely regarding the possibility of deflation from the lee-side. If the lee-side has the slope of sand at angle of

rest, this must theoretically mean that an absolute calm is reigning on the lee- side. This is evidently not the case in nature. Either there is a backward eddy to be reckoned with, or the stream-lines of the wind follow the slope downwards, although diverging from each other. In the first case the wind operating against gravity would theoretically tend to produce a steeper lee-side; in the second case the wind, cooperating with gravity, would produce a more gentle slope, and the sand might even be transported further on the level ground. If there arose a combination of accumulation on the wind-side and deflation on the lee-side, the dune-form would move backwards, although naturally the sand would be trans-

ported with the wind. In fact this combination seems to be very probable when moderate winds are blowing, both because of the relatively greater influence of gravity in this case and also because eddies do not develop until a certain intensity of wind is attained. In a later chapter I shall also have an opportunity to mention actual observations in nature of dunes, showing the characteristic stratification of wind-side accumulation with the comparatively gentle wind-side slopes.


In good accordance with the brief description given above are the interesting calculations of Exner (1920) regarding the wanderings of dunes. They show, however, that even with the help of great approximation the problem involves too many factors, as yet unknown as to their relative importance, to allow a de- finitive mathematical treatment. Besides those pointed out by Exner himself, the influence of the eddies, earlier touched upon, might be mentioned, the general mechanics of which are as yet dynamically unsolved. One of Exner's most important contributions to the furtherance of the understanding of dune-mechanics is the full consideration he gives to the importance of the gravity of the sand, a factor which is almost universally overlooked by all other writers on dunes.

One consequence of the gravity of the sand and its r6le in an existing dune-

system may be mentioned in this place. The section shown by a dune is really the result of a counteraction between the influences of wind and gravity. On a

plain, leaning towards the wind, this must be stronger, if a sand-particle is to be moved, than if the plain is horizontal and no component of the gravity is directed against the wind. The wind blowing over a series of dunes has its

greatest power on the wind-sides, but here it has also to drive the sand upwards. In the valleys or on the level places between the dunes the wind has less power, but also less resistance to overcome when transporting the sand. Regarding the more

complicated conditions on the lee-side slopes some remarks have been made above.

From this it is clear that, at least under certain conditions, a dune.field offers

greater resistance to the transportation of the sand than would be the case if the sand were spread out evenly. When e. g. a dune-system is developed by a strong wind, another wind coming from the same direction but with less inten-

sity may be unable to move as well the sand on the wind-sides of the dunes because of the gravity, as the sand between the dunes because of the reduced

power of the wind when passing over the dune-valleys; the same wind may nevertheless be able to move the sand evenly spread out over a plain. The sand in a dune-system thus can be said to be arranged in a way offering resistance to transportation by the ruling winds, whilst, as already mentioned, it is easily moved by winds from the opposite direction.

On the lee-side of a moving dune the sand is so loose and slipping that a walker sinks down almost to the knee, whilst on the wind-side it is so hardly packed that the foot-prints go down only one or two centimeters. As far as I have found, the sand seems to be palpably looser on the crest of the dunes than on the lower parts of the wind-side. This difference in the packing of the sand is due to the previously exercised pressure of the overlying masses within the

dune, which compress the sand.


130 IVAR HO6GBOM

That the lee-sides of the ancient dunes are less steep than those of living ones

may partly be due to a subsiding of the looser sand under the influences of

changes in temperature etc. and partly to erosion.

Basal Forms of Dunes.

On the preceding pages the development of the dune-profile has been discussed; regarding this problem no great differences of opinion have appeared. Of more interest for this treatise, however, is the question of the development of the basal forms of the dunes. Regarding this, seemingly contradictory observa-

Fig. 3. Sketch showing schematically the deviation of the stream-lines of the wind when passing a curved dune-ridge.

tions have been made in nature, which have led to different opinions as to the mechanics of dune-wandering and, furthermore, to different interpretations of the

history of the ancient dunes of Central Europe. It is of great importance for the judgment of this question to establish the

changes in form which a primarily transversal dune undergoes when wandering further. Usually the opinion is advocated, that the wings of the dune move faster than the central part, because the former are lower and thus contain a lesser quantity of sand to be transported. As regards a single relatively short dune with the highest point in the centre, this may really be the case, and then the dune gets the shape of a barchan. In nature, however, things are mostly not so model-like, and the initial transversal dunes show irregularities such as an uneven accumulation of the sand-masses in different parts of the dune and a more or less sinuous basal form. On shores the latter deformation is due to the

irregular run of the shore-line, and as dunes often develop in open bays the bend often turns its concave side against the wind from the beginning. It is easy to show, that the sinuosities are accentuated when the dune is wandering forward that is to say, the straight transversal form of a dune cannot remain, but tends to become bow-formed, turning the opening against the wind.

The sinuosities of the dunes have a twofold influence upon the transporting


power of the wind. As the wind strikes the dune at different angles in the middle of the curve and on its flanks, it is deviated not only vertically, but also

horizontally; the curve-flanks of the dune serve, so to speak, as funnels for the wind, strengthening its power in the central parts of the curves and lessening it in the parts protruding against the wind (cfr Fig. 3). Furthermore, in the centre of the curves the wind passes the dune-ridge perpendicularly, so that the sand has there a shorter distance to pass from the wind-side to its resting-place on the lee-side. In extreme cases, when the horse-shoe form of the dune is fully deve-

loped, the sand is transported along the flanks, feeding the centre with new material, while the flanks get the character of longitudinal dune-ridges. These forms are often met with in the German fields, where the elongated dune-flanks often show only insignificant differences in the inclination of the slopes on both sides of the ridge.

From the interior of great deserts, where the initial conditions play a subordinate r6le, there are instances of systems of straight and very long transversal dunes. Such are e. g. described by Hedin from Asia. It seems as if in these cases, through lateral interference, a great wave-like movement of the air is de-

veloped, giving rise to a purer system of transversal dunes. As such are not characteristic of the fields here to be dealt with, it is not necessary to enter further upon their development. Amongst the dune-fields mentioned in the sequel only that of Nyirseg in Hungary in some places shows almost straight dune-ridges.

Where sand is deposited in patches which may be due to limited, local supply or to conditions offering a more local initial resting-place for sand which otherwise would have been blown further, the typical barchan develops. The formation of this kind of dunes has been fully described and analyzed by Cholnoky (1902), who, however, regards the barchans as the final forms into which also transversal dunes normally divide. According to the above, this development, if occurring at all on free dunes, is at least limited to the cases when the sand-mass is not

great enough to permit a continual wandering of the whole dune undivided. In

regions which are half-fixed by vegetation and where wind-furrows cut through the dune-ridges, the remaining parts may, on the other hand, get barchan- like forms as well as longitudinal forms, depending upon the character of the

vegetation and the type of the sand-field. Unlike Cholnoky, I should thus believe that transversal dunes are as good forms as barchans, and that the former are characteristic of regions where the sand-supply is great, the latter of

regions where the sand-supply is insufficient to build up continuous ridges, or, under special conditions, of regions where vegetation plays a r6le, in the way it does in some of the Hungarian fields.

132 IVAR H O GBOM

If thus, in my opinion, the amount of the detached sand in the first place determines the form of the dunes, it is obvious that the wind too plays a r6Ie. If strong wind is blowing, the sand may be transported so quickly that a relatively small quantity of sand falls within a unit of the dune-bearing area, and thus barchans develop where a weaker wind would have produced transversal dunes. It is also very possible that winds of different intensity produce differences in the

A

Fig. 4. A, basal form of a small barchan (Walther 1912, p. 262). B, basal form of a great barchar.

(Cholnoky 1902, p. io6).

shape of the barchans or the transversal dunes, but no

investigations in this respect have yet been carried out. In order to show the difference in the basal form

of barchans and bow-formed transversal dunes, I reproduce in Fig. 4 two barchans from actual deserts. Illustra- tions of different forms of transversal dunes; almost

straight ones, bow-formed, U- and V-formed ones, will be found in the sequel in the description of the different fields. The absolutely fundamental difference in

shape between the barchans and all sorts of dunes which have developed out of transversal ones needs no further comment than this reference to the illustrations. It is astonishing, however, that Tutkowski, Solger, and other authors have nevertheless without reservation

regarded the typical barchans and the bow-formed transversal dunes as being essentially the same forms, and thus concluded that also the winds driving the latter have come from the convex side. The incom-

patibility of the basal form indicating winds coming from one direction and the profile indicating winds coming from the opposite direction - which, in fact, must result from a confounding of transversal dunes and barchans - has led Solger to suppose that the German inland dunes have primarily been driven by east-winds, but that later west-winds have reversed wind-sides and lee-sides.

Influence of alternating Winds.

Among the many problems yet unsolved there is one which would be of particular importance for the comprehension of the climatic conditions giving rise to the ancient dune-formation, the question, namely, of the influence of variations in the direction of the wind on the shape of dunes. Several scientists have observed and described the changes of profile caused by a shifting of the wind to the opposite direction. Besides, Baschin (1903) gives an illustration of the changes in the basal form of a barchan under the same conditions. All these observations, however, refer to the ephemeral stage after a temporary shifting of the wind. How especially the basal form adjusts itself under the influence of winds


of alternating directions, on the other hand, is entirely undetermined. There is a

priori no reason to suppose that the shape of the dunes will be the same, if

exposed to a constant wind corresponding to a resultant of various winds, or, on the other hand, only to the wind-direction predominant among them. A closer

acquaintance with these questions would perhaps render possible a more correct reconstruction of the wind-conditions and, consequently, of the climatic conditions at the time of ancient dune-drift in Europe, than is now to be attained. As it is, one must generally be content with conclusions as to the predominant winds

during the sand-drift season, based upon the orientation of the dunes, which indicates

only the resultant of the different winds, but not the constancy of the wind; in certain cases, however, we are able to form plausible conclusions in this respect also.

There are two essentially different possibilities for the influence of shifting winds

upon the formation of the dunes. Either there are formed two dune-systems, possibly interfering with each other, corresponding to the different winds. This seems in fact to be the case, if the two wind-directions are sufficiently divergent. Thus Hedin describes (1904, I, p. 349) a very fine double dune-system from the Tschertschen desert. Regularly developed large transversal dune-banks run here in the direction NNW-SSE, with their steep lee-sides to the WNW. Lesser

ridges, by Hedin named >thresholdsv, separate the deepest hollows, the >bajirs>, which thus fall within the meshes produced by the two systems of dunes. Accord-

ing to Hedin these two systems correspond to the two main wind-directions which alternate at different seasons. However, the great transversal dune-ridges are not oriented quite perpendicularly to the prevailing ENE-winds but somewhat obliquely. This Hedin ascribes to different supply of sand in the northern and the southern parts of the field. Similar interfering systems caused by changing gusts of wind are also often on a minute scale shown by ripple-marks.

There is every reason to suppose, however, that such double systems of dunes come into existence only if the frequency maxima of two sufficiently separate wind-directions are rather marked. If, on the other hand, the angle between the wind-directions is not so great or the winds vary more evenly without two distinct

frequency maxima, such a double system cannot arise, but a simple dune-system ensues, oriented according to the resultant of the winds and showing forms more or less similar to those caused by a constant wind.

Certain general conclusions may, however, as mentioned, be formed regarding the frequency of the dune-driving wind. Very long dune-fields, extended in the wind-direction, may thus be taken as indicating that sideward winds, which would otherwise have broadened the field, have played a very subordinate part. Of course an investigation of the stratigraphic conditions, especially in the wings of the horse-shoe dunes, would also throw light upon the variations in the direction of the sand-driving winds.

134 I VAR H O GB O M

Secondary Dune-forms.

The difference in shape between dunes which have developed freely and dunes which have resulted from the counteracting powers of sand-driving wind and

sand-fixing vegetation merits special attention, as it is often of theoretical importance to find out whether secondary dune-drift has been active as a destructive force within the ancient fields.

Beyond the general speculations already mentioned about the supposed im-

portance of vegetation as a necessary condition for the formation of dunes, the aeolian action in half-fixed regions and the resulting topographical features had been almost entirely neglected, until Cholnoky (I9o02) took up the problem and advanced a systematic distinction between different dune-forms.

When for some cause or other the wind does not attack a sand-heap or a dune

uniformly, but only in certain spots, it operates in a peculiar way, cutting out a wind-furrow running in the direction of the wind. Often such a wind-furrow is terminated by a special sort of a dune, a garmada. These two forms, the wind-furrows and the garmadas, have first been described and subjected to detailed study by Cholnoky, who has also introduced the corresponding terms into the literature (I902, p. 123). The usual cause of the development of wind-furrows is that the vegetative covering is incomplete or that it has been locally destroyed in some way or other. The trampling of cattle, for instance, may have that effect.

The wind-furrows have sometimes a considerable length. In Nyirseg I have followed a wind-furrow for more than 6oo m. The section is cupular because the surface-layers offer harder resistance to the wind than the lower layers, which are not interwoven with root-fibres or chemically cemented.

The garmadas develop at the ends of the wind-furrows, if the wind has not the power to transport the material further. Thus garmadas usually are found on the lee-sides of the heaps cut through by the wind-furrows or in places where the ground inclines in the direction of the wind. When an edge is developed on the garmada, it runs in bow-form with the concave side against the wind. Sometimes several garmadas develop in one and the same wind-furrow; in this case part of the sand is obviously transported over the garmada, killing the ve-

getation leewards and thus enabling the deflation to continue.

According to Cholnoky, wind-furrows and garmadas may also develop in dune-

regions where vegetation is entirely wanting. As a particular instance he mentions that the groove between two barchans lying close to each other may deve-

lop into a wind-furrow and a garmada. This process might thus, although pro- ceeding on a narrower scale, be regarded as similar to that above (p. 130) described as causing the horse-shoe forms. Not having myself had the opportunity to


observe any barchans in such a position, I am not able to form any certain

opinion of my own about the probability of this development. I feel, however, rather inclined to regard wind-furrows as characteristic only of half-fixed regions. It is evident that the explanation I have given of the formation of the horse- shoe dunes cannot be applied if the primary bends are too narrow; in this case, on the contrary, a smoothing out of irregularities takes place. It seems to me more probable that this is the case if two barchans join each other laterally. Maps showing barchans grown together in present-day deserts also support this

opinion (e. g. Walther, I912, fig. 138, p. 262). For the development of the typical long wind-furrows two conditions are ob-

viously necessary. The wind must be regular, and the sand-heaps which are to be cut through must be of sufficient extension in the direction of the wind. If this is not the case, breaches will occur in quite the same manner, but without the forming of long furrows; and when the wind is variable in direction no garmadas, or only incomplete ones will develop. The most conspicuous features in a partly overgrown dune-region, which has been exposed to such irregular destructive influences of the wind, are the remaining witnesses of the old dunes, in German named )>Kupsten>). These are characterized by the cup-shaped excavations which the wind is always working out where the vegetation causes a particular resistance in the superficial sand-layer. Cup-shaped excavations often

appear also on the crests of the dunes, if the vegetation has been strong enough to check a complete breaking through.

The finest examples of this kind of dune-topography are to be found in some

coast-regions inside the outermost shore-dune, for instance on the North Sea coasts of Denmark, Germany, and Holland.

Contrary to the opinion which I have set forth (p. 130) regarding the development of bow-formed dunes from straighter transversal ones, some authors (e. g. Braun, 1911, Jessen, 1918, p. 235) regard the first-mentioned forms as the result of sand-drift in half-fixed regions. According to their views, the lower flanks of the dune-ridges will in the first place be more or less fixed by vegetation, on account of which the moving will there be slackened, and thus by the wandering- further of the central parts the dune-ridge will become bow-formed. Besides the very typical way, described above, in which the wind works in half-fixed

regions and there causes quite other alterations on the existing dune-ridges, this

hypothesis as a general explanation is also contradicted by the model-like symmetry and regularity of consecutive trains of bow-formed dunes met with in many places. The first fixation of dunes by vegetation and, consequently, the further

drifting of the sand in the unfixed parts must be rather capricious and cannot

give rise to such regular development on broad fronts, the causes of which,

136 IVAR HO0GBOM

therefore, must be sought for in some physical processes, as I have done above. When

describing the German fields, I shall have an opportunity to return to this question and to illustrate it by some typical maps.

In this connection some few words should also be dedicated to the dunes in-

vading vegetation-covered ground. Instances of that kind are met with almost

everywhere in the dune-bearing coast-regions. Evidently the existing vegetation has very small influence; only if the dune is invading a forest the trees may be a means of weakening the winds and checking the dune-drift, but in other cases the dune goes on wandering until the wind-side becomes overgrown.

Characteristics and Forms of the Dune-fields.

Dunes are often described as shore-dunes, river-dunes and inland or continental dunes. This classification indicates the regional occurrence of the dunes, but must not be taken in a morphological sense, as the different dune-forms are not bound to their different geographical positions. It is true that the influence of a coast or a river usually involves a primary development of transversal dune-ridges running parallel to the shore-line; but on the other hand well-developed systems of transversal dunes are found within great deserts, just as barchans sometimes occur within the regions of coast-dunes.

From a genetical point of view this terminology may be used as indicating the sources of the dune-driven sand, but extensive dune-fields are often termed inland dune-fields, although the dune-sand out of which they are built up primarily may have been furnished from the cuttings of rivers in sandy deposits. Besides, it is often impossible to ascertain how far the formation of a dune-field has been due to the action of a river. This is particularly the case with some of the ancient fields in Germany. I have thus preferred to use the term inland dunes as in-

cluding all dunes which are not genetically bound to present or former coast-

regions.

The shape of the dune-fields often indicates certain conditions under which the dune-drift has taken place. Sometimes the dune-fields are extended in the direction of the prevailing wind. This seems in fact to be the normal development of all fields, if the sand-drift continues for a sufficiently long time, and if the

wandering of the dunes is not checked by the decreasing power of the wind, by the vegetation or by topographical conditions. These factors determine the width of the coast-dune zones. When, however, the dune-drift goes on in a more arid region, the dunes continue their wandering so that the fields get their extension in the direction of the wind even if the sand-drift comes from a river bed. This

development of the dune-drift can be traced on some of the ancient fields in

Germany and Poland.


In such dune-fields, extended in the direction of the sand-driving wind, the orientation of the dune-ridges mostly seems to be to a certain degree dependent upon their place within the field. This is manifested by a tendency of the dunes near the sides of the dune-zone to arrange themselves obliquely and finally, at the very border of the field, longitudinally in relation to the wind. Thus, near the borders of the fields a general striking of the dune-ridges often develops, following a curve similar to that of a simple horse-shoe dune. I shall have an opportunity to illustrate this development when describing some of the ancient dune-fields.

The Dune-sand.

Generally the dune-sand consists of quartz-grains intermixed with some few percent of grains of other minerals. Usually the quartz-grains are rounded on account of the grinding process during the sand-drift. In dunes which have not wandered any considerable distance, however, the grinding has been too insignificant to allow a distinction of the aeolian sand from the sand of aquatic depositions. In this case the sand contains also a considerable amount of other minerals than quartz, if such are to be found in the primary deposits. Notwith- standing this, a microscopical analysis often shows the difference between samples of aeolian and aquatic sand, because of the characteristic dimensions of the former.

The upper limit for the size of the grains is determined by the limited transporting power of even strong winds (supposing that coarser sand is available in the primary deposit). The lower limit for the size, on the other hand, depends upon the finest material being transported further by the wind and deposited as loess, and not in dunes. Even the dust produced by grinding during the wandering of the dunes is blown away, as the grinding takes place under the influence of the wind.

According to examinations of samples of dune-sand from very different regions of the earth, grains of more than 2 mm section are only exceptionally met with in dune-sand, and even those of 1-2 mm play an insignificant r6le; sometimes they are quite lacking, and sometimes they amount to one or a couple percent of the sand-mass. The average size of the grains is in most samples between 0.2 and 0.5 mm. These figures are mentioned by Sokol6w, (I894, p. 132), and most determinations of other authors accord with them.

However, the sand of the ancient inland dunes, which are the subject for this treatise, is usually far less completely assorted than is the dune-sand of the great deserts or of the coast-regions, where, in the latter case, the waves outwash the finest material of the sand before it is made available for the direct action of the wind.

138 IVAR HO0GBOM

The following table gives the percentage of some characteristic sand-samples I have taken on different ancient dune-fields. For the mechanical analysis I have used the series of sieves constructed by Atterberg, riddled according to his classification of sand (Atterberg 1903).1

Size of the grains in mm: 2-0.6 0.6-0.2 <-0.2

Sweden: The Mora Field, Dalarna

.................... ............... 2.6 0 87.7 o 9.7 %

Tulusjirvi, Lapland .......................... . .. .

......... 3,4 - 84.4 12.2

Merasjarvi, Lapland ....................... ............. o.o 74.4 25.6

Tiirendo, Lapland .................................... ............ 3.3 82.o 14.8

Germany: M elchow, Prussia.......................................... 2.5 66.1 31.3 Rietschen, Prussia.................................. ................ 10.7 87.5 1.8 Seckenheim, Baden............................................. 6.4 89.0 4.6

Hungary: Mairia Pocs, Nyirseg, Kdm. Szabolcs ..................... o.o 90.0 1i0.0 Pilis, Nyirseg, Kom. Szabolcs

............................ o.o 88. x11.9

Pusztaszentimre, Kom. Pest .............. ............ 4.6 87.4 8.0

Because of the bedding within the dunes, the taking of samples must be done

very carefully, if good averages are to be got of the percentage of grains of different dimensions. In fact, small samples from the same dune may give widely differing results if they are not taken across a suite of beds. Mostly cuttings allowing such a procedure are not available; and so the samples are of less value from this point of view. In the above table I have thus preferred to give the results of some representative samples, instead of averages of a greater number of less reliable ones.

1 The sieves constructed by Atterberg, which I have used for the determination of the coarseness of the sand-grains, consist of four cylindrical steel-vessels which can be attached one above the other. The bottoms of the three upper ones are perforated with circular holes, the diameters of which are 2 mm, o.6 mm, and 0.2 mm respectively. A great disadvantage of this apparatus lies in the time it takes to sift the finest particles through the 0.2 mm sieve. For the moving of the sieve I therefore used an electrically moved cradle by which the sieve was pulled 6 cm horizontally to and fro 150 (?- 5) times per minute. In order to get an idea of the time necessary to move the sieve for determining the percentage of the finest grains, I carried out some series of sievings, noting the amount of sand which passed the o.2 mm sieve during each five or ten minutes from the starting. It proved most advantageous to use small samples, only weighing some ten grams, as the sieving was then practically completed in half an hour. If the sample contains very fine dust, this often shuts up the holes and makes a repeated cleansing necessary.

The 0.2 mm sieve used by me had only some 1.4oo holes, whilst the diameter of the sieve-bottom was 95 mm. Evidently it could be greatly improved by a denser perforation.


Sokol6w (1894, pp. 2, 288) has tried to find out the maximum size of the sand-

grains which can be moved by winds of different velocity. The results of his

investigations in that respect are given in the following table (the wind measured at four inches above the ground):

Force of wind, m/sec. Max. size of grains, mm.

4.5- 6.7 0.25 6.7- 8.4 0.5 9.8-11.4 I.o

S11.4-13.o 1.5

These empirically found values agree very well with the theory, according to which a diameter of the greatest objects (of the same shape and gravity), that can be moved by a fluid, increases proportionally to the square of the speed of the fluid. This accordance is in fact astonishing, if regard is

paid to the irregular shape of the sand-grains. Fig. 5 shows how well the figures of Sokol6w

agree with the theoretical curve.

Sokol6w has found the figures mentioned by observing sand consisting of grains of different size moved under the influence of winds of different intensity. The result would have been

slightly modified, showing lower figures for the maximum sizes, if the wind had been blowing over sheets of equal-sized sand, for in sands of

1.5 mm +.

05

0 z

• 8 10 1Z,/5ek.

Fig. 5. Diagram showing the relation between the speed of wind and the maximum size of sand-grains transported. The

points correspond to the values found by Sokol6w.

mixed dimensions the finest grains are blown away leaving the coarser ones fully exposed to the wind, but in the case of assorted sand of the maximum size, which otherwise would be moved by the wind, the grains shield each other and are thus less exposed to the wind. This must in still higher degree be the case if even coarser grains are present. In fact, the residual covering of coarser sand on deflation surfaces affords these conditions, which thus have to be taken into consideration as a means of checking further deflation.

It lies near at hand to base conclusions as to the intensity of the dune-driving winds on an examination of the size of the sand-grains in a dune. The conclusions arrived at, however, are of a very restricted purport because of the influence of other factors than the power of the wind. In the first place the dimensions available for wind-transportation must be considered. At the distal parts of a dune-field it has to be considered that on account of the grinding and the enrichment of finer material, no grains at all of the maximum size correspond-

140 IVAR HOGBOM

ing to the stronger winds are to be found. This may. naturally be the case even with proximal dunes, if the primary sand-deposit is exclusively made out of finer material. On the other hand, if the dune has the usual lee-side strati-

fication, the deflation surface of the wind-side, cutting this stratification discord-

antly, generally presents sand of all dimensions found within the dune, until, if only feebler winds are blowing, a lag film of coarser residual grains has covered the surface, thereby possibly checking further drifting. If a dune contains a

relatively great amount of coarse sand, this is no sign that strong winds have been blowing regularly, but only that the dune has been more resistant against feebler winds and has moved only when attacked by harder winds. From the above it is evident that the speed of the moving dunes depends not only upon the intensity of the wind, but also upon the size of the sand-grains.

CHAPTER II.

Ancient Dunes of Fennoscandia and Denmark.

The dunes within the more central parts of the once ice covered region of

Europe are insignificant in number and extension compared to those of the south-

ern, more peripheric parts. Thus there is in the whole of Fennoscandia only one more regular and collected dune-field, that near Mora in Dalarna (Dalecarlia); even this, however, is of small dimensions in comparison with the greater ones in Germany and Poland. But in some ways the Swedish dunes present greater advantages for a scientific treatment than the southern ones because of the possibilities of determining their age by studying their relation to the postglacial changes of the sea-level. Thus it seems proper to begin with the Scandinavian dunes and to allow comparatively ample space to the description of them, even in a study which aims at a treatment of the whole problem of the ancient inland dunes of Northern and Central Europe.

There are two different kinds of ancient dune-bearing regions in Sweden which

present the essential subject of this chapter. The greatest and best developed dunes are all of them situated on the glaci-fluvial marginal deltas, immediately below the highest shore-lines of the finiglacial sea. The other ones, which usually lie scattered and are of smaller dimensions, are to be found at some places amongst the different glacial accumulations above this niveau. A third group of ancient dunes in Sweden will also be mentioned in the sequel, namely some in the province of Vdsterg6tland which prove to have been formed during a later

epoch than those connected with the glaci-fluvial deltas.

Finally, there are at places in Southern Sweden dunes, which were formed as

shore-dunes, corresponding to the levels of the sea at different epochs. The


EXPLANATION

A *B Ice-Border at Beginning of finiglacial Tingie7

1a•'V Last Ice-Sheds Highest Finil/acial Shore Dune-Occurrences on marginal Deltas Dune -Occurrences on higher Levels

SCALE 1:8 000 000

89

0

atoo 16) d

Fig. 6. Map showing the situation of the Fennoscandian dune-occurrences in relation to highest fini-

glacial coast-lines and last land-ice remnants. - i. Romerike; 2. Geijersdal; 3. HIllefors; 4-6. Siljan-

region; 7. FRrila; 8. Kubbean; 9. Studsviken; io. Aspsele; ti.

Kusfors; 12. T!irend6; 13. SaitajAirvi; 14. Merasjirvi; 15. Vittangi; I6.

Vastakielinen; i7. Tulusjirvi; A8. Kemijoki; 1g. Raudunjoki; 20. Lutto-

joki. (I-V mainly after Holmsen, A. G. H6gbom, G. Fr6din, and Gavelin).

142 IVAR HOGBOM

favourable conditions for dune-drifting, always offered by the shore-lines, however, make these dunes less interesting, as they bear no direct evidence of the climate at the time of their formation. Accordingly, I desist from entering upon the questions connected to these dunes.

From Norway only one ancient dune-field is reported, situated on the marginal delta-deposits in Romerike.

In Finland, which for the most part lies below the level corresponding to the main dune-bearing regions of Scandinavia, the existence of true inland dunes is noted only at a couple of places in the northernmost parts of the country.

The situation of the main dune-occurrences in Fennoscandia in relation to the

highest finiglacial sea-level and the divides of the last ice-remnants is marked on the map Fig. 6.

With some few comparatively unimportant exceptions, which will be mentioned later on, recent dune-drift in Fennoscandia takes place only at some parts of the shores.

Dunes in Middle Sweden.'

The Mora-Field, the greatest of the ancient dune-fields of Scandinavia, is for the first time mentioned in the geological literature in an abstract of a paper read by Sten de Geer in i908. In a guide written for the excursionists of the Inter- national Geological Congress held at Stockholm i9io he gives his opinion about the age of the dunes: >Vielleicht schon vor der Einwanderung des Waldes hat der Feinsand durch den Wind Diinentopographie angenommen.> The first topographical maps of the General Staff of these regions drawn on a scale of i : 5o,ooo, appearing a couple of years later, offered a good opportunity of estimating the regional distribution of the dunes. The part of these maps including the Mora Field was reproduced 1913 in A. G. H6gbom's >Fennoscandia> (1913, p. I15), and in the same year I wrote a short study on this and the neighbouring dune- fields (1913). I tried there to show the late finiglacial' age of the dunes and

In accordance with the usual Swedish way of speaking, )Middle Sweden> is here to be taken as a synonym for Svealand, which in fact is a part of the southern half of the country.

2Here, as in the rest of this treatise, I use the term >finiglacial,

in accordance to the nomenclature of G. De Geer (1910, p. 1146). The finiglacial age thus comprises that part of the late glacial epoch, when the ice-border receded from the great belt of terminal moraines in southern Sweden (the Salpaus- selki stage in Finland), and till the breaking through of the ice-remnant in eastern Jiimtland (marked III on the map Fig. 6). This incident is chosen by De Geer to mark the end of glacial time. The gothiglacial epoch, preceding the finiglacial one, designates according to the same nomenclature the time during which the ice-border receded from the southernmost part of Sweden to the great moraine belt named.

At the beginning of the last chapter of this treatise a synoptical table is inserted, which shows the length of these epochs as well as some other data of the late glacial and postglacial history.

Against the terminology of De Geer some justified objections have been raised, especially by Munthe


suggested falling winds coming from remnants of the land-ice sheet, at that epoch yet remaining, as the climatological reason of the sand-drift.

The situation of the Mora field, as well as that of the other dune occurrences in the Siljan region, is shown by the sketch-map Fig. 7, in which also the run of the highest finiglacial shore-line is drawn.

The marginal terrace of Osterdalilven, the greatest part of which falls within the map Fig. 8, extends its distal front from Vamhus atthe north- western corner of Orsa- sjon along the west-side of the same lake and the northernmost part of Sil- jan down to a point about 8 km south of Mora. The area of the whole delta is about ioo km', out of which some 20 km2 are

dune-bearing. According to determi-

nations by Hedstr6m (1893, p. 159), the highest finiglacial sea-level lies in this region at about 215 m altitude.' The uppermost parts of the Mora- delta reach an altitude some io m below this highest sea limit, whilst by far the greater part of it is situated at a level of

P- 7 0u n

3 , am. Nlii ....

-1 iiiii

Fig. 7. Sketch-map showing the situation of the dune-occurrences in the Siljan region: i. Mora-field; 2. Oreilv; 3. Skattungsj6n; 4. Gagnef; 5. Gustafs. Dark shaded areas present lakes. Light shaded areas

Finiglacial Sea.

(191i), Lid6n (1913, p. 30), and Enquist (1918, p. 102). I have, however, chosen to follow the terminology first proposed as a final agreement about a new one is not yet attained.

4 Hedstr6m found the highest marine limit at Lattniiset east of Orsasjbn at 219 m, supposing the level of Siljan to be at 165 m. According to later nivellements, the altitude of Siljan is stated to be 16I m on the maps of the General Staff, and consequently the highest finiglacial sea-level may be 215 m above the present sea-level.

144 IVAR HO0GBOM

200 m and slightly below. The lowest parts of the marginal terrace slope down to about i8o meters altitude. The gentle descent, which extends outside the terrace along the shore of the Orsasjon with a breadth of a half to one kilometers, has been abraded during the further sinking of the sea-level and thus represents a younger land-form. The same is the case with the extensive lower postglacial delta-deposits situated outside the mouth of the meanders of the Osterdalalven, the greatest part of which represents a redeposition of the material cut out from the marginal terraces (cfr Fig. 8.)

The finiglacial age of the main delta can be concluded not only from its situation immediately below the highest sea limit but also from its character of a

pitted-plain with typical kettle-holes (Germ. >)Solle# or >Pfuhle>) of different sizes, the biggest ones forming the small lakes visible on the map.

As these small lakes are without superficial outlet, the changes in their level must be a consequence of changes in the ground-water level. It is also evident that the latter is very sensitive to the changing precipitation and evaporation during different years. Thus the changes in the level of the little lake Lintjarn comes out very markedly in its north-eastern corner, from where during more humid years a branch is temporarily sent out over forest-covered ground. When I visited the field in 1913 there, for instance, were to be seen not only the trunks of drowned young firs but also a new forest generation 8-io years old, showing that during one or more seasons some io years previously the level of the lake was about one meter higher than at the time of this observation. On the west-side of the Osterdalilven I have had an opportunity to ascertain corresponding and yet greater variations in the ground-water level (cfr Fig. io d). That the

amplitude of the variation is much greater here is due to the swifter running away of the water because of the proximity to the river-side, as well as to the

temporary existence of superficial affluents to the pools in question. The existence of water-springs at the foot-line east of the dune-bearing plateau

shows that the present ground-water level almost reaches there. The higher sea- level during the last phases of dune-drift has thus only slightly influenced the level of the ground-water at that time, compared with the present ground-water level.

The recent changes in the ground-water level, however, are worthy of notice as they have been caused by the comparatively small climatic variations during different years in our time. Thus they indicate that the level of the ground- water has been subject to relatively important variations due to the different climatic conditions succeeding each other during postglacial time. If the altitude of the ground-water plays any r6le at all for the vegetation, its variations must have accentuated the direct influence of the climatic changes during different

epochs.


Loso 168

it161,f2 -

"r M

CC Ve3Nmz

LA

77t

GEN. STAB. LIT ANST.

Fig. 8. Topographical map of the Mora field. Scale I 75,00ooo. (From the sheet Mora of the maps of the General Staff).


146 IVAR HOGBOM

The finiglacial delta, as well as the dunes lying on it, is covered with pine- forest. For further information regarding the vegetation I refer to the paper of G. Samuelsson (191io).

The situation of the dunes on the delta plateau is clearly shown on that part of the map of the General Staff reproduced on Fig. 8. Broadly speaking, the dunes occupy a zone which extends with a breadth of up to three kilometers

along the distal margin of the part of the delta bordering the Orsasjdn. On the south-western side of the Osterdaldlven the dunes recur at the railway station Eldris. Besides, there is a dune-bearing spot some three kilometers west of the

village Morastrand. The distal parts Of the delta, on the other hand, are quite free from dunes on this side of the river. This is probably so because the conditions regulating the running off of the water have been so unfavourable that the ground has been kept humid enough to prevent sand-drift even while dune-formation has been going on in other parts of the delta. The extensive

bogs now existing seem to confirm this explanation.

Single dunes occur also here and there within the more proximal parts of the delta, e. g. west of Gr6ningen, as well as amongst the oses above the delta proper, east of the Gopshusberg and elsewhere.

Already the topographical map shows the regular development of the dunes, these having their length-direction orientated in NE-SW. They are mostly of well

developed bow- or garland-form, turning the open concave sides towards the north-west. Everywhere a marked difference between wind- and lee-sides is found, the former usually sloping 8-1 i, the latter 20-250, and rarely somewhat steeper.

The dunes are thus typical transversal dunes driven by nortk-westerly winds.

Although the edges naturally have been somewhat rounded, and it is thus impossible to point out their exact position, the profile of the dunes seems not to be of the type with the edge lying leewards from the crest, but of the more triangular type, where edge and crest coincide.

Several dunes can be followed for a length of one kilometer or more. The western dunes are more scattered with level ground between, whilst the eastern ones are thronged together, the lee-side of one dune lying immediately unto or on the wind-side of the following one and the ridges forming a ramifying net of garlands. In fact, near the margin of the dune-bearing delta the aeolian accumulation has surely laid down far more material than what is visible as dune-ridges on the map. The western parts of the plateau, on the other hand, have been subject to deflation, as not only the development of the detached dunes wandering over a distinct plain makes probable, but also a study of the coarseness of the sand gives evidences of. Whilst the sand-grains within the dune-bodies as well as in the eastern dune-valleys only rarely reach the dimensions of m mm, a


residual enrichment has taken place on the plain in the west, where dimensions of up to 3 mm are very common on the surface.

The usual height of the dune-ridges is about 8 meters in the central parts,

# I/

--

,

V

..

I It

/',/

12 I

12

f6!

Fig. 9. The south-eastern corner of the great dune-field north of Mora. 4 m. aequidistance between the full line isohypses. The o-isohyps following the foot-line of the dune-bearing plateau corresponds to the finiglacial sea-level at the end of dune-drift time and lies at about

i8o m above present sea-level.

but there are some, e. g. in the south-eastern part of the field, which reach

I2-1I4 m.

The map. Fig. 9 gives a more detailed illustration of the dune-morphology in the south-western corner of the great dune-field. The more north-south length-

148 IVAR HOGBOM

direction, generally shown by the dunes in the immediate neighbourhood of the mar-

gin of the delta-plateau, is most probably due to the general tendency of dunes with a marginal situation to arrange themselves parallel to the border of the field (p. 137). In this peculiar case the sloping of the plateau may also have played a r6le in

retarding the movement of the northern dune-wings. As the profile Fig. Ioa shows, the plain descends considerably, wherefore the north-eastern wings of the dunes have been less exposed to the driving winds than the south-western ones, which thus may have advanced with greater speed. It is also possible that the proximity to the shore has contributed to the deviation of the length-direction of the dunes because of the delaying influence of the humidity of the ground on the lower situated north-eastern dune-wings or because of counteraction of irregular winds

blowing from the sea.

A fairly exact determination of the time when the dune-drift ceased, is possible, owing to the development of the brink of the dune-bearing plateau. At the northern and middle parts the field is relatively high. There the conditions do not allow an exact determination of the end of the dune-drift time, as the sea

may have gone on sinking and abrading even after the sand-drift had ended, until the foot-line of the plateau was reached, although under such circumstances the

sharp development of the latter is not easily explained. This line lies in the north at 185 m and in the south at 179 m, a difference in altitude which may partly be caused by the gradient of the postglacial land-rising, which has been greater in the northern than in the southern part of the area. That no dune- drift has taken place since the sinking of the water to this line is evident, as no dunes exsist beneath it, although fine sand is everywhere at hand. That, on the other hand, dune-drift has continued until this line was attained, is proved by the development of the profile in the southernmost part of the field. There the surface of the plateau slopes down till it almost reaches the foot-line, the brink being there only a couple of meters high. Here too, the plateau bears dunes; in fact some of the highest ones lie on the border of this south-eastern corner of the field, as is shown by the map Fig. 9 and the profile fig. Io a.

The dune-drift on the Mforafield has thus continued until the sea had sunk about

35 m below its highest level

Investigations regarding the rate of the ice-recession in these regions have not been carried out, so an exact determination of the situation of the ice-border at the end of the dune-drift time is yet impossible. In the valleys there run

big oses, but usually no conspicuous summer-accumulations can be traced indicating the annual regression of the ice. At one place (2 km north from Ladein, on the Alfdal railway), however, I found some consecutive ose-hills, lying about 50 m from each other, which certainly represent annual depositions. These interspaces


are probably exceptionally short, but the general convergence of. the aequirecesses' to the west proves that the melting away of the land-ice must have been relatively slow in these parts of the country compared with Middle Norrland, where Lid6n

(1913) found 360--400 m per year in the coastal region, and Carlzon (g1913) 100- 150 m near the ice-shed. In Varmland Aronson (191 1) found the distances between the annual ose-hills averaging about 70-85 m. A rough estimation of

a ESE

b SE

N W SE

Fig. Io. a. Schematic section from Lintj irn to Orsasj6n. Dunes dotted. Dotted lines indicate

present ground-water level and the level of the Finiglacial Sea at the end of the dune-drift epoch. - b. typical cross-section of a dune. - c. the brink of the plateau at two different places. -

d. changes in level in a small pool at Eldris. (I. H6gbom, 1913).

the annual recessiorf of 0oo m a year in the Mora region seems in fact to be in

fairly good accordance with the statements of Lid6n, Carlzon, and Aronson, when regard is taken to the general convergence of the aequirecesses westwards. In Angermanland the upheaval of the land after the retreat of the ice has been determined by Lid6n to I I1-14 m per century. With due regard taken to the somewhat lower sea limit in Dalarne, the sinking of the shore-line can there be supposed to have been about 10o m per century. As the dune-drift ceased when the sea- level was about 35 m below its maximum, it may be concluded that the sand-

driving foehn-wind reached only some few tens of kilometers from the ice-border.

1 The term ,aequirecess, is introduced by G. De Geer as signifying the position of the ice-border at a certain time during the recession of the land-ice. (Geol. F6ren. F6rhand. Bd 27, p. 220, Stock- holm 1905).

150 IVAR HOGBOM

The dunes have thus developed in a periglacial situation in the strictest sense of the term, and accordingly it lies nearest at hand to explain them as having been caused by foehn-like winds coming from the land-ice. The form of the dunes

however, prove that the driving winds have been blowing from the north-west whilst more northerly winds or even north-east winds would have been prevalent if an anticyclone, above the cold centre presented by the ice, had been the

only factor determining the distribution of the air-pressure. This deviation of the wind accords in fact very well with the opinion about the general distribution of the air-pressure and the wind-conditions based upon a study of the Middle

European dune-fields, which will be presented in the sequel. I shall also have an opportunity to return to this matter in the final chapter, when reviewing the

climatological conclusions which can be drawn from the study of the dunes. At some of the small kettle-hole lakes there are dunes which run parallel

to the shore and close to it, independently of the usual length-direction of the dunes. Probably these dunes have been driven during a later time when the other dunes had already been fixed by vegetation, and the favourable conditions offered by shore-lines were necessary, if sand-drift was to take place. Even these dunes however, are under present climatic conditions quite fixed. Similar instances of later sand-drift at the shores of small lakes are to be found also on a pitted-plain near Gustafs mentioned below.

With the exception of the northernmost part of the field, where the forest has been wasted by a fire, and some smaller spots at the eastern margin of the field, where the vegetation has certainly been destroyed by the action of man, the present vegetation is entirely fixing the dune-sand. To the north, on the other hand, the heath-vegetation leaves many spots bare, especially on the dune-ridges, from which sand blows during hard winds. In fact, at a visit in 1913, I had the

opportunity to witness a real sand-storm on a minute scale; and according to statements in a newspaper the road beneath the sand-plateau were covered by sand in one place last summer. One should have believed that, during drier climatic epochs than the present, forest-fires have been far more destructive than now. In another connection, however, I have (1916) had the opportunity of poin- ting out the peculiarity of the Mora-field which has kept all primary characters in

spite, not only of the climatic changes passed, but even in spite of the fires which must have passed over it.

It is in fact astonishing that no secondary action whatever can be found on the dunes within the Mora-field. Neither >Kupsten> nor more regular wind-furrow- or garmada-forms disturb the transversal dune-system. The dunes must then have been very quickly fixed by vegetation, or a relative calm must have reigned during the time of the immigration of the vegetation, or - most probably - botth these factors have been cooperating. There can hardly be found any other cause for


such a rapid change in the climatic conditions than the recession of the border of the remaining land-ice. The non-appearance of secondary dune-forms would thus seem to confirm the hypothesis of the falling winds from the ice-rest as causing the dune-drift. It is true that the dunes in Germany and Poland also which, as will be seen further on, have not been driven by similar falling winds, are

surprisingly well conserved, but secondary forms are nevertheless not quite lacking amongst them.

The stratification within the Mora-dunes is usually very indistinct, because of the even-grained material out of which they are built. The cuttings where I have been able to observe any stratification at all are very few, and they do not permit a certain determination of the distribution of wind- and lee-side accumulation. The rules regulating where accumulation or deflation take place within different

parts of a transversal dune are not fully established and it is not to be expected that they can be revealed through observations of the conditions within the dead dunes. Amongst the Mora-dunes, I have, however, noticed both wind- and lee-side stratification. The only deeper cutting where the layers could be observed was in the flank of a dune showing wind-side accumulation, which observation is in accordance with the general remarks I have made when discussing the development of the basal form. The stratification is clearly visible only when the sand has a certain humidity, and mostly it is possible to get cuttings which are steep enough only for one or two decimeters below the surface, where the fibres of the roots as well as the chemical cementation and the humidity usually make the sand somewhat coherent.

The material which the sand-driving wind has blown together into dunes is

certainly for the most part derived from the marginal delta itself, but a minor

part may also come from the oses and moraines to the north-west of the plain. The existence of wind-worn pebbles and single dunes amongst the oses higher up, on the western side of the river, proves also that a sand-drift from the oses, important enough to give rise to dunes of relatively great dimensions, has really taken place.

The development of the level underlying surface on which the western dunes of the field have wandered can be interpreted as the result of one or other of two different processes. Either the humidity at a certain horizon has been sufficient to check the sand-drift, or the enrichment of coarser grains, which is always taking place on deflation surfaces, brought about the same effect. Most probably the latter has been the actual case on the Mora-field. The covering vegetation renders it impossible, however, to establish the coarseness of the grains of the very surface film, the state of which is decisive in this respect. Irrespective of the hindrance to observations set up by the vegetation, the plants have naturally themselves occasioned a disarrangement amongst the uppermost sand-grains and shattered

152 IVAR HOGBOM

the possibly once existing film of coarser grains. On other fields, where the wind still blows over spots of bare sand, I have had the opportunity to observe how the deflation continues until a film of coarser sand is enriched, which then shelters the underlying finer material from being attacked by the wind (cfr the

description of the Tirend6-field further on). That also on the Mora-field an enrichment has really taken place on the plain over which the dunes have wandered is, however, evident. Grains of dimensions of 3 mm are common in the

uppermost centimeters of the sand, but are only seldom met with at a depth of i dm. Because of the inhomogeneity of the material of the different delta-layers it is, however, hardly possible to get any quantitative idea of how far this enrichment has gone.

The dune-sand itself is more even-grained than the delta-sand, the former

showing neither dimensions above i mm nor in any considerable amount finer

particles than say 0.05. Where a stratification is visible, the broader layers contain sand, the medium dimensions of which are about 0.25 mm, whilst the thinner

layers contain sand-grains of up to 0.75-1 mm. The finer sand consists mainly of somewhat rounded quartz-grains, the coarser sand mostly of more or less

angular felspar-grains. As I have already stated in the previous chapter, the systematic study of

dunes has not as yet been carried so far that from an investigation of their forms it is possible to draw conclusions on the intensity of the driving wind (p. 132), and thus only limited conclusions in this respect can be based upon a study of the coarseness of the sand-grains. As mentioned the sand in the Mora-field consists of grains reaching a maximum coarseness of about i mm; coarser sand is anyhow so uncommon that it is not to be reckoned with in this connection.

According to the determinations of Sokol6w (cited on p. I39), a velocity of the wind of i I meter pro second, measured 4 inches (12 cm) above the ground, is

necessary to move grains of this size. As there are grains of greater dimensions on the plain between the dunes, which thus seem to have resisted the transporting power of the wind, one may judge that the velocity mentioned corresponds to the strongest winds which normally have been blowing over the dunes at the time of their wandering. Because in the measurements of Sokol6w the anemo- meter was placed immediately above the ground, the winds mentioned should in reality correspond to hard storms, when measured at the usual altitude above the ground. Unfortunately, exact investigations of the decrease in velocity of the wind near the surface have not yet been carried out. The data given by Sokol6w indicate, however, that the velocity of the wind under similar conditions is about twice as great at an altitude of a couple of meters as at an altitude of I2 cm, where his measurements of the transporting capacity of the wind have been made. For the movement of the thicker layers within the Mora-dunes which contain


sand of an inferior coarseness a velocity of the wind of about 5-6 m/sec, measured at an altitude of i 2 cm above the surface, would have been sufficient, but even this corresponds to a rather strong wind at the altitude of a couple of meters.

Wind-worn pebbles are to be found in the ose-region beneath the Gopshus mountain. Fully developed >Dreikanter> I have not met with, but the surface of some stones of the hard >Bredvad>-porphyry are often beautifully sculptured by the sand-driving wind. Because the felspar phenocrysts are less hard, compared with the quartziferous ground-mass, the former have in the first place been

ground by the wind, which thereby has got points of attack for a rifling even of the ground-mass. On stones which have kept their position the rifling is also orientated after the sand-driving north-west winds.

The sketch-map Fig. 7 shows the situation also of the other dune-fields or, properly speaking, the other dunes in the Siljan region. In fact, there is no other

dune-bearing area which in regard to regularity and development of the dunes can be compared with the Mora-field. The occurrences at the other places are better characterized as small groups of dunes or as scattered dunes than as dune- fields, which term should be reserved for greater and more regular complexes.

NE of the Orsasjdn, between the Oredzlv and its affluent the Unnin, there are some marginal delta-deposits lying at an altitude of about 215 m above sea-level, that is to say, just below the highest sea limit, which here may be supposed to reach some few meters higher than on the Mora-field. The dunes are few and do not show the regularity which characterizes those of the Mora-field. The last- mentioned fact seems rather to be ascribed to the humidity of the soil during the time of the dune-drift than to later destruction of the forms, for the dunes are here situated within a pronounced marsh-region, the drainage of which must have been yet more incomplete during the time of the dune-drift than at

present, when the streams have cut down their beds in the sediments. East of the

Unn.n there is also a dune, the north-south direction of which indicates

that it has wandered away from the river-side and originated as a river-dune. I have found no secondary forms as ~> Kupsten> or wind-furrows. Such forms are, besides, hardly to be expected here, as they are not met with on the far drier Mora-field. The wind- and lee-sides are on the whole orientated in the same way as on the Mora-field. Although the development of the dunes is less pronounced and does not allow an exact determination, the direction of the driving wind thus seems to have been about the same at both places.

154 IVAR HOGBOOM

Some scattered dunes occur NW of the Oresjon near the shore and at an altitude of some few meters above the surface of the lake. As this is situated at 200 m above present sea-level, no marked marginal terrace as that west of the

Orsasjbn here rises above the lake. The greatest dune is quite similar in shape to those on the Mora-field.

Judging from the topographical map, some dunes are also to be met with in the ose- and delta-region above Riittvik at the eastern corner of Siljan.

Further down in the Dalilv-valley dunes occur near the junction of Oster- and Vaster-Dalilven at Gagnef They are situated within an irregular ose- and delta- land, at an altitude of about 18o m above sea-level. Attaining only small di-

mensions, these dunes do not offer any features of special interest.

Yet further down in the same valley relatively well developed dunes are met with at Gustafs. They are, however, few in number, only three of them being of dimensions comparable to those of the Mora-field. They have a more north- south length-direction and show distinct wind-sides to the west and lee-sides to the east. Thus, they would seem to indicate that more westerly winds have been

ruling in this region during the time of the dune-drift than at Mora. However, the dunes at Gustafs are few, and, besides, the topographic conditions are such that they may have caused some local deviations in the winds and an irregular development of the dunes.

These dunes have formerly been interpreted as oses (Nelson, 1910, p. I70). A

comparison between their morphology and the morphology of indubitable dunes, e. g. those at Mora, however, leaves no doubt as to their true character.

The highest of the dunes reaches with its crest above the highest sea-level, which in these regions lies at about 195 m above present sea-level.

The dunes between Siter and Gustafs are the most distal ones along the Dal- alven or at least the most distal ones of such dimensions that their existence is revealed by the topographical map of the General Staff.

In this region also later sand-drift has taken place at different places. Com-

pared with the finiglacial dunes, the later ones are, however, very insignificant in size. They seem to be caused by different local conditions and are of a more occasional character. At some places they have been driven because a forest fire has destroyed the vegetation, as is the case at Solvarbo, where a dune has wandered out over burned ground. Near the small lakes south of this place the

changes in the level of the water have also been a means of providing sand for dune-drift. In all these cases the dunes do not reach over 2 m in height, and

usually they are yet smaller. Some of them have already been fixed by young


vegetation, which does not disguise their accidental character. It is, besides, very probable that such dunes would not be recognized at all, if they lay on uneven

ground covered with a grown-up forest. No conclusions as to particularly favourable conditions for sand-drift during present times are thus to be drawn from the existence of new dunes of this kind.

Dunes of the same kind as those described above from Dalarna are also met with at some other places in Middle Sweden and situated in the same relation to the highest finiglacial sea-limit on the glaci-fluvial marginal deltas.

The only ones which have hitherto been mentioned as dunes in the literature are those described by Sundius (1922, p. 50) from Hiillefors and other places within the Grythytte region in the westernmost part of Vistmanland.

Sundius describes the greatest dunes as beeing of an ose-like shape, not showing any difference in the steepness of wind- and lee-side. This statement is remarkable, beacause no large dunes elsewhere in Scandinavia exhibit so symmetrical a development of the dune-profile, although some of the Lapland dunes are characterized by abnormally steep wind-sides (cfr below). Regarding the Hillefors dune it seems probable that the wind-side has got its steepness because of se-

condary erosion, if the high-water level of the lake St. Sangen can be supposed to have reached the foot of the dune. This cannot be decided by a study of the map, and I have not myself visited the place. The statement of Sundius that the normal lee-side stratification (250) changes in the highest parts of the dunes to a more gentle one, seems also to indicate a secondary overblowing of

sand, perhaps in connection with erosion at the basis of the wind-side. In spite of the symmetry of the dune-profile there is no doubt about the ridges being real dunes, which is clear as well because of the basal forms as because of the coarseness of the material. The basal form of the Hillefors dune is of typical horse-shoe shape with the concave side turned towards the north-west. With the

exception of one or two of the smaller dunes, where grains with dimensions up to 2 mm have been found, the coarseness of the sand varies from 0.25-1 mm whilst finer material has been blown away. The normal material of the Halle- fors dunes is thus of the same dimensions as that of the Mora dunes.

The dunes are undoubtedly originated by north-west winds, which is shown both

by the stratification in the interior parts of the dunes and by the basal form

opening towards the NW. Sundius, on the other hand - just as Solger does

regarding the German dunes - interprets the convexity as indicating south-east winds.

Next to the Mora-field in importance among the Middle Swedish dune-fields is that situated on the marginal delta of GeiTersdal in the province of Virmland.

156 IVAR HOGBOM

The main dune-complex in this region is described by Dahl (1902, p. 72)who, however, did not recognize the dune-character of the formation. His description runs as follows:

>)A couple of kilometers north of Svarta the hills, which rise above the sand-

plateau, begin to assume a more determined shape and direction, further accentuated on account of the bogs occupying the interspaces (cfr the topographical map). The hills appear, in fact, as long narrow oses with steep sides and attain

heights of up to about ten meters; the length-direction runs perpendicularly to the valley and the ends bend towards the upper parts of the valley. Thus they have approximately the form of end-moraines, but as far as I could see, they consist exclusively of a loose, finer or coarser sand. At the northernmost corner of Lake Alstern the waves had eroded the end of such an ose, causing a cutting some seven meters high. Even here no coarser material was exposed. - These

peculiar oses appear within an area of 3 km in length and 2'/2 km in breadth. I do not venture upon any explanation of their formation.>

Evidently there is no doubt of the dune-character of these formations. Their bow-form open to the NW and well visible on the topographical map is strikingly similar to the forms of the Mora-dunes. Even here sand-driving north-westerly winds may thus be established.

Judging from the topographical map, dunes occur also on the eastern side of Lake Alstern south of Lake Lungen. Further to the south they are, however, lacking on the map. A notice of Svenonius (1917, p. 4o): >Besides it is said that also sand-dunes of considerable heights appear on the heath> seems nevertheless to indicate that dunes are to be found even there.

The highest finiglacial sea-level lies in these regions at I80-Igo m, whilst the lowest dunes at Alstern visible on the map are situated at an altitude of about 167 m. This indicates that the sand-drift took place only during a very short period after the retreat of the ice and the emergence of the land. It is, however, to be noticed that even the higher parts of the delta are free from dunes. A closer study of the material of the delta will perhaps reveal the conditions which have made dune-drift possible at some places but not at others, although the topographical map in both cases indicates similarly constituted delta-

plains. I have not myself visited these dunes, as I know that they, as well as other

quaternary deposits in these regions, have been made the subject of a yet not

published, comprehensive investigation by my friend Mr N. H6rner.

Dunes in Southern Norway. From Norway dunes of the same type as the old Swedish ones are known on

the great finiglacial delta-deposits in Romerike. The delta is here a typical


pitted plain with no less than 25 small lakes and ponds of the same character as those on the Mora-field mentioned above. The glaci-fluvial deposits in Rome- rike are described by Bjorlykke (1912), who also calls attention to the dunes.

According to his description there are to be found )several bow-formed sand- walls of about io m height 100-200 m breadth at the base>. He notes further that the dunes turn their concave side towards the north. The dunes lie at an altitude of 200 m above sea-level and the highest finiglacial sea-level is in this

region at about 225 m. Because of the informations of Bjorlykke cited above, in my paper on the dunes.

in Dalarna, I judged that the Norwegian dunes were of the same late finiglacial age. This opinion has been confirmed by Bjorlykke in a later study (1918), which he devotes to the question if loess exists in Norway. Bjorlykke regards a fine dusty earth (>Romeriksmjele>), which is found in positions indicating aeolian and aquatic deposition, as being most probably the finest-grained equivalent to the dunes and spread out by the same winds, over the fjords and adjacent land.

It is interesting to note that the dunes in Romerike are driven by more north-

erly winds than those of Central Sweden. This difference in wind-direction is in good accordance with the theory of foehn-winds, as the ice-shed, and yet more, the ice-front in this part of Norway runs almost from west to east instead of south-west to north-east in Central Sweden. That the winds have blown almost

perpendicularly from the ice-front instead of sho wing the deviation to the right, which would be expected if the isobares had run parallel to the ice-front, is due to the general distribution of the air-pressure at the period in question, as will be treated in a later chapter.

For an exact determination of the direction of the driving wind further observations are, however, needed; the topographical maps of the Norwegian General Staff are not detailed enough to show the orientation of the dunes.

Dunes in Northern Sweden.

The existence of aeolian sand-accumulations on the delta-plains at the borders of the early postglacial and finiglacial Baltic Sea (the highest Baltic limit) is first mentioned by Lindstrom from the place Studsviken in Angermanland as

early as I888. He makes, however, no suggestions as to the -time or the conditions of their formation. A. G. H6gbom (1906, p. I69), having met with similar dunes at other places at the same Baltic limit, regards them as being of fini-

glacial age and as having been driven as shore-dunes when the deposits in question emerged from the sea.

Later on K. Sandler (1917) in his study on the glaci-fluvial marginal deltas in

Angermanland has devoted some pages to the dunes in that region, showing

158 IVAR HO0GBOM

that they are of the same character as those of Dalarna, which had at that time been described by myself.

During magnetometrical work in the region east of Kiruna in Lapland in the summer 1916, at some places I met with old dunes on moraine- or ose-ground, most of which are now covered with pine-forests or else fixed by vegetation. As ancient dunes had not at all been reported among the quaternary deposits in

Lapland, I thought them worth some attention, and having got some further information as to their occurrence also at other places from Dr B. Hogbom, I made a journey through this part of Lapland last summer in order to investigate the

morphology of the dunes and to get an idea of their frequency and regional distribution. In Lapland an inquiry of this kind is hampered by the lack of topographical maps on a sufficient scale to show the dunes, as the General Staff map over Northern Sweden is on a scale of I:2oo.ooo.

No detailed geological survey is as yet made of these vast and sparsely populated regions, and the geologists who have worked there have had their attention fixed on other problems of greater importance for the knowledge of Lapland and have thus left no notes regarding dunes. Under such circumstances it has been im-

possible for me to try to find out more than a few localities and I shall have to confine myself to a description of some of these. Thus the map Fig. 6 does not pretend to show the regional distribution of the dunes in Lapland in general, but only the situation of the few localities which I have found out during some

journeys, comparatively short, however, considering the vast extent of the regions in question.

In the following description of the dune-occurrences in Norrland, I begin with those situated on the flniglacial deltas and thus in all respects most closely connected to the dune-occurrences described on the previous pages.

In HlIsingland a marginal delta extends for some I15 km along the Ljusne River, north-west of Farila, and there some few dunes occur. The highest fini-

glacial sea level in these regions lies at about 240 m above present sea-level.

(Hedstr6m, I893, and others), while the surface of the main part of the delta lies at an altitude of about 200-2Io0 m. Judging from the topographical map, some few dunes are to be found within the proximal half of the delta, whilst none are marked within the central and distal parts. This indicates that the wind has not been dry or strong enough to produce dunes after the emergence of the lower

parts of the delta from the sea, that is since the land had risen some 40 m after the regression of the ice-border. From the map one can hardly draw any precise conclusions as to the direction of the dune-driving winds.


From Northern Angermanland Sandler (1917, p. 98) describes dunes at three different localities on the marginal deltas, namely the deltas at Aspsele and Studs- viken on the Gidealv, and that on the Kubbedn. Besides, he thinks it probable that a sand-ridge running W-E on the delta of the Lockstain, flowing to the Gide-

ilv, is really a dune.

Among these localities the Aspsele field contains the largest and finest developed dunes; they have a height of" 5-12 m, are bow-shaped and turn their lee-sides towards the S, SE or E and have consequently been blown by north-westerly winds. According to Sandler's statement, the grain-size would seem to be a little finer than usual. One of the dunes thus consists of loam with grains of dimensions under 0.2 mm, while it is stated about another that the material consists of sandy loam with sporadic grains of I mm size.

The dunes at Studsviken lie in a region with complicated ose-topography. The dunes having in some cases wandered out over hollows, their lee-sides have got an abnormal height, 15- 20 m in places, and as these lee-sides are to some extent free from vegetation, the dunes have become unusually prominent and have, therefore, already early been noticed and recognized as aeolic formations. Their shape indicates that they have been driven by north-westerly winds.

That the lee-sides of these dunes are at least in part bare of vegetation is rather curious. I have not myself visited the field, but I think it very likely that the vegetation has been destroyed by man or perhaps rather by the trampling of cattle.

About the sand-formations at the Kubbedn Sandler states: > Even on the topographical map an isolated, finely developed dune is clearly visible in the south. eastern part .of the delta. It rises 9 m above the neighbourhood and has wandered towards the SE so far that its bare lee-side borders on the adjacent moraine

ground.>) Sandler sums up his observations thus: > The dunes here described in Northern

Angermanland are of the same character and age as those previously more mi-

nutely described dune-occurrences in Dalarna (I. Hogbom, 1913). Like these, they are situated in the immediate neighbourhood of the marine limit and have been formed by north-westerly winds from the constant barometric maximum lying over the inland-ice not yet melted away. - As the lowest dune at Studsviken lies 2 12 m above the sea and the Baltic level at Aspsele is 256 m above the

sea, the sand-driving winds have continued blowing at least till the elevation of the land had moved the shore-line to a level 40o-50 m further down.

>With the rate of the land-elevation measured by Lid6n of o10-14 m per one hundred years, this means a period of 3-400oo years. But during that time the ice-border had receded i oo-15o km into the country, if the annual recession had been 360-4oo m, as Lid6n found it to be in the inner parts of the Anger-

160 IVAR HOGBOM

manland fjords. - The, dune-forming winds were thus able to assert themselves even since the ice-border had reached the region not far from the ice-shed.>

Dune-formations of the same character as those in Angermanland are certainly to be found on other finiglacial deltas in Middle Norrland, but these have

Fig. I. Dune cut by the railway. Petikan.

not as yet been examined in sufficient detail. In some places the dunes may, however, be seen even from the railway. This is for instance the case near the station of Kusfors on the Skelleftediilven. Dunes occur here on both sides of the

river, but perhaps most fully developed on the northern river-bank about 6 km above Kusfors at an altitude of about 15 m above the river-bed and some 210o m above sea-level.

The dunes in this place are both numerous and of considerable dimensions. A couple of open horse-shoe dunes which I haVe traced out, turn their opening westwards. As, however, their northern wings have wandered up a slope, the basal-form of the dunes may possibly have been influenced hereby, and so it is not to be positively concluded that right westerly winds have reigned. Very likely a closer examination will show that these dunes too have been driven by north-westerly winds.


On the Petikin, which joins the Skellefte~alven immediately south of Kusfors, the railway cuts through a beautiful dune (phot. Fig. i i). It lies at an altitude of about 185 m. Sand-drift thus seems to have continued at the finiglacial delta of the Skellefteailven at least till the sea had sunk to near 60 m below the highest Baltic level, that would say during some six centuries (cfr p. 159).

There are dunes between the Skellef-

teilven and the Vindelalven also; they have, however, not been subject to

investigations.

Some of the finest horseshoe-dunes I have met with in Sweden, are to be found not far north of the village of

Tdrendi, by the high-road to Juno- suando. No exact determination of the

highest Baltic Sea level has been made for these parts, but it is with tole- rable certainty to be placed at about

I75 m above the present sea-level. The sediments about the junction of the Tarend6 and Kalix rivers have the character of glaci-fluvial delta-formations. The dunes, included in the

map Fig. 12, lie at an altitude of I65 -170 m, immediately east of the Ta- rendo river on the proximal part of the delta. The altitude indicated of the highest sea limit stands in good accordance with the estimates arrived at by an extrapolation of the figures known from places somewhat SE of this region (cfr Sj6gren I905).

I have not had the opportunity of

reconnoitring the other parts of the

j' 0

OOrm.

5/

, (

-----------.

• "-;,

- 4

',

5

. • , Z.

Fig. 12. Horse-shoe dunes on the Tirend6 delta. 5 m

aequidistance between the full line isohypses.

delta-formations in this region in order to find out whether there are dunes on them. That this is the case, however, seems highly probable. In Tanner's treatise (1914, p. 433) the following passage is quoted: >)At Pahtamaa Svenonius (diary of 1891) found well developed, sharp ose-ridges, 10-12 m in height and composed by pure sand.> These were no doubt dunes. The name of Pahtamaa is not to be found on the map of the General Staaff, but there is a name Pahtakorva 3 km

I I Geogralfska Annaler 1923.

162 IVAR HOGBOM

south of the church of Tirendd; the report may be supposed to refer to this

neighbourhood. The north-easternmost one of the two large dune-segments visible on the map,

has, measured along the ridge, 1.8 km in length. The northernmost part, measur-

ing 300 m, takes, however, an abnormal course compared with the rest of the dune-

segment, probably because it has got the character of a later shore-dune which has not yet wandered far enough to lose its parallelism to the shore.

Outside the dune-bows there are mostly peat-bogs. Within the north-eastern dune-bow forest-covered sand-heaths prevail; within the south-western one, peat-bogs.

The plain on which the dunes are situated rises only some few meters above the level of the river. The dune-sand has been supplied not only by the erosion of the river, but a great part of it must have been blown off the surface of the plain itself; this is clear from the easily appreciable enrichment by coarser sand and gravel to be noticed in the gaps of the dunes, where the surface of the ground is not covered with bog or has been blown over with sand. On the sand-surface, where it is bare of vegetation, as is the case in spots here and there, coarser sand- and gravel-grains, up to a size of i cm are found on the

superficial layer, while they are of rare occurrence one or two decimeters down. The sand of the dunes has the dimensions typical of dune-sand, and consists

chiefly of rounded quartzgrains. One sample from the very surface of a bare spot and another taken 2 dm

below it show the following dimensions of the grains: Size of grains in mm: > 2 2-0.6 0.6-0.2 <•0.2

Surface.................... 19.2 % 4.0 % 75.8 % I.o % 2 dm below

............ 1.9 I I1.6 84.4 2.1 Dune-sand ..............0.0 3.3 82.0 14.8

The dunes reach a height of 7-10o m measured at the lee-side. Generally the difference between wind- and lee-side is clearly developed, 15' may be put as an average for the former, 250 for the latter. The unusually steep lee-side in the central part of the southern dune-segment, however, is remarkable; the difference of inclination between wind- and lee-side is there insignificant.

Ramifications from the two great dune-segments occur in several places, and there is a number of smaller dunes as well in the mapped region as in the western

neighbourhood. Judging from the basal forms of the dunes, the sand seems to have been

driven by winds between NW and N.

It is true that no systematic search for dunes has been performed in Norrland and that new occurrences are certain to be observed, since attention has once


been directed to the dunes as a special and evidently not very rare formation. It is improbable, however, that future observations will bring anything essentially new regarding the regional distribution of the dunes, and thus regarding the lower limit of their occurrence. In several places, especially in the coast-land of Vister- botten, there are large sand-heaths, which would have furnished abundant material for dune-formation, if the conditions as to wind and humidity had allowed such

during any period after their emergence out of the sea. It is very improbable that such formations should have escaped observation altogether, especially as

they, as is the case on the finiglacial deltas, would be topographically much more

prominent than dune-fields occurring above the highest sea-limit. Besides, the

regions below the highest sea-limit have been rather more closely examined in regard to the quaternary geology than those above it, and the system of roads is much more developed, which should also have facilitated the discovering of dunes.

Even if the lower limit of dune-formation in some places should be moved down-

wards, therefore, this cannot be expected to take place to any considerable extent, and there is no likelihood that evidences will be found for an essentially different

apprehension of the extent of the dune-forming epoch. The correspondence between the occurrences of dunes on the marginal deltas

in Norrland and in the better known Middle Sweden are also striking, and the observations from Middle Sweden must be considered as supporting the inter-

pretation based on the occurrences of the less investigated Norrland.

The dunes situated above the highest finiglacial sea-level in Lapland, which I am going to describe on the following pages, are in some respects of another character than those which have developed on the marginal deltas. As no determination of their age can be made by studying their position in regard to a former sea-level, no direct conclusions in that respect can be drawn. On the other hand, there is evidently every probability, that even these dunes have de-

veloped in a periglacial situation. That they often emerge out of peat-grown marsh-ground indicates that other hydrographical or climatic conditions than

nowadays must have been ruling at the time of their formation. The present sand-drift in these regions is, besides, far too insignificant to account for the formation of these dunes.

The north-westerly winds, which the orientation of these dunes generally in-

dicates, pass in these regions the border of the ice-rest more obliquely than was the case farther to the south, as the ice-remnant at the time in question terminated to the north in these regions.

It should be reminded of the somewhat later age of these dunes compared with

164 IVAR HIOGBOM

those earlier described which were formed already before the regions here in

question had been freed from the land-ice. The conclusions as to the winds from the different dune-regions cannot thus be unreservedly connected in order to reconstruct the climatic conditions of a certain stage of the melting away of the land-ice.

As the existence of dunes above the highest sea-level has hitherto, as mentioned, been quite overlooked, I have thought it appropriate to illustrate the appearance of these occurrences in somewhat greater detail than their relatively insignificant dimensions, compared to other dune-fields, would otherwise have required.

The highest situated dunes I have visited are at Tulusjirvi near the Lainio river, north of Ovre Soppero at about 400 m altitude. Following the highroad down from this place for some 150 km to Tarendb at the highest Baltic sea level, which reaches here about 175 m altitude, I have met with dunes at several places. It is true, that this road passes some broad valleys, where the conditions seem

particularly favourable for the development of dunes, but as the following description will show, dunes at these altitudes are as often fed by sand from oses or moraines as from delta-deposits. As the oses in these regions run almost independently of the valleys and mostly across them, the possibilities for deflation of the oses and deposition of dunes beneath them seem to be at hand almost

everywhere. As the cuttings of the roads through the dunes best show their true character, it is quite natural that dunes have not yet been reported from the interior of this region as long as they have escaped attention along the roads. Besides, a detailed investigation and mapping is mostly necessary to distinguish dunes from other formations, as the forest does not permit a direct recognition of their basal form.

An instance of the typical combination of oses and dunes, which seems to be very common in Lapland, is found at the southern end of Lake Tulusjairvi, north of Ovre Soppero (cfr Fig. 13). There are also dunes farther north in the ose-country along the high-road, as well as farther south on the gravelly ground of the table-land west of the Lainio river. These dunes I have not had the opportunity of examining, but it does not seem probable that they would show any new traits beyond those shown by the dunes at Tulusjarvi or in other districts.

Across the Lainio river there runs a considerable ose-range, the main part of which, according to Tanner's map (1914, Plate I) lies to the west of Tulusjirvi. The northernmost part - visible on my map, Fig. 13 - of the great ose Tulusharju, which rises 20 m above the neighbourhood, is thus a side-branch of that great ose-range. Tulusharju runs in SW-NE and has some very fine dunes on its


south-eastern side. On the south, beyond the region mapped, the ose borders to the SE on marsh-land and is not, with one small exception, further accompanied by dunes.

The dunes reach a height of 5-6 m measured on the lee-side, and even more farthest to the NE, where, however, the topographic conditions are not quite normal, and where erosion may possibly have played a part. Nei- ther their basal form, as shown on the map, nor their cross-section, leaves any doubt that they are driven by north-westerly winds. The schematic profile Fig. 13 indicates further, how the ose itself has been

overspread with sand on its lee- side. In many places the dune-

ridges, as well as their sides, exhibit gaps with recent, cup-shaped winderosion excavations, which is the typical beginning of

,Kup- sten>-formation and consequent destruction of the primary dune-forms.

There is no other source of the sand-material of the dunes than the

ose, and the absence of dunes further southwards helps to prove the influence of Tulusjdrvi by de-

taching the sand. Though the ose holds much fine-grained material, it is evident that the deflation would have ceased long before such great quantities of sand had been driven away and heaped up in dunes, if the shore had not at the same time eroded the steep wind-side slope of the ose.

A B

o

--.•o o o

o

o ooo

o

0

-- oo o

?

o

o,6-o

o

oo

o 0oooo

0 1o

o0 o o

07 0 0

o

,0 0

c 0 0 0 00m

0 0,

02

Fig. 13. Dunes at TulusjRrvi, Lapland. i. ose- and moraine

ground; 2. bare spots of dune-sand. In the section all dune- sand dotted. 5 m equidistance between the full line iso-

hypses.

Mechanical analyses of samples of the sandy gravel from the ose and sand from the dunes gave the following percentage:

Size of grains in mm: >2 2-0.6 0.6-0.2 <0.2

Sandy gravel from the ose...... 19.4 % 19.7 % 60.2 % 0.6 %

D une-sand................................ 0.0o.o 3.4 84.4 12.2

166 IVAR HO0GBOM

The comparatively great mixture of finer and coarser material in the dune-sand is usual in samples from the Lapland dunes and is evidently due to the local

development of the dunes, which have wandered only an insignificant distance and thus not been subject to the separation process which assorts the sand in real

wandering dunes. The low amonut of the finest material in the sample from the ose is probably due to outwash by water on the steep ose-side from where it is taken.

Another and larger instance of the Lapland dune-topography is to be found at Vastakielinen about 8 km north of Vittangi, not far from the high-road. The

sketch-map (Fig. 14) of this field, here presented, has no pretensions to detailed

accuracy but may give a faithful idea of the topographic features of the country. Because of the complicated nature of the dune-system an exact mapping would take up much time and probably give no new results; I have, therefore, confined

myself to a fairly accurate rendering of the limits of the dune-district, as it rises out of the marsh-land, while the run of the main dune-ridges has been only schematically delineated.

In this district, likewise, there is a marked ose running NE-SW. This ose, however, cannot be supposed to make up more than part of the upland situated to the NW of the dunes, the greater part of which is probably composed of moraines. As the moraine often shows a tendency to fluviatile stratification and indications of kames-morphology, it is difficult to make out the distinct boundary between moraine and ose, where no very deep cuttings are available. This moraine- and ose-region extends to the NW of the dunes, so that the northern

part of these constitutes a direct continuation of the former. In this field a large area has probably provided the material of the dunes, and the erosion of a brook

along the northern side of the moraine hills and of a little lake to the NW may have helped to detach the sand.

The brook indicated on the map, which now flows round the eastern part of the dune-complex with a very small volume of water, has earlier cut a minute erosive terrace, as can be seen for a considerable stretch of the lee-side of the distal dunes.

These dunes are far less typically developed than at Tulusjarvi. This may be noticed above all in the unusually steep wind-sides, which are common to almost

every one of them and for which it is difficult to give a reason. Secondary erosion

may have played a part, and a tendency to such may be traced in this field even where bare spots are now wholly missing. This, however, does not entirely account for the extraordinary steepness of almost all the wind-sides. Unmistake- able dunes with exceptionally steep wind-sides, however, are known from other

places; as already mentioned, the Hitllefors dune, according to the description by


Sundius, shows quite a symmetrical profile. As regards the formations in

question, their character of dunes can

hardly be doubted, though they show some deviations from the regular dune-

type both in basal form and in profile. The material is typical dune-sand,

nor have I found any stony material within the area mapped as dunes and dune-sand. Within the northernmost

part of the area, denoted on the map as moraine, I have, on the sandy surface, found some small stones of the size of one or two cm, which cannot

very well have been carried thither

by non-geological means. They may be lying on the crest of a moraine hill, which to some part is covered with aeolian sand.

,ooooo o oooo oo f

.a :. ooo o o o o oi oooo ooo ? ./ \ oo o o ooo?:''

> 0 0 0 0 0 00 0 0ooo0 o o o o 0:o 0 o o o oo 000 o o o

C,: 0 o0 o0 o0

..:.'.::

0 0 0 0 0 ooooooo

0oo ooo o

1of o o ::;:

Fig. 14. Dunes at Vastakielinen north of Vittangi, Lapland. r. moraine and ose-ground; 2. dune-sand;

3. main dune-ridges; 4. marsh-ground.

About Vittangisuvanto, as well in the village of Viltangi itself, as across the river, there are dunes of a different character (Fig. 15). Here it is the deposits through which the river flows that have provided the sand, and in certain respects

--0

V. o5 o

Fig. I5. Dunes at Vittangi.

the dunes have the character of shore-dunes, at least those in the village. These dunes have previously been noticed by Svenonius

(cfr Tanner 1914, p. 430). The furthest part of the point projecting

into the river, north of the village, is com-

posed of a moraine or an ose-hill, but the

ground between it and the two dunes is very low, only one or two m above the level of the river. It is not improbable that the dunes were formed while the level of the water was higher, and have then drifted a little landwards to their present position. The weather need not have been so very much drier than at present, when these dunes came into existence. A recent dune of about the same dimensions is to

168 IVAR HOGBOM

be found on the map furthest to the NW. The southernmost part of the dune here marked out is, in fact, at present drifting and quite unfettered by vegetation. In the dunes at the village of Vittangi there is also some sand-drifting on a small scale going on, but it is wholly destructive. In the cuttings caused hereby, both wind- and lee-side stratification is to be observed. The curved dune-complex in the north-eastern corner of the map may probably be considered to have

originated from the ose-plateau to the NW. The spur to the SE has in part the character of a shore-beach.

About 20 km south of Vittangi, on the high-road immediately south of the

village of Merasjlrvi, there is an ose, with dunes on its eastern side (Fig. 16), thus a complex quite similar to that mentioned from Tulusjarvi. The basal

ri

5

0

0

O RO!

Fig. 16. Dunes at Merasjiirvi, Lapland. To the west an ose, 1,7 m equidistance between the iso-

hypses. Dunes dotted. White areas outside the ose mostly marsh-ground. G. gravel-pit. S. stone

found on one of the dunes.

form of the dunes seems however to suggest a little more westerly winds than was the case at Tulusjdirvi. To a certain extent, this is also confirmed by the stratification, as it comes to light in the road-

cutting in the northernmost part of the map, showing a distinct lee-side stratification

falling about 250 against the NE. The wind causing it must accordingly have been more westerly than the dune-branch run-

ning NW- SE. The dune-sand appears to have come partly from the ose and

partly from the sandy moraine-ground and the glacifluvial plains to the NW.

I have thought proper to indicate in the

map the occurrence of a great stone (about 3-4 dm), which, however, I suppose to have been brought thither by man, probably by Laps, though it is isolated and is not of the sort which the Laps commonly use for their fire-places. In fact, the dunes have

certainly been particularly convenient for the camping of the Laps, and I imagine that here as elsewhere the finds of single stones hereby is sufficiently accounted for.

I cannot think that there is any doubt that the formations at Merasjarvi have

really the character of dunes, as their basal


form as well as the stratification in the cutting mentioned above are quite consi- stent with such an interpretation. As is the case in other places where the dunes rise out of marsh-land, the difference between wind- and lee-side is not well marked; besides, in this instance >Kupsten>-formation has played a part in the mo-

delling of the dunes. The sand-material also shows the dimensions characteristic of dune-sand.

By the road running from Junosuando down to Saitajarvi, about 3 km from the last-mentioned place, there is another dune-area. The dunes here exhibit a more typically developed profile, because the dune-valleys are not covered with peat-bogs. The dunes turn their concave wind-sides to the NW and W, and the sand-material is the usual.

Wind-worn pebbles I have not found in Lapland. This is mainly to be ascribed to the coarse granitic material of the oses, which does not readily lend itself to the grinding processes and which besides, partly on account of later weathering and partly because of present lichen-covering, cannot be expected to show the

polish of sand-grinding or >dreikanter> details.

In several parts of Tanner's survey of the ose-formations in northern Fenno- scandia (1914) one comes across expressions which seem to suggest the occurrence of dunes, though they have not been interpreted as such by the observer. This is particularly the case with many quotations and excerpts which Tanner has collected from earlier notes and diaries. Where he cites expressions as >great quantities of sand and ose-like hills> or >great quantities of meagre sand forming here a level field, here hills and osesp, it is with pretty great probability to be

supposed that among these formations there are dunes also. That the idea of sand-dunes has not occurred to the several observers, is not surprising, because hitherto dunes as obvious as those at Tirend6 described above have not been noticed as such by the geologists, who have surely passed the high-road, that cuts through them. Hence I hold that dunes of the type mentioned are by no means uncommon above the highest sea-level in Lapland, though, occurring within or in the immediate neighbourhood of hilly ose-regions, they have not been topographically so prominent and have therefore been overlooked as a special formation. It would be very curious indeed, if so marked dune-

drifting had been going on only in single places here and there, when, according to the reports of all earlier geologists about sandy ose-districts etc., all conditions

regarding supply of material are of general occurrence to the same or to a still wider extent than in the dune-bearing localities I have had the opportunity of

examining.

170 IVAR HOGBOM

The position of the dunes described above shows that they have been formed somewhat later than the dunes situated on the marginal deltas. There seems, however, to be no essential difference in the conditions for their formation. The direction of the sand-driving winds agree here better with hypothetical isobars

enclosing the land-ice, but this might partly be ascribed to the valleys running in the expected direction of the winds.

Dunes in Finland (and Karelia).

In his survey of the quaternary formations of Northern Finland, Tanner (1914, Plates XII, a, b, and XI) shows three maps including dune-formations. As the text gives very few data regarding these, however, it is very difficult to get a clear idea of their character. Two of the maps are from the parish of Sodan-

kyla, the third one from that of Enare. One of these dune-accumulations, that at Raudunjoki in Sodankyli (Tanner's

Plate XII, a), is obviously of the same character as the Swedish ones. It is situated at the southern and eastern verge of a wide sandy plain, surely a mar-

ginal delta, at an altitude of 180-185 m above the sea-level. The dunes are

4-10 m in height and form one or two segments, rather irregular, however, and

open against the NW. On the E and S the dunes border on morainic ground. The shape of the dune-complex and its situation on the south-eastern border of the sand-deposit, leave no doubt that they have been driven by north-westerly winds; Tanner, however, does not state the location of wind- and leesides, but

says only that the original forms of the dunes are well preserved. The dunes are now entirely covered by lichens and pine-forest.

The other map from the parish of Sodankyla (Tanner's Plate XII, b) shows some dune-strings not far from the village of Martti on the Kem/oki. They lie at an altitude of 200-208 m above the sea-level, that is to say about the highest Baltic Sea limit. Tanner thinks it probable that the dune-bearing ground represents a local deposition of sand in an ice-dammed bay. Tanner denotes on his map by several arrows what he supposes to have been the probable direction of the

accumulating winds, namely S-SW. No information is given about the topographic features of the dunes, which have led to this conclusion, but as the arrows generally cross the edges of the dunes obliquely and show great divergences one from another, it is obvious that Tanner does not found his suppositions on the general location of the wind- and lee-sides of the dunes, but rather upon details of form. These may, however, be only secondary and due to late displacements, supposing that the testimony of the dunes as to the direction of wind is not simply mis- interpreted. The shape of the principal dune-segments as well as their situation in relation to Kemijoki, and the existence of smaller dune-hills on the north-


western side seem, contrary to the opinion of Tanner, to indicate that the dunes were driven by north-westerly winds.

The dunes on the Luuto river in the parish of Enare (Tanner's Plate XI) are of a different type. They are situated on the northern side of the river, which here runs mainly in a W-E direction, and have wandered upwards from it as shore-dunes; they may also correspond to an earlier river-shore, and this is made

probable by their situation on one and the same isohyps. Just as is the case in regard to the Swedish Lapmark, one gets from Tanner's

collection of data concerning Finland the impression that in several places dunes have probably been met with by geologists without having been recognized as such. Regarding one or two of these localities, Tanner himself makes the suggestion that we may have to deal with aeolic accumulations. From the informations gathered by Tanner out of the diaries of other geologists it is, however, impossible to draw any definite inferences as to the presence of real dune-formations. The manifested presence of dunes in some places makes it nearly certain, however, that there may occur dunes in several other places, as all the geological conditions necessary are very common and the meteorological factors cannot have been locally so different that dune-formation has taken place only in one or two cases.

From the Kemijoki in Karelia Rosberg (1892, p. 85) has noted the existence of some small fields where nowadays dune-drift is going on, although on a small scale. He ascribes, however, this actual sand-drift to the burning of the forests here usual in order to gain arable land for cultivation, whilst the primary accumulation of the sand would have been called forth by winds from the inland-ice at the time when this deposited the Salpausselkii moraines, outside the northern extension of which the fields are situated. Ancient dune-forms are not mentioned

by Rosberg. On the other hand, amongst other recent forms the same author

gives also the description of a shallow wind-furrow, some two hundred meters wide.

Dunes in Southern Sweden.

Of quite another orientation and age than the North and Middle Swedish dunes described above, are some met with in the Province of Visterg6tland in the

surroundings of the table-mountains Billingen and M6sseberg, known from the

descriptions of Munthe to the geological sheet-maps Skara, Sk6fde, and Tidaholm. These scattered dunes seem to be most numerous NW of the town of Skara.

They have been built up from the ice-sea sand, that is the shore-sediments which were formed during the recession of the sea by the action of waves upon the moraine and delta deposits and, above all, by the outwash of finer material from

172 IVAR HOGBOM

the sand-containing Yoldia clay. The dunes attain, heights of 6-7 m, seldom more.

These ancient dunes have been the subject of an interesting study by Lund-

quist (1920), who has tried to find out their age by an pollen-analysis of the peat in the small bogs situated within the dune-fields, in order to ascertain in which horizon aeolic sand appears.

Lundquist gives also important informations regarding the orientation of the dunes, and shows that they have been blown by southerly winds. He states that the dunes NW of Skara with a general length-direction in WNW-ESE

(N 70 W-S 7o0 E) show wind-side slopes of Ioo-15' towards the SSW, and leeside slopes of about 200 towards the NNE. The dunes examined by him have a height of about four meters.

Quite similar are the dunes of the other field investigated by Lundquist, that at Svensbro, some 12 km south of the town of Skofde, only that they indicate winds coming from between S and SSE, the length-direction of the dunes being about WSW-NNE. (S 70-750 W-N 70-750 E). The run of the dune-ridges, however, is at places rather irregular (bow-formed?). The southerly wind-sides vary in steepness between xIx and 170, but even such of 200 have been observed. The

northerly lee-sides show inclinations of 25'-300.

Through pollen-analytical investigations Lundquist has found that the aeolic sand intermixed in the peat disappears in the layers corresponding to the beginning of sub-boreal time, and thus concludes that at the end of atlantic time or the beginning of sub-boreal time southerly winds were ruling in these regions. The most frequent winds nowadays during the summer-months are from W and SW.

It is somewhat unexpected that these dunes, although younger than those of the marginal deltas, where exceptional climatic conditions called forth the sand- drift, prove to have been in an active state at the end of atlantic time and fixed at the very postglacial change from cold-wet to warm-dry climate.

Further south dunes are also met with at some places. According to Munthe those at Hvalstad, being some 3-4 m high, indicate SW-winds. Thus they would seem to be of more recent origin, which Munthe confirms by mentioning that they have been fixed by plantation. Munthe also notes the occurrence of wind-worn pebbles from this place as well as from Dimbo, where a marginal ose

running E-W has been overblown by sand (cfr description appended to the geological sheet Tidaholm).

Dunes in Denmark.

Dunes are far more widespread on the west-coast of Denmark than in the regions hitherto mentioned; especially they are the distinguishing feature in the

morphology of the northernmost land-tongue of Jutland. They are essentially a


formation bound to the present coast-line, thus forming the northernmost end of the chain of coast-dunes, which, with some breaks, border the coast-line of the continent along the North Sea. A description of these dunes thus falls outside the scope of this treatise.

There are, however, also some aeolic deposits in the interior of the country which are not connected even with older coast-lines, but which have a similar geological situation to the Swedish ancient dunes, being built up from late glacial sand-de-

posits. Thus A. Jessen (1918, p. 234) says: >)It is probable that the sand- drift in Vendsyssel is as old as the land itself; especially at the end of the Ice

Age, before the new-formed land had been covered by vegetation and mould, there seem to have been conditions favourable to the formation of dunes.>> The

primary traces of the ancient dunes, however, are obliterated, at least no inland- dunes have been described, which have been fixed by vegetation without the in- tervention of man. The aeolic sands of the interior are either still active or fixed

by plantation. It is very possible that the study of the later sand-drift in Denmark will reveal

interesting data regarding changes in climatic conditions which have taken place during the last three or four thousand years. By the examination of the Danish

peat-mosses it has been proved, that the recent sand-drift along the shores has set in with all its intensity only some few centuries ago, and it is known from historical documents, that the sand-drift meant no great menaces to the cultivation before the beginning of the I6th century (cfr Jessen 1918, p. 239). As the last-mentioned change in the intensity of the sand-drift must have been called forth by changes in wind or humidity, it seems to contradict the experience hitherto won regarding the stability of the climate in historical time.'

For the sake of comparison with the figures given at other places in this treatise, the following averages from a series of 30 samples of dune-sand from Denmark, published by Warming (1907, p. 9), may be of interest:

Size of grains in mm: 2-I 1-0.5 o0.5-0o.25 <0o.25

Northern Jutland (8 samples) .......... 1.2% 1.9% 52.9% 44.o% W est-coast of Jutland (i i).................. 0.4 1.3 58.5 39.8 Coasts of the Kattegatt (3) .............. o.8 o.8 93.3 5.2

Coasts of the Baltic (4) ..................... 0 o.o 0.2 94.1 5.7 Interior of Jutland (4) ........................ 0 o.9 4-5 90.5 4. 1

Some remarks on recent dune-drift in Fennoscandia.

In order to form a conception of the climatic changes indicated by the existence of ancient dunes, it may be of some importance to know under what con-

1 There are no evidences of any changes of the shore-line at the time in question which could have caused a change in the exposition of the sand to the waves.

174 IVAR HO GBOM

ditions and in which regions sand-drift is at present taking place within Fenno- scandia, besides the instances already mentioned in connection with the ancient dunes.

With few exceptions all recent sand-drift is bound to the shores, where sufficient

quantities of sand are supplied by the action of the waves. It is already stated in the chapter on dune-formation that under such circumstances even great hu-

midity does not seem to prevent the formation of dunes. The sand successively made free at the shore-line always wanders a certain distance inwards before the

vegetation is able definitely to fix it. The inland winds do not drive any dunes because they have no starting line which supplies sand, and besides the inland winds only exceptionally reach an intensity great enough to balance the action of the sea-winds.

The ancient inland-dunes of Fennoscandia, on the other hand, have mostly been driven independently of shore-lines, even if they lie near them; in most cases they have wandered towards the shore under the influence of land-winds. It is especially to be remembered that the geographical distribution of the dunes on the

marginal deltas is due only to the widespread sandy accumulations and to the climatic conditions during the time in question, but not to any influence of the

late-glacial shore-line; genetically these dunes are strictly inland dunes as having been driven by inland winds, although formed at the emergence of the sandy deposits from the sea.

The conditions at the present dune-belts along the shores are thus not com-

parable to those which once occasioned the ancient dunes; and therefore a close

description of the shore-dunes would be of little interest for this study. I refer to the papers of Nilsson (1905), Leiviski (1905) regarding the Swedish and the Fin- landish coast-dunes respectively, and to the papers of Steenstrup (1894), Jessen (1918), and Warming (1907-1909) regarding the Danish ones, and also to the

descriptions to the geological maps of the dune-bearing coast-regions published by the Geological Surveys of these countries.

There are, however, instances of recent sand-drift although, on a minute scale, even at some places in the interior, which should be mentioned.

Recent dunes, all of them of an inferior size compared to the ancient ones, are occasionally met with within the mountain region of Northern Sweden.

The signs of wind-erosion to be noticed on the surfaces of stones in the high- mountains are due to grinding by finer dust-particles and do not bear evidence of true sand-drift (cfr A. G. Hbgbom, 1906, p. Ib69).

In the interior of Norrland there is known no ordinary sand-drift at all, except at some places where sand is locally made free by eroding rivers or by the tapping of lakes or other action of man. One instance of the latter kind is to be found in the very northernmost corner of Sweden, where in the year i905 the inhabitants made the little lake Arpojaure cut through the glacifluvial barrier


which formerly dammed it up. Ahlmann (1914, p. 512) describes the aeolian action on the dried-up bottom of the lake as follows: ~> The wind-erosion on the dried areas of the Arpojaure basin is rather great and has already formed considerable dunes, though the sand-drift can only have any effects from June to

September, as during the rest of the year the area is frozen and covered with snow. All the dunes are situated on the south and south-east shore>. The same

locality is later on described and mapped by Caldenius (1922), to the work of whom I also refer regarding geological data.

By a similar artificial cutting through of the damming barrier the former Ra-

gunda lake I796 was catastrophically drained, and the new conditions called forth

sand-drift, which, however, in this case was due to the river-erosion on the former lake-bottom. The aeolian action has resulted in a dune-string running parallel to the river on its north-east side. The principal dune has an altitude of 5-7 meters. On its lee-side a minute accumulation of loess takes place (A. G. H6gbom, I899. p. 93).

The instances of recent dune-drift called forth by deforestation are few. One is from Ovre Soppero, not far from the ancient dunes at Tulusjiirvi described

above, where between the scattered houses of the village some two or three wide

aprons of sand indicate the beginning of dune-drift At Hand6l in Jiimtland on the delta of the Handol river some small dunes are

to be found, and occasionally strong westerly winds seem to cause sand-drift on

parts of the delta which are destitute of vegetation. In Middle Sweden the few occurrences of recent dunes are yet more insigni-

ficant. Besides those already mentioned in the neighbourhood of Siter, there are some small ones at Avesta fed from the brink of the Dalilven.

Besides the dunes mentioned south of Billingen (p. 172), which at least partly have been in an active state in later times, there are also other occurrences of recent sand-drift on a small scale in the interior of South Sweden. They deserve to be mentioned on account of their situation within a tract of Sweden where the rainfall is particularly great, thus showing that other factors than humidity, as

sand-supply and winds may be decisive for the sand-drift. In Sm'iand some three km north of Lake Bolmen there is a little sand-drift field,

Slatt6o Sand, with an area of about 200oo acres, parts of which, however, have been forested during the last decades. The sand-drift is of comparatively recent date, as old documents show that the breaking through of the vegetation commenced in the beginning of the 18th century, and that in the beginning of the 19th century it caused the greatest trouble to the peasants (Wibeck, 19o6, Palm, i9I9). Also this sand-field seems to have been called forth by deforestation.

From the west-side of the Scandinavian ice-shed no ancient dunes are known. On the other hand recent sand-drift takes place near

Roros. According to the

176 IVAR HOGBOM

notices of Bjorlykke (1913), oses and glacial sand supply the material for the drift. Where the material is finer, its capacity of keeping the humidity prevents its blowing away, so that tabular deflation witnesses remain. The area from which the ling- covering is torn away is about one square kilometer (Thekla Resvoll, 1906. Cfr also Holmsen, 1915, P1. X.) It is to be supposed that this sand-drift, in some

way or other, is caused by the action of man, probably by deforestation in connection with the works at the neighbouring Roros Mines. Tradition also says that the area formerly was covered by dense pine-forest. (Holmsen, 1915, p. 172).

In the description of Tanner of the quaternary deposits of northern Fenno- scandia, no notices of recent sand-drift of any importance are to be found. In some cases, however, he notes deflation on the ose-ridges, and this may also be seen on some of the photographs which he reproduces (1914, pp. 257, 418).

Regarding the conditions in the Salpausselkt moraine-belt Leiviska says (1920,

p. 250): ,Kleinere Flugsandstrecken, wie wir ihnen auch tiberall an den heutigen Kiusten begegnen, wo sandige Aslandschaften an das Meer vorstossen, erscheinen an den sandigen Lokalitaten des Salpausselka ganz allgemein, obwohl sie infolge der Wald- und sonstigen Vegetation sich leicht der Beobachtung entziehen. Da und dort hat sich der Sand an den Strassen und an anderen Einschnitten von neuem in Bewegung gesetzt.>

Finally, as mentioned, Rosberg has stated that dune-drift on a small scale is

going on at places in Karelia, where probably the sand was accumulated as dunes already outside the border of the land-ice, when it was leaving the Sal-

pausselki stage.

CHAPTER III.

Dunes South of the Baltic.

Throughout Germany, Poland, and parts of the Baltic States, in the peripheral parts of the once ice-covered region and even a little beyond it, there stretches a broad zone within which ancient dunes are of common occurrence. In regard to both distribution and regularity of development the dune-formations in these

regions are far more striking than the comparatively insignificant corresponding formations in the Scandinavian countries. Under such conditions, of course, the dunes and their problems have been noticed much earlier by German geologists, and, all things considered, one may rather be surprised that the opinions about their origin and history are still so divided. This is chiefly because the contributions offered have mostly been of a more or less sporadic character and thus have not, even in cases where they have been of real importance, won the ne-

cessary attention, and because no systematic and detailed investigations into their

morphology and formative conditions have been performed.


As early as I832 K16den (cfr Solger, I9Io, p. 157) described the dunes at

Baruth in Mark Brandenburg and recognized them as such. Kl6den, however, thought that they were formed on an ancient shore, and that a longitudinal, particularly prominent dune-branch had the character of a Nehrung.

Since that time the dunes and the dune-sand have been mentioned a great many times, for instance in the descriptions appended to the geological map-sheets, but no generally applicable theories of their origin - at least none of such importance that a review in this place would be justified - have been formed in that connection. Some details given in the map-descriptions, however, are worthy of notice and will be mentioned in the subsequent description of different fields.

Later on, however, a lively discussion on the problems of the ancient German dunes was brought about by Solger, who I905 advanced his hypothesis on the

genesis of the dunes, according to which they have originated in a periglacial situation by easterly winds, called forth by a pressure maximum over the land- ice in the North. The interpretation of the basal forms of the dunes on which

Solger bases his hypothesis has been unfavourably criticized by later writers on dunes as Lehmann (1907), Jentzsch (1908), Keilhack (1917), and, as regards the Polish dunes, by Lencewicz (1922); especially the two lastmentioned authors have set forth a very strong and decisive criticism.

On the other hand, there are writers who are essentially of the same opinion as Solger.

Walther (1912, p. 320), for instance, gives an account of the conditions causing dune-formation outside ice-covered regions and seems to agree with the conception of the Middle European dunes as periglacial. In his >Lehrbuch der Geo-

logie Deutschlands> (1920, p. 333) likewise he speaks of the dunes as well as of other desert-phenomena as follows: >Die jetzt bewachsenen Diinen der Dres- dener Haide und die tausenden von erratischen Bl6cken, welche, zu wunderbaren Dreikantern geschliffen, bis zur Siidgrenze der nordischen Vereisung umherliegen, erinnern uns an die furchtbaren StUtrme, die wihrend der interglazialen Steppen- zeit das vegetationslose Gebiet von Mitteldeutschland bearbeiteten>.

Besides Solger, Tutkowsky (1912) has made the the most important contribution on this side. Like Walther, however, he wiews the dune-problem chiefly from a climatological standpoint and only briefly touches upon the question how far this interpretation agrees with the morphological evidence offered by the dunes about the prevailing direction of wind at the time of their formation; that he also regarding the basal forms of the dunes holds an opinion similar to that of Solger is evident as he uses the expression >postglaciale Barchane> (1912, p. 365). Solger, on the other hand, endeavours to find evidence in the shape of the dunes for his hypothesis of their periglacial character and their formation

by easterly winds. In the subsequent pages I shall have an opportunity of re-


178 I V A R H O GGBO M

verting to this hypothesis and advancing the facts which seem to me decisively to prove its erroneousness.

Keilhack (1917) arrives at the conclusion that the dunes were formed during the Ancylus- or Litorina-age and that their shape proves that they were formed

-,

so

drr

2

0-200km

Fig. I17. Dunes south of the Baltic, Western part. Marginal drainage channels shaded. Dune-fields black: i Veluwe; 2 Frankfurt; 3 Wittemberge etc.; 4 North of Berlin; 5 Luckenwalde-Baruth; 6 North-

west of Rothenburg. According to Keilhack (1917) and, for Holland, van Baren.

by westerly winds. The paper of Keilhack is the most weighty contribution from the German side, and beyond doubt his views will on the whole obtain

general recognition. Nevertheless, I have found it necessary to dwell in the

following pages on certain hitherto neglected morphological features of the dunes, which in my opinion have not been sufficiently accentuated by Keilhack.


A review of the most important contributions to the knowledge of the German

inland dunes is given by Wahnschaffe-Schucht (1921, p. 423), which authors

themselves maintain that the dunes have been formed in Ancylus time by west-

winds.

V

Maloof rsaw - Al

a . . . . . . . . . . .

Fig. 18. Dunes south of the Baltic, Eastern part. Marginal drainage channels shaded. Dune-fields

black: 7 Warthe-Netze; 8 Thorn; 9 Puszcza Kampinoska; io Upper-Bug; II South of Pripet.

According to Keilhack (1917) and Lencewicz (I922,),

The latest investigations of Middle European dunes have been made by Lence-

wicz, who has treated the Polish dunes. Like Keilhack, this author regards it as quite obvious that the dunes have got their shape owing to the action of west-winds and exposes the misconception which has originated the false conclusions of Solger in this regard. How many different interpretations the Middle

180 IVAR HO GBOM

European dunes have given rise to, however, is illustrated by the fact that Lencewicz does not regard them as representing vfossilv forms and the climate of times past, but thinks that they have been wholly or in part formed and still are being formed under the climatic conditions now reigning.

Dunes in Germany.

Regional distribution. The map accompanying Keilhack's paper (1917) for the first time gives a full idea of the extensive regional distribution of the dune-fields in Germany. Both in the paper itself and on the map Keilhack points out the close connection between the glacial border drainage channels, the >Urstromtalers, and most of the dune-fields. He gives the following survey of the geographical distribution of the dunes:

>Die Ubersichtskarte zeigt als erstes wichtiges Ergebnis, dass die grossen Diinengebiete Norddeutschlands im wesentlichen an die breiten diluvialen TalzUige gekniipft sind, sowie an die mit ihnen in engem genetischem Zusammenhange stehenden, ihnen eingeschalteten Staubecken, und an die ebenso eng mit ihnen

verkntipften ausgedehnten Sanderflichen. Da letztere ebenfalls mit den Talsand- flachen vielfach so eng verbunden sind und in ihren Oberfliachenformen ihnen so ausserordentlich gleichen, dass eine Abtrennung vielfach mit grossen Schwierig- keiten verkntipft oder ganz unsicher ist, so habe ich einen Teil solcher talartigen Sandergebiete in der gleichen Weise dargestellt wie den Boden der Urstromtaler selbst. Auch sie sind mehrfach Trager ausgedehnterer DiInengebiete. Da, wo wir Diinen auf den eigentlichen Hochflichen sehen, wie vielfach in der Umgebung von Berlin, machen wir fast immer die Beobachtung, dass sie sich selten weit von solchen diinenreichen Tilern, Becken und Sanderfl•achen entfernen. Die wenigen Ausnahmen k6nnen nur als Bestatigung der Regel dienen. Ungeheure Gebiete sehen wir frei von grossen Diinengebieten, nimlich alle grossen Hochflachen im Norden und Sliden des Netzes unserer Urstromtiler sowie die grossen Hoch- fliacheninseln innerhalb dieses Netzes. Die in der Karte Weiss gelassen und damit als frei von Diinen bezeichneten Flichen sind dies natiirlich nur in dem Sinne, dass grosse zusammenhingende Flugsandgebiete darin fehlen. Die untere Grenze fir die Darstellung der einzelnen Diunengebiete habe ich bei Massen von einer halben bis einer deutschen Meile angenommen; da aber, wo kleinere Diinengebiete in sehr grosser Zahl auf engem Raum auftreten, sind sie zusammengefasst und in der Karte als einheitliche Fliche eingetragen worden. Hitte ich alle kleinen

Einzeldiinengebiete mit aufnehmen wollen, so ware das Bild von einer erdriickenden Fiille von Duinen besetzt erschienen, und jede Ubersichtlichkeit wire verloren

gegangen.> Keilhack calculates that the dune-bearing regions form some 5 % of the area


of North Germany, if those fields are also reckoned which are too small to be shown on his map.

Only one large dune-bearing district in the interior of Germany is not connected with the >Urstromtiler> namely that south of Frankfurt am Main, the dunes there being built up from the fluviatile deposits of the Rhine valley.

The regional distribution of the German and Polish dune-fields has greatly influenced the discussion of their age and formation. The fact that they are most abundant in a region with periglacial position during the time when the last land-ice melted away from Germany and the Baltic lands, might naturally be interpreted as due not only to the existence of large sand-deposits within that zone, but also to special climatic conditions near the ice-border. In fact this

supposition has led to the theory of a periglacial formation of the dunes put forth by Tutkowsky (1912) and others. Certainly even for Solger (1905, I9 io) the situation of the dunes at the former ice-borders has been ultimately decisive, although in the shape of the dunes he sees evidence of periglacial east-winds; and starting from this supposition he formally founds his conclusions as to the

age of the dunes on his interpretation of their morphology. Because of the explicit description of the geographical distribution and geo-

logical position of the German dune-fields, given by Keilhack, I refer to his paper for further details which do not appear on the map or from the above quotation. Only regarding some circumstances which may influence the climatological discussion in the final chapter of this treatise, I will later on call attention to some further facts of importance.

On the other hand, Keilhack only very summarily touches upon the morphological problems of the dunes. In order to maintain the uniformity of my treatise, however, I have found it necessarry to give special descriptions of some of the German fields. Besides, a study of some traits in the morphology seems to me also to elucidate even other climatological questions than that of the direction of the dune-driving winds.

There can hardly be any doubt that all the large dune-fields connected witl/ the border drainage channels are formed during the same epoch. Even their

geographical situation makes this probable, but above all it is proved by the

extraordinary similarity in their morphological development. In some cases, however, more or less isolated dunes are to be found, the orientation of which

may possibly indicate other formative conditions. If due regard is paid to these

exceptions, a detailed examination of a great number of fields would thus hardly yield any new results beyond those obtained by the examination of a few characteristic ones. In the sequel I therefore intend to limit the descriptions accordingly. The general difference which lies in the greater size and finer development of the

182 IVAR HO0GBOM

dune-fields, the further east one goes in Germany, I shall have an opportunity to touch upon when discussing the climatic conditions of dune-formation. As the dunes are far better developed in the eastern than in the western regions, though there is no essential difference as to their morphology, I shall chiefly dwell upon the former, as earlier writers have done. Even round Berlin and south of it well-

developed and instructive dune-fields are to be found, so it is really west of that district that the dune-formations can be said to be palpably less instructive.1

In the following description of the German dune-fields, I am first giving a

survey of some of the most characteristic ones in the central and eastern parts of the >Urstrom>-region in order to form a conception of the main morphological features; afterwards I shall also dwell upon some of the fields which are more

exceptional as to the situation or to the development of the dunes. As widely diverging opinions have been put forth regarding the age of the German dunes I shall finally dedicate some pages to a review of these questions before extending the description eastwards to the dunes of Poland and the eastern Baltic States.

One of the few German dune-fields which lie within geologically detail-mapped regions, is that falling mainly within the geological sheet Gr. Schcnebeck. This dune-field has a greatest width of 7 km and a length of 20 kin, and extends

lengthwise about WSW--ENE. The dune-formation covers the whole width of the broad sand-girdle immediately outside the range of the end-moraines, which bends here locally in a more northerly direction. West of the dune-bearing field follow, a little lower situated, marginal drainage channels and alluvial formations. The dune-bearing sand-plateau rises slowly to the east, the most westerly dunes

lying at about 55 m, and the most easterly ones at 65 m above the sea. The dunes and dune-complexes are chiefly U-shaped and open towards the

west; the wings, however, are often very elongated, so that in parts of the field the longitudinal forms are most prominent (cfr Fig. 19). Here as elsewhere in

1 Continental dunes of the same type as those in Germany, described below, have not as yet been recorded from Holland, but probably further investigations will reveal their existence. Thus Prof. J. van Baren, to whom I am indebted for informations regarding Dutch dunes, writes me:

,Continental dunes of probably glacial time and then built by easterly winds are to be found, as I think, near

Apeldoorn [Veluwe], but an exact proof has not been given till nowD. Other inland dunes are met with at several places in Holland, but they have been formed after that the vegetation, forests and heaths, has been destroyed by man in praehistorical or historical time, because of which they do not bear any direct evidence as to the climatic development. At many places vegetative fixation has not been restored and sand-drift is still going on (cfr also Keilhack, 1917, p. 5). It is remarkable to note that a re-opening of the dune-fields has so easily taken place just in Holland where the climatological conditions for sand-drift must be comparatively unfavourable. It indicates that the binding power of the

vegetation always is very sensible for outside influences even if it otherwise fully prevents all sand-drift, and that a humid climate not necessarily is a hindrance to sand-drift on dune-fields already existing.


Germany, however, these have not the character of garmadas, but are to be considered as relict wings, remaining after the central parts have wandered further. Nor are there any fully developed wind-furrows, and >)Kupsten>> forms are also

missing. The dunes here met with can in fact be regarded as an extreme type of the different kinds of bow-formed and horseshoe-formed dunes in Germany. They

>

"p

600

=200

Fig. 19. Dunes in the Gr. Sch6nebeck Forest. According to the geological sheet >Gr. Schbnebeck'.

are in many respects suggestive of dunes from present half-fixed regions, but there are important dissimilarities, in the first hand manifested by the fact that the longitudinal forms extend wind-wards and not lee-wards from the transversal

ones, wherefore it seems that it is hardly possible to ascribe the nature of these

disjointed horse-shoe dunes to the influence of vegetation. Characteristic of

secondary sand-drift in all imperfectly bound dune-fields seems, on the contrary, to be the occurrence of rather capricious breaches, causing either irregular

>>Kupsten,>-formations or a breaking through of the dunes with ensuing garmadas

on the lee-sides. There are also some other fields (cfr Fig. 24) which are

distinguished by too geometrical a development to be ascribed to secondary deflation of dunes in a half-bound condition. Another explanation seems then to lie nearer at hand, namely changes in the sand-supply, which, as already

184 IVAR H 0 G BOM

mentioned, affects the development of the dune-forms. Such changes are indeed to be expected, since the vegetation must first take possession of the lower, plains, from which the sand is blown to the dunes, while the dunes themselves, and particularly their highest parts, are the last to be fixed by vegetation. Hence it is deflation, not as previously accumulation, that has become decisive for the

development of the dunes. The equilibrium which formerly prevailed, and which has given rise to transversal dunes, has been disturbed, because the sand-supply has given out or been reduced; thus the shape of the dunes does not answer to the new conditions and thus is subjected to re-arrangement.

Some 20 km south of the Gr. Sch6nebeck field, that of Eberswalde is met with. Although in many respects less model-like than in some fields farther to the south and east, the Eberswalde dunes essentially present the common regular system of consecutive horseshoe-ridges, which will be further described and illustrated from other localities. The profile Fig. 2o which I have measured at this field can be regarded as fairly representative as to the average regularity of such a train of dunes.

Besides the occurrence at places of a beginning breaking through on the dune-

ridges, which seems to be rather uncommon elsewhere within fields of this type, another probably secondary trait in the dune-morphology should be mentioned, which has also been duly noticed by Solger. Some of the southern-wings of the horseshoe-dunes show namely a more gentle slope towards the south and a steeper slope towards the north contrary to what would be expected. This feature of the dunes is by Solger interpreted as a detail in the general reversal of the dune-

profile (cfr below) due to the change in the wind-direction from the by him

supposed periglacial east-winds to the present west-winds. Also from the point W E

Fig. 20. Section of a series of dune-bows at Eberswalde. Length of the section I km. Heights twice exaggerated.

of view of the hypothesis of west-winds as having originated also the ground- form of the dunes, this abnormal development of the dune-wings may be regarded to indicate a change in the wind-direction at the end of dune-drift time, namely from more due westerly to the present south-westerly winds. The special kind of

asymetry, which also can be traced on the basal forms of the dunes will be better illustrated by instances from other fields in the sequel.

One of the dune-districts of Germany which has of old been much noticed, is, as has been mentioned, that in the neighbourhood of Luckenwalde and Baruth


in the large marginal drainage channel some 5o km south of Berlin. In this

region, comprised by the topographical sheets Luckenwalde, Paplitz, and Baruth

(I :25,00ooo), there are two different, great dune-complexes, namely Schlage-Berge north of Neuhof (Paplitz sheet) and the one south-east of Baruth (Baruth sheet), and,

ckeawalde

*~ Mk- .~1

- " ....

... ?~yo --.Brt A .. • - ---- _. _-

Fig. 21. Dune-complexes at Luckenwalde-Baruth. After Solger.

besides, several scattered dunes, among which one or two longitudinal branches are particularly prominent owing to their length and size. The distribution of the dunes appears in more detail in Fig. 21 reprinted after Solger (g1910, p. 159).

There is a considerable difference between the two dune-complexes mentioned.

Schlage-Berge, which complex has a length of 6 km and a breadth of up to

1,2 km, shows a series of about 15 successive U-shaped dunes, the wings of

,41 K#--?:- 41 !011" 4, ?'4 N:?4 JV 7 i'_-'!%p It IL

17 WA I I-A.

t A Ir

It

Fig. 22. Dune-complex NW of Baruth (cfr >)Schlage-Berge>>, Fig. 21) Contour lines with 5 m

aequidistance accentuated. Scale I :5o.ooo. From Messtischbl. Paplitz.

which follow each other on a line forming a sharp limit towards the not dune-

bearing regions to the south and north. A certain asymmetrical development of the dune-segments, giving their central parts an oblique length-direction, appears in this field as well as in some others. The dunes reach a height of as much as 18 m and show a marked difference between the windward-side, gently declining

186 IVAR H0)GBOM

towards the west, and the lee-side, falling steeply towards the east. As generally is the case with horse-shoe dunes, a difference in the inclination of the sides is perceivable even where the wings show a bend approximately parallel to the

general direction of the sand-driving wind. A cutting of a dune at the high-road north of Neuhof shows an earlier over-

blown dune-side, Fig. 23. This is very uncommon within the dune-regions in Central Germany. If, on the other hand, recent sand-drift had been of any im-

-lit

Fig. 23. Cutting of a southerly dune-flank N of Neuhof. Photo towards the west. (Cfr Fig. 22.)

portance for the formation of the dunes, such intersections would of course be found very often, as well as tree- trunks etc. embedded in the dunes. Fig. 23 is therefore chiefly inten- ded to illustrate a rare

exception, which would in fact have been of general occurrence if the

theory advocated by Lencewicz in regard to the Polish dunes had been applicable to the German ones. Although the stratification within this cutting is not very

marked, it seems, however, to indicate wind-side accumulation from the north within the inner parts of the dune. On the other hand, the steepness of the overblown surface corresponds to that of a lee-side. This instance would thus illustrate also the reversal of the wind-side and lee-side, which, as mentioned, often can be noticed on the southern flanks of the horseshoe-dunes or on the southern rand-dunes in some complexes.

The dune-complex south-east of Baruth is typically V-shaped. The more complete deflation within the northern part of the dune-complex is sufficiently accounted for by the circumstance that the wind. has had freer play here than in the southern part which is sheltered by the higher ground windwards. It is proved by these two fields, lying so near each other in the same marginal drainage channel, that small differences in the topographical conditions directly, or perhaps indirectly by varying the possibilities for an interference by vegetation, may bring about considerable dissimilarities in the morphology of the dunes.


In this case the supposition lies nearest at hand that a more limited supply of sand has conditioned the V-shaped development of the dunes south-east of Ba- ruth.

In some places in Germany there are V-shaped dunes or dune-complexes with traces of an earlier and straighter dune-ridge between the ends of their wings. The best instance of this is to be found in the yet unpublished geological Liibben sheet south-east of the dune-fields last mentioned; among these, by the way, the

dune-complex south-east of Baruth exhibits a si-

milar, though not so di-

stict, development. The same phenomenon is also met with at other

places, for instance in the topographical sheet

Ziillsdorff( 25o000oo, N:o

2466). In am very much obli-

ged to Prof. F. Kaun- howen and the Geolo-

gical Survey in Berlin, for the allowance to draw the sketch Fig. 24

to

sit J Fig. 24. V-shaped dune-complex with remnants of a straighter bow-

formed dune-ridge between the flanks. From the geological sheet Ltibben.

from the rough draft map and publish it in this treatise, and I wish here to

express my most sincere thanks for this generosity. The development described affords another evidence that the typical V-shaped and

U-shaped dunes as to their basal forms also are the products of west-winds. On

the hypothesis of Solger it would hardly seem possible to explain the origin of

the girdle of dune-sand hills lying between the wings of a supposed barchan-

complex. In other respects it seems equally impossible to construct any simi-

larity between dune-complexes of this type and barchans. A small detail in the

development of the Libben dunes deserves to be pointed out in this connection.

Solger states (1910o, p. 164), as a strong support of his hypothesis, that the ends

of the wings converge towards the west in the Schlage-berge complex, and regards this fact as incompatible with the theory that they have been originated by west-

winds. In a couple of small dune-segments in the Liibben complex the same

phenomenon is to be observed, and as a matter of fact such a development is

not so unaccountable, if due regard is taken to the variations in the direction of

the winds.

188 IVAR HOGBOM

The Luibben complex, however, has its greatest interest in the indication it

gives of two different phases of dune-drift, a first one during which a straight or

only gently curved, dune-segment was formed, and a later one during which this

dune-segment has been blown asunder and a V-shaped dune or rather a V-

shaped dune-complex has been formed. Here a still more beautiful phenomenon appears of the same kind as that

already mentioned from Gr. Schbnebeck. The symmetrical development of the

complex is particularly striking; this indicates, still more strongly than was the case with the fields already described, that the later phase of the dune-drift has not been caused by attacks of the wind upon the irregularly distributed gaps left unshielded by an imcomplete covering of vegetation.

If, nevertheless, this morphology may be imagined to have been caused under the conditions offered by an incomplete vegetation, two alternative explanations present themselves. Either the transformation of the earlier bow-formed dune into the V-shaped complex denotes the last stage in the dune-drift when vegetation has already got a hold, or it denotes a new period of sand-drift which has commenced since the dunes from the first period have become fixed by vegetation. I shall have an opportunity of touching upon this question later on.

It should be added that in a preliminary report on the field work for the Liibben and Luiibbenau sheets Kaunhowen (1916 p. 526) gives the following inter-

pretation of the genesis of the dunes: >Recht weite Verbreitung haben von den alluvialen Bildungen noch die Diinen.

In den weiten Talsandflachen zu beiden Seiten des Flusses, besonders auf seinem rechten Ufer, treten sie in grosser Zahl, bald als scharfe, sich oft einige Kilometer hinziehende Walle, bald als hohe Riucken, bald als ausgedehnte wild kuppige Partien auf. Die langgestreckten, schmalen Diinenwialle sind namentlich auf dem rechten Ufer des Flusses in der Bbrnicher Forst verbreitet. Die Spiel- und

Pfaffenberge westlich bezw. nordlich von Liubben, erheben sich je 15 m (65,6 m+ NN), die Schusterberge bei der Oberfdrsterei Bbrnichen (alles reine Flugsand- bildungen) (63,5 m) rund I13 m tiber dem Talsandboden. Die Schiittrichtung ist verschieden: Die meisten Diinen, namentlich die schmalen, langgestreckten Wiille 6stlich des Flusses, verdanken siidlichen Winden ihren Aufbau; zuweilen ist auch die Wirkung westlicher Winde erkennbar. Auch die Schusterberge sind im all-

gemeinen durch siudliche Winde aufgeschiittet; nur ihr h6chster Kamm zeigt n6rd- liche Windwirkung. Auf dem linken Flussufer herrscht gleichfalls die Wirkung siudlicher Winde vor; doch tritt daneben auch hiufiger die n6rdliche Windrichtung hervor?.

From this quotation it appears that Kaunhowen gives an explanation of the

morphology of the dune-complex in the B6rnicher Forst which altogether differs from the one that I have given above. Kaunhowen has probably based his


conclusions substantially on observations of the

dune-profiles at different places, and not upon the development of the basal forms, which

perhaps were not mapped at the time of his memoir. It is interesting, however, to note that Kaunhowen finds evidences for south-winds on the long west-east dune-ridges. This seems to indicate that a similar overthrowing by later winds has taken place here, as was already mentioned above with regard to some of the dunes north of Berlin.

In the southernmost of the large marginal drainage channels there is an extensive dune-field north-west of the town of Rothenburg (Ober- Lausitz). The finest part of the dune-field, which lies between the Spree and the Neisse, is found in the schematical sketch Fig. 25 drawn according to the topographical sheets Niesky and Koblfurt

(I : 100,000). As is the case in most of the fields extend-

ing in the direction of the wind within the region of the marginal drainage channels, the eastern dunes lie considerably higher than the western ones. Thus the dunes denoted in Fig. 25 west of the Spree are situated at an altitude of about

125 m while the easternmost ones near the Neisse lie about 150 m above the sea. Only to a very small degree, however, can this be attributed to aeolic accumulation but must essentially be due to the prae-existing topographical conditions.

That dunes are lacking around Nochten, on the other hand, is probably due to deflation, the dune-drift having ceased, either because the level of the ground-water was reached or because a film of lag gravel was formed. Such deflation areas to the west of the great dune complexes and often enclosed within marginal dune-tracks or longitudinal ridges are as fact very common also at other fields, e. g. those of Warthe-Netze and Thorn (cfr below).

<. <

(lA

AP

opt

400

fI '"

Cl-

CA

7z

b

I.-:

?114

(lj-

6z

b5

190 IV AR H O GB O M

The present ground-water level lies very near the dune-bearing surface. Thus the map denotes that there is swampy ground not far from Nochten, and there are likewise some characteristic small lakes in the valleys between the easternmost dune-segments of the field. They have no superficial outflow and are dammed up by the long southern rand-dune. On account of the small scale they have not been drawn in the map Fiog. 25.

The asymmetrical development, which is especially striking in the eastern part of the dune-complex, is to be noticed also in other

regions, though generally not so marked. This is the case, for

instance, with the Schlage-Berge complex described above and re-

produced in Figs 21 and 22. This

asymmetry finds expression in a

tendency to a fusion of the southern

wings of the dunes into one dune-

ridge, while the left ones lie free of each other. This development is certainly to be ascribed to the

topographical conditions, for it is

striking that in the places where it is most pronounced, the dune- field borders on the south on low, marshy ground; the right dune-

wings, therefore, have been ham-

pered in their development, which has not been the case with the left ones bordering on drier

ground. It is also possible, however,

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that the asymmetrical reversal of the lee-sides and windward-sides of the wings to the north during the last stage of dune-drift has in certain places been of im-

portance for this development.

One of the greatest and most instructive dune-fields within the >Urstromtilera is that situated between the rivers Warthe and Netze on both sides of the present (1923) German-Polish frontier.' Lehmann (1907) has given a description of this field, and due attention to its importance has been paid also by later writers on the German dunes, specially by Solger (19i10).

Because of present political conditions I have had to refrain from visiting this field as well as those lying farther to the east. The following description is thus based upon studies of the topographical maps, in the first place of the excellent German >Messtischblitter> on the scale of I : 25,000 , besides, I have made use of some of the notices given by Lehmann (1907), to whom also refer further particulars regarding this field.

The map Fig. 26 represents the main dune-field; in its prolongation both to the west and to the east, however, there exist smaller dune-fields or scattered dunes. The dunes of Czarnikau, which will be mentioned later on, are situated north of the eastern part of the map, on the northern side of the river Netze. The total length of this dune-region, which begins at the Oder and continues almost to the place where the Warthe, coming from the south, bends to the west, is about 150 km.

The Warthe and the Netze, running parallel to each other and on each side of the dune-bearing plateau, both follow the northernmost >)Urstromtal> to the WSW. The Warthe runs close to the dune-field, whilst the Netze is separated from it by a dune-free zone some io km wide.

On the map I have schematically separated, by a dotted line, the low and flat

drainage valleys of the rivers from the older glaci-fluvial plain. The western part of the latter is practically free from dunes and has the character of a deflation area. The topographical maps in fact indicate a very insignificant, although characteristic undulation of the surface, with the forms extending west and east. There is a slight rise from these western parts of the field and to the easternmost

dunes; the altitude of the former is about 40 m whilst the latter lie at about 62

m. The level of the river Warthe lies in the east at about 35 m and in the west at about 20 m above sea level.

1 For the sake of convenience I prefer to examine here as well the parts of the dune-region in question which are situated within present Poland.

2 The main dune-area is enclosed within the sheets (Messtischbliitter I :25,ooo): Gottschim (1707),

Altsorge (1708), Schneidemtihlchen (1709), Neubrtick (I7Io),

Schwerin (I778), Waitze (1779), Birnbaum

(1780), and Zirke (1781).

192 IVAR HOGBOM

The central zone of the main dune-field (Fig. 26) is some 8 kms wide and is characterized by a horseshoe-formed strike of the dune-ridges, which are

forming a dense net-work. In the middle of the zone the dunes are only slightly bow-formed, turning the concave side towards the west, whilst near the borders of the zone the deviation of the ridges towards the west is almost complete, the dune-flanks, especially at the southern border, joining each other in the same manner as already described from the Luckenwalde-Baruth field. At the latter

place, however, most of the dunes run from one border to the other presenting uninterrupted horseshoe-forms, whilst at the Warthe there is a swarm of transversal

ridges arranged according to the general horse-shoe striking across the field, the individual dune-ridges attaining a length of only one or two kilometers. The dunes in the middle of the field, therefore, have a true transversal character.

Naturally, a case of strictly parallel dunes is not in question, in fact they show

everywhere ramifications and garlands, but always with a general common trend. The dunes show well developed wind-sides to the west and lee-sides to the east, the slopes of the former according to Lehmann (1907, p. 358) averaging 30-8' and of the latter 250-3o'. The usual height of the dunes is about 20 m, but much higher ones are often met with; in the western part of the field there is in fact one dune which reaches 43 m above the plain. Also amongst the easternmost dunes there are some ones which attain heights of 30 m and even somewhat more. Counting with 20 m as an average for the heights of the dunes, Lehmann calculates that the total mass of sand within the dunes amounts to 6oo to 8oo millions m3. A section along the middle of the zone would show about

60 ridges at average intervals of about one kilometer. A comparison between the Luckenwalde and the Warthe fields indicates that

the horse-shoe form and its dimensions are dependent on the breadth of the dune- field. Where the field is wide enough, horse-shoe dunes do not develop, as a rule, but garlands of gentler bow-forms and deviated flank-dunes are to be found only near the borders of the field. This is also well illustrated by the morphology of the Mora-field in Sweden, described in the previous chapter. Within the central zone of the Warthe field, however, there are some exceptional horse-shoe dunes, but they seem to be found only at places where the ridges lie less close to each other and thus a more individual development has been possible.

Outside the main dune-zone, and particularly on its southern side, on the some three kilometers broad strip alongside the Warthe, on the other hand, there are horse-shoe dunes and longitudinal ridges of quite another type than the transversal dunes of the interior of the main-zone. Some few of them are of the type described from Luiibben, showing remnants of a primary, straighter bow between the flank-ends. The best developed one is to be found on the Neubriick sheet. It is noteworthy that these forms are situated at the borders of the field and not in


the center of it. If they had been due to sand-drift when the field was partly fixed by vegetation, one would have expected that the higher situated and drier inner parts of the field in the first place would have been exposed to the attacks of the wind. Also this example, therefore, seems to indicate that the dune-type in question is due to other conditions than those which are presented by an in-

complete covering of vegetation making a partial reopening of the dune-drift

possible. Also on the north-side of the main dune-zone there are similar longitudinal or

horseshoe-formed dunes, although less numerous. It is interesting to note, that Lehmann does not regard any change in climate

as necessarily evidenced by the existence of this mighty dune-field. Now it would seem that the further east the fields are situated which have been studied by the several scientists, the more these have felt inclined to give a quite actualistic ex-

planation of the formation of the dunes. So it is with Lencevicz regarding the Polish dunes and Cholnoky regarding the Hungarian ones. On the other hand, those scientists who mainly have had their attention fixed upon the Middle Ger- man dunes make usually no mention of such an eventuality that the present climatic conditions would make a dune-drift possible on the scale evidenced by the ancient fields. In accordance with this is the fact that from the western fields

hardly any notices are given regarding possible recent sand-drift. Of the WVarthe- Netze field, however, Lehmann says (1907, p. 375): )iNahmen wir die Forstbe- amten aus dem Zwischenstromlande weg, giben wir Streunutzung und Herden- trieb frei, dann wilrde Misswirtschaft, unterstiitzt von einigen Waldbrinden, uns in Balde Bilder friuherer Ode wieder vor Augen stellen und ruhende Diinenkdmme zu neuer Wanderlust erwecken>.

Lehmann also, however, recognizes that there has been epochs of intenser sand-

flight, as he finds verified by the different types of dunes met with on the field, but he does not venture upon any opinion about the age to which they correspond.

Not having any personal knowledge of the field, for my own part I feel inclined to judge that the Warthe-Netze field and also those farther to the east have

got their main features not during present climatic conditions but during the same

epoch when the dunes on the western fields were built up. However, it seems undeniable that accidental reopenings of the sand-flight in historical time on some

places in these fields have not been uncommon. This is in fact also made probable by the topography of the dunes as shown by the detailed topographical maps (1:25.000) on which the dune-ridges at places appear far less regular than on the fields farther to the west.

Lehmann gives the result of mechanical analyses of 12 samples from the field, from which it appears that the sand is unusually fine-grained. The averages of his figures are as follows:

13 Geograishka Annaler 1923.

194 IVAR HOGBOM

Size of the grains in mm.: 2-1 1-0.5 0.5-0.2 > 0.2

12 samples from the Warthe field ...... 0.2 4.8 37.9 57.-

Furthermore, Lehmann states that within some of the dune-complexes the sand is finer in the eastern dunes which have wandered a greater distance than in the western ones. He seems, however, not to have found any regular increasing in the size of the sand eastwards within the whole field. If this is not due only to the samples being too few, it would indicate that the easternmost dunes have not wandered further than the other ones, but that the dunes have originated more or less evenly over the whole field.

The Warthe-field shows many interesting hydrographic features, some of which

may be mentioned in this connection. Within the central parts of the main dune-zone there are some small pools

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Fig. 27. Brook eroding backwards in the dune-

plateau, Scale I : 25.00ooo. From Messtischblatt

Zirke.

without outlet, showing that the ground- water level lies near the surface of the

dune-plateau. Outside the main dune- zone there are several small lakes, most of them long and narrow and extending at right angles to the direction of the field and the rivers. The lakes situated south of the dune-zone have outlets to the Warthe, whilst the outlets of the northern ones run to the Netze. Their most remarkable feature is perhaps that the basins seem to be of younger date than the dunes, as at some places the more or less longitudinal dune-ridges continue on both sides of the lake. A closer examination of the work of some backward eroding brooks seems to indicate the origin of these basins. These brooks have eroded broad and very shallow channels with a flat bottom. This shape of the channels is most probably due to lateral backward erosion caused by the oozing out of ground-

water above an impermeable layer of clay of which Lehmann speaks, perhaps combined with a solifluction.

The basins of the long and narrow lakes - which according to Lehmann have a maximum depth of 4-5 m - seem to me to be such channels, which have


been separated from the river by the growing up of marsh-vegetation. The latter is probably a consequence of the elevation of the river level because of sedimentation, which has also caused a general elevation of the ground-water level and the filling up of the basins. That really a considerable sedimentation has taken place appears from the profiles from the Netze valley mentioned below.

Lehmann, on the other hand, regards the basins of these lakes as channels of the melting-water from the land-ice; this, however, to me seems incompatible with the statements made above.

In this connection the speculations of Korn (1918) regarding the dune-field at Czarnikau and its hydrography should be mentioned. This comparatively small

dune-field, which has a length of Io km by a breadth of 2 kin, is situated at the northern border of the Netze valley, where at Czarnikau the Netze, coming from the north, bends to the west. The dunes are longitudinal or horseshoe-formed and oriented like those north of the Warthe. Korn has in particular had his attention fixed on the depressions between the dunes which he regards as aeolian excavations in the dune-bearing plain. These depressions are overgrown with peat-bogs to a

depth of more than two meters. According to Korn, the volumes of the depressions beneath the surface of the peat exactly equal the volumes of the dunes on their east-side and he concludes from this that each dune has been fed by the material blown out from the nearest depression. This coincidence is not found between the depressions and the respective dunes lying on their west-sides, and therefore Korn concludes that the dunes have been driven by west-winds.

Although of the same opinion regarding the direction of the dune-driving winds, I cannot accept Korn's reasoning. He himself emphasizes the fact that the filling up of the depressions by peat is due to a rising of the ground-water level after the dune-drift time. Under such circumstances the relative volumes of the peat- covered depressions and the dunes, being dependent on the present ground-water level, have nothing to do with the genesis of the dunes.

In connection with his hypothesis of the relation between the depressions and the dunes, Korn gives some interesting data regarding the alluvial accumulations in the Netze valley. In several excavations which have been made for the purpose of some embankment works he has ascertained the existence of alluvial deposits to a depth of I 2 m below the present bottom of the broad valley. Down to that

depth the sand contains humus, whilst below it the pure diluvial sands begin. Korn ascribes this filling up of the old valley to the rising of the erosion-base, that is the level of the Baltic Sea since the Ancylus time. This explanation seems

hardly satisfactory, as it postulates that the river in the Ancylus time had practically reached the ripe stage enabling a continual upheaval of the valley-bottom by sedimentation from the mouth and up to this region. On the other hand, a gradient

196 IV AR H O GB O M

in the sinking of the land may have caused new possibilities for sedimentation within the drainage system.

It is highly interesting, however, to notice that such a rise in the level of the rivers has taken place, and that this may have been caused by other than climatic factors. The fact that marsh-ground occurs within the old sand-drift regions thus seems, at least in the cases in question, not necessarily to indicate a more humid climate nowadays than at the time of the dune-drift. In Sweden, on the other hand, where the changes of the sea-level have gone in the opposite direction the existence of pools or marshy ground amongst the dunes is naturally a positive indication of climatic changes.

Korn further reports the interesting find of stone tools and pottery of early Bronze Age within a dune on a layer which was overblown by sand, in parts to a thickness of three meters. The same layer he has also observed within other dunes. It thus seems as if a later less intense sand-drift, at least locally, had taken place, although the main forms of the dunes date from an earlier time.

The fields which have been treated on the preceding pages belong, both on account of size and regular development of the dunes, to the most instructive ones. Within some less extensive dune-occurences in North Germany there

are, however, dunes the development of which indicates that they have possibly been driven by other winds than the due westerly ones which have built up all the large fields.

This is the case, for instance, in the neighbourhood of Wittemberge in the Elbe

valley. Thus, in the description appended to the geological Rainbow-sheet it is stated that the dune-banks run mainly in a west-east direction, which is taken as a sign of their having been driven by either north-winds or south-winds. From the topographical denotation in the sheet, however, nothing is to be gathered regarding the shape of these dunes.

In the next sheet to the south, Schnackenburg, there is stronger reason to

suppose that during some epoch north-winds have been driving, since a couple of dunes seem to have been driven out from the large sand-field to the north on to the >Schlickv, which takes up the central and southern parts of the sheet. This circumstance is also noticed in the description appended to the map.

It should be mentioned, however, that this development of the dunes is not

general for the region, on the contrary also on the lower Elbe the best developed dunes show the influence of westerly winds. This comes forth by Sabban's

(1897) description of the dunes on the north side of the river in the neighbourhood of Ludwigslust. This author finds in fact that the orientation of the dunes

corresponds to the nowadays prevailing south-west winds. To me it seems,


however, most probable that these dunes also will prove to have originally been built up by the same west-winds of which the other great dune-fields in Germany bear evidence, and that the west-east orientation, which Sabban mentions as

exceptional, rather is the original normal one, whilst the SW-NE orientation either is due to topographical conditions or to the influence of the winds in the

very last phase of the dune-drift in the same way as has been described above from other fields.

Within the sheets Cremmen, Marwitz, and Rokrbeck west of Berlin there are likewise dune-ridges extending mainly west-east. In the Marwitz sheet the topographical denotation indicates, besides, at least in one case, a wind-side declining more or less gently towards the north and a lee-side falling rather steeply to the south.

In all these cases the dunes are comparatively insignificant in size and also of irregular shape. To a certain extent this impression may be strengthened by the somewhat old and defective topographical basis of the maps, but there is in

any case no doubt that the dunes are not nearly so regularly developed as the

generally occurring west-wind-driven dunes. On the other hand, at least part of them may hardly be considered as the remaining, disfigured wings of these, because, as already mentioned, their situation in relation to the sand-deposits in

places is not compatible with such an explanation. In some of the map-descriptions it is stated, with regard to these less well-

developed dunes that humous deposits occur in the dune-sand (sheet Schilde a. o.) This might thus indicate that secondary dune-drift has been at work and that the

present topography of the dunes perhaps is not original.

The dune-field south of Frankfurt a/M is the largest one situated outside the Urstromtdler; and consequently a somewhat detailed description may be allotted to it.

The dunes are here to be found scattered or together in chains on the diluvial

plains extending from Frankfurt southwards on the east side of the Rhine. Be- sides the dunes, there are quite extensive areas which are covered by undoubtedly aeolian sands to a thickness of '/2--1 m, but which are not built up to dunes. As I have myself made only a short visit to this field, the following description and discussion are principally based on the study of the geological maps and the descriptions appended to these.

The material comes undoubtedly from the Rhine excavations in the beds which the river itself and its affluents have deposited during a previous stage. Already the fact that the dunes are all situated on the east side of the river clearly indicates that they are mainly driven by westerly winds. This is also shown by their profile

198 IVAR H O GBOM

grading slowly to the west and more steeply to the east. The dunes are not

very well developed, however, this seemingly being due to irregular winds

during the time of their deposition, and not to later transformations in a half-bound

stage, as they show no signs of destructive forms, such as >Kupsten> or wind- furrows.

In respect of morphology this field does not present much of special interest. The arrangement at some places of the dunes in parallel chains (e. g. Vierheim-sheet), lying farther from each other than what corresponds to the usual distance between dunes, is to be interpreted as due to two different periods of action, perhaps with

only a very short interval. This distribution thus would seem to be a parallel on a very small scale to the distribution of the dunes between the Danube and the Tisza described below. The bow form is not very well developed, the wings usually having the forms of delayed spurs from the main range. The altitude of the dunes is generally only about 6-8 meters, but among the highest ranges some of I3 m in height are met with.

Although not so conspicuous, two dune-ranges also are to be seen on the

Mannheim-Ladenburg sheet, where the easternmost one is a somewhat broader complex of several dunes and thus might be characterized as a little dune-field extending in north-south direction.

The relation between the dunes and the different stages of erosion of some of the Rhine affluents, especially the Neckar, is of importance, as a determination of the relative age between the dunes and the old meanders is possible. On Fig. 28 I reproduce a sketch-map of the Neckar excavations in the dune-bearing plateau, based on geological and topographical data from the Ladenburg sheet.

The dunes occupy here a zone 2 to 3 km broad, the western border of which has an altitude of 102 m, that is to say about io m above the Rhine level. Eastwards the plain slowly rises a couple of meters, the base of the easternmost dunes lying on i05 m altitude.

The plain on which the dunes are situated represents a relic part of the surface of the old Neckar delta; most other parts of it within the area of the map being cut away by the old meanders of the rivers. In most cases, however, these meanders are topographically very insignificant, as shown by the figures on the sketch- map indicating the heights above sea-level.

Examining the geological map, one finds that aeolian sand of a thickness less than I m also covers even other parts of the land than the above mentioned zone. All deposits which can be termed as dunes, however, lie either on the old delta-plain or eastwards from the main dune-bearing zone above Io05 m altitude. Even regarding these latter occurrences it is probable that they rest on remnants of the old delta, although it does not with certainty appear from the geological


map if they have not in some cases wandered out over meanders of the oldest

generation. As regards the very minute layers of aeolian sand, which the map shows also

on the bottom of some meanders of the oldest generation, it is very possible that

143

DI]=

1012 Friudechhfem

Fig. 28. Sketch-map showing the position of the dune-ranges in relation to the old meanders of the Neckar and the Rhine. According to the geological sheet

Ladenburg.

they have been blown out over the water and thus do not prove the existence of later sand-drift.

Anyhow, it is striking, that, with the possible exception of some of the oldest beds of the Neckar, the dunes are confined to the parts of the delta above the

very shallow meanders. Although later aeolian transport of the dune-sand thus

200 IVAR HO GBOM

may have taken place on a small scale, it is evident that there has been a previous sand-drift period with climatic conditions other than those which have since prevailed.

It seems most natural to regard the Rhine-dunes as belonging mainly to the same epoch as the dunes of the Urstromtiler. This interpretation is favoured both by the fact that they were driven by westwinds and by their antiquity, as

proved by their relation to the old beds of the rivers. There are, however, also differences to be noted between the Rhine dunes and

the northern dunes. The former ones do not show the same regular shape, especially as regards the development of the windward- and the lee-sides. That more irregular winds have been active on these dunes is also shown by the

irregular beddings to be seen in some cuttings within them, which where mentioned

already by Thuirach in his description appended to the geological Ladenburg sheet. I have myself had an opportunity to make the same observations at the same place from where he drew a profile for his description and even at other

places, but during the time of my visit no such great cutting was open. The

profile shows beds mainly corresponding to lee-side deposits blown from east and

west, the latter ones being the more important.

North-east from Dresden there is a dune-field extending in WNW-ESE direction with a length of 8 km. The dunes are not very well developed; it is noted in the description appended to the geological maps that it has been impossible exactly to draw them. The aeolian character of the dunes was mentioned as

early as 1864 by v. Gutbier, which is not astonishing, as in many places the sand is still drifting.

The material comes from the horizontally bedded sand-plateau on which they are lying. The dunes are generally io m high and, locally up to 20 m. The windward-side inclines towards the SW and the lee-side towards the NE.

It is recorded that within the dunes old trunks are met with, contrary to what is the case at most other fields. From what is known about this field it thus seems uncertain whether the dunes are to be regarded as ancient in the same

meaning of the word as can be used about the dunes in the Urstromtdler and even about the dunes east of the Rhine. Though it may ultimately prove possible to distinguish older forms amongst the Dresden dunes, the maps and descriptions available do not permit it.

The theory of Solger, already alluded to in another connection, has got very little support amongst those geologists in Germany who have themselves studied the dune problems. In some cases, on the other hand, his views have been

adopted unreservedly by authors of hand-books on geology and studies in


connected branches of science. A closer scrutiny of the theory as a whole thus seems to be in place.

Already when Solger first advanced his hypothesis in 1905, he met with criticism from Lehmann and Wolff, whereas Meinardus from a climatological point of view stated that east-winds must have been predominant during the epoch from which, according to Solger, the dunes date their basal form.1

Solger has later followed up his theory in a series of studies, and his most elabo- rate treatise is to be found in the >)Diinenbuch> (1910o). His last contribution to the question is made in a discourse of 1920.

In the chapter on dune-morphology, I have pointed out the mistakes, which, in my opinion, Solger has made regarding the interpretation of dune-forms. Con-

vincing arguments against the Solger theory, however, are also to be found in some general conclusions involved by it which may be treated in this place. Later on I shall have an opportunity to examine the climatological consequences to which it would lead.

Quite apart from the untenability of the morphological conclusions regarding the orientation of horseshoe-dunes upon which Solger bases his argument, the idea, that the dune-profile everywhere has been overturned, leads to absurd conclusions. The combination of a west-wind profile and an east-wind basal form

according to the interpretation of Solger, does not appear in single dunes or

single dune-fields only, but it is without exception the rule on all ancient inland dune-fields in Germany, Poland, and Scandinavia. If Solger were right, the conclusion must be that dunes once formed are always exposed to winds of opposite direction, just strong enough to reverse wind- and lee-sides, but leaving the basal forms untouched.

From the German dune-fields there is in fact not a single instance known where the winds, which, according to Solger, have turned over all wind-sides and

lee-sides, have been able to produce even the smallest free dune turning the convex side against the wind. Yet more impossible in its consequences is the

Solger hypothesis in regard to the Swedish dunes. On the Mora field the bow- form of the dunes is very well developed, but there is no possibility of conceiving any winds blowing from the SE in which direction the convex fronts of the dunes face. The same is to be said about the other dune-fields of Scandinavia without

exception. This fact seems to me to offer one of the most objective and decisive arguments against the Solger hypothesis and in favour of the opinion regarding the different dune-forms which I have advocated in this treatise, and also in favour of the interpretation of the German inland-dunes as being built up at a later epoch than what corresponds to a periglacial formation.

1 Verh. des 15. deutsch. Geographentages zu Danzig, p. XXXII. Berlin 1905.

202 IVAR HO0GBOM

The preceding description of the German dunes, as well as the critical remarks on the Solger theory, implies an indirect determination of their age, in so far, namely, that they can have had nothing to do with the north or north-east winds which must have prevailed outside the border of the retreating land-ice. Accord-

ingly, the dunes, in their present form, must be of younger date. On the other hand, while it seems impossible to fix their age more precisely on the strength of the purely geological data hitherto known, it is evident that they are not of recent origin, but that they bear witness to an epoch, the climatic conditions of which differed from those of today.

In this case, however, archaeology seems destined to solve the problem, thus

repaying a service of the same kind wich geology has often rendered that science.

It is obvious that if archaeological finds belonging to a certain age are made on the slopes of the dunes, only very insignificant sand-drift can have taken

place afterwards. By the accumulation of sand an object may be embedded within a dune; the final position must be that it rests on the bottom plain either below or between the dunes. Unfortunately the exact statements as to position of the archaeological finds made in dune-regions are few; mostly very vague information only is given, so that detailed conclusions cannot be drawn.

Attention was first drawn to the importance of archaeological finds for the determination of the age of the dunes by Wolff in the discussion after the Solger theory had first been advanced (1905).

From the finds of neolithic tools on dunes in the Vistula delta he concludes that the dunes date from an early period, probably from the litorina time.

Since then Solger (i9io) and Keilhack (1917) have mentioned the neolithic finds as verifying the age of the dunes, but without giving further particulars. Wahle (1918) on the other hand, who accepts the theory of Solger, dwells more

fully on the circumstances under which the finds appear, and in the list which

accompanies his work it is possible to examine in each case what is known about the positions of the finds. Mostly it is noted that the finds in question are made in bare dune-sand (>>frei gewehter Sand> etc.) but there are also cases in which finds are met with on, or immediately below, the surface of overgrown dunes. That these are less numerous may partly be due to the less recognizable character of the forest-covered dune, the true nature of which may have been overlooked by the observer. Anyhow, a sufficient number of neolithic finds have been made to prove that dunes already existed in the corresponding period and that no general sand-drift has taken place afterwards.

It is true that there is little known about finds from the interior of the greater dune-fields, but negative conclusions as to the age of the dunes must not therefore be drawn, as these regions could not have offered very favourable conditions


for settlement and, besides, the chances of making finds in the forest covered areas are comparatively small.

The possibility is left, however, that the finds have been made on dunes which have remained, while other dunes from the same time have been destroyed by later sand-drift. A reference to the sketch-map from Luibben showing two phases of dune-drift might be in place in this connection. If further archaeological or

geological investigations should prove that there has really been a later and less extensive sand-drift on the old dune-fields, it seems probable that the dunes on which finds hitherto have been made correspond to those the remains of which are to be seen in the complexes of the Lubben type.

To conclude, the archaeological finds prove that the great dune-drift took place before the end of neolithic time, and that, if there has been a later sand-drift

period, this has been less extensive. Further, the archaeological finds do not contradict that interpretation of the two phases of dune-drift met with at some

places (e. g. Liibben) which morphologically seems to be most probable, namely, that the first phase without interruption has been followed by the second phase.

Dunes in Poland and the Baltic States.

The dune-fields situated within those parts of present-day Poland which for-

merly belonged to Germany, are known from the descriptions of German scientists, while until lately only scanty and incomplete notices had been published from the formerly Russian parts of that country.1 This deficiency has in great part been supplied by the investigations of Wunderlich (1916) and Lencewicz

(1922). The fact that the Polish geologists formerly only more cursorily have touched upon the dune-problem is due, according to Lencewicz, to the inaccessi-

bility to the scientists of the topographical maps during Russian r6gime.2 Lencewicz publishes in his treatise a sketch-map of the distribution of the

dunes within Poland, which map has served me as a basis for my map Fig. i8 in what regards what was formerly Russian Poland. How far the map of Lence- wicz can be compared with that of Keilhack in exactitude I have not been able to controle. Thus it is possible that on the map compiled by me the Polish

part is not quite commensurable with the German one. It is clearly to be seen, however, on the map that the dune-formation extends

over wide areas in Poland, and further that dunes are not so exclusively con-

' Unfortunately language difficulties have prevented me from making use of works on dunes written in Russian or Polish.

' A similar drawback has made it impossible for me to enter upon the morphological details regarding the dunes east of the frontier of the German Empire, as the only maps which have been accessible to me are the maps in I : I36,ooo of the Russian General Staff and in I : 200,oo000 of the K. K. Militlir-

geographisches Inst. in Wien.

204 IVAR H10 GGBOM

nected with the border drainage channels as in Germany, although a tendency in that direction may be noticed. This difference in the geographical distribution of the dunes in Poland and Germany is also pointed out in the treatise of Lencewicz.

Wunderlich, as well as Lencewicz, recognizes that the dunes have been driven

by west-winds. The former bases his conclusions in that respect chiefly on the

jk

S#r6c

(p Ajo wswaL A -.PAY* uwyuw6r al Ark- RMZWIN ;

4t:

-Aso

e

20 km r... kf"6w

AL6

Fig. 29. Dunes in the neighbourhood of Warsaw. After Lencewicz (1922, p. 23).

geographical distribution on the dunes. He has found that where the rivers run in a south-north direction the western shores are practically free from dunes, whilst these abound on the east-sides. This he states to be the fact especially regarding the Vistula, the Prosna, and the Warta (Warthe). The same rule he finds verified on the rivers Narew and Bug, the former running NE-SW, the latter ENE-WSW. Lencewicz, on the other hand, contests this statement, re-

ferring to his map showing the distribution of the dunes. Even this map, however, seems rather to support the opinion of Wunderlich, at least concerning the north and west of Poland.

Lencewicz also opposes, however, the hypothesis of Solger on the barchan- nature of the horseshoe-dunes as on the whole the theory of the periglacial genesis of the inland-dunes maintained by the lastmentioned author, Tutkowsky, and others, but he bases his conclusions upon the morphological evidences of the


dunes themselves. In fact he presents a very clear and decisive criticism of the fundamental errors regarding dune-morphology, which have led Solger and others to confuse transversal dunes and barchans.

The morphology and the position of the dunes in the border drainage channels of Western Poland is much the same as that which characterizes the German

Oe e e *e

e e

e e *0Iwe

e a el .e4, e; O e

to to /e e to

/

to 0 Ae#1e.o il t

Fig. 30. Part of the dune-field of Puszcza Kampinoska NW of Warsaw. Scale I :40.000. From the topogr. map of the Russian General Staff after Lencewicz (1922, p. 25).

dunes and which has been described above. Especially there is in all essential

respects a very great similarity between the Warthe-Netze field and the dune-fields on the left side of the Vistula south of the towns of Thorn and Bromberg. Here also very beautiful instances of deflation areas to the west of the main dune-fields

occur, often partly enclosed within the outmost marginal dunes or dune-complexes. A nearer description of these fields would, therefore, mainly be a recapitulation of the descriptions already given.

Also the dune-field of the Puszcza Kampinoska to the north-west of Warsaw is of the type mentioned (cfr Fig. 29). I reproduce in Fig. 3o after Lencewicz a

part of the map of the Russian Gen. Staff from this field, which on account of its accentuated drawing gives an unusually good idea of the topography within such a network of dunes.

206 IVAR HO0GBOM

As regards the morphology of the dunes on the east-sides of rivers running in a south-north direction, the observations of Wunderlich are very instructive. He points out that the youngest dunes nearest to the river-sides constitute ridges practically parallel to the river, whilst those situated farther east are characterized

by a parabolic form which is more pronounced the farther the dune has wandered. He recognizes that the direction of the former is influenced by the direction of the river, while the latter better indicate the direction of the dune-driving winds, which he finds have been between W and NW. The figures given by him for the length of the parabola-axis, up to 2,5 km and more, are fairly accordant with those of some German fields. Wunderlich also states that a profile observed

by him in a fresh cutting in a dune east of the Warta shows typical west-wind stratification. All the facts taken together contradict the east-wind hypothesis of

Solger.

Lencewicz states that some of the Polish dunes are always in a wandering state, and therefore he concludes that no special hypotheses as to earlier dry periods are necessary to explain their development. He seems also inclined to bring these observations to bear upon the interpretation not only of the Polish dunes, but also of the German ones, and it seems as if he would ascribe the different views of Solger and others to their overlooking a phenomenon generally met with in the dune-regions. Thus he says (p. 53): )D'apres Solger le sable 6olien ne se forme plus, actuellement il ne fait que se deplacer. Toutkowskij dit, qu'il ne connait pas un seul exemple de la formation d'une nouvelle dune>. Unfor-

funately, the notices of Lencewicz regarding recent sand-drift are very scanty; and a more detailed and exhaustive investigation of the conditions under which it takes place, and the forms destroyed and built up, would be of great interest from many points of view for the understanding of the old dunes. Anyhow, there is no doubt that at several places in Poland sand-drift is going on on a greater scale than would have been supposed from earlier descriptions. Nevertheless Lencewicz has overlooked some important facts which prevents too far-reaching conclusions as to actualistic views on the genesis of most of the inland dunes. This is evident even if the negative formulation of Lencewicz is taken into account: >)Il est bien possible que jadis nous avons eu des conditions meilleurs pour le

developpement des dunes, mais l'observation montre que la d6flation peut se pro- duire dans notre climat>.

In the first place, it is naturally inaccurate without reservations to apply to the German dunes the conclusions based upon studies in Poland, where the climatic conditions are of far more continental character, particularly as the observations of the German scientists are incompatible with his own. In the final

chapter I shall have an opportunity once more to return to the theoretical im-


portance of the different climatic conditions of the zones, within which the inland dunes of Central Europe are situated.

But even regarding the Polish dunes it seems to be not only possible but certain that more favourable climatic conditions for dune-formation have been prevalent during past epochs. The existence of marshy ground over which the dunes have wandered may be noticed even in the map here reproduced. This fact indicates that the dunes in question may have been driven at a time when the climate was less humid than is the case to-day, for no elevation of the level of the Vistula, similar to that of the Warthe and the Netze, seems to have taken

place. In Poland, as well as in Germany, the present summer winds as to their di-

rection accord fairly well with those which the dunes bear evidence of. Thus Lencewicz publishes a table (1922, p. 42) of the distribution of the winds at Warsaw during the different months of the year which shows the predominance of westerly and (for July) north-westerly winds during the summer. He adds, however, that even the influence of the north-winds, which are most frequent only in May, can be traced on some dunes the branches of which are unsymmetri- cally developed. This seems rather astonishing as according to Lencewicz' table winds with a southerly component (SW-S-SE) constitute 38 % whilst those with a northerly component (NW-N-NE) constitute only 30 % of the winds of the

year. In discussing the time of a supposed intenser dune-drift than at present, Len-

cewicz concludes that this must rather have been the Litorina than the An-

cylus epoch He bases this opinion on a study of the situation of the dunes rela-

tively to the terraces of the Vistula. He admits, however, that the determination of the respective ages of the latter is rather uncertain. It is remarkable that dunes occur on comparatively low terraces, and from this fact Lencewicz natu-

rally draws the conclusion that the dune-drift has continued until a relatively late

epoch. A quantitative study of the dune-drift on the lower and on the higher terraces is desirable, however, before any safe conclusions can be arrived at re-

garding this question. To judge from the instances cited by Lencewicz, it seems most probable that the dune-drift on the lower terraces only corresponds to the modest dune-drift of to-day, and that it means only that there has been no definite end of the dune-drift period in Poland, but that during later times it has been confined to particularly exposed places.

On the strength of comparisons with other inland dunes I should regard also those in Poland as mainly having been driven during an earlier epoch than is

supposed by Lencewicz. And according to the above, none of the facts given by Lencewicz seem to contradict this opinion.

208 IVAR HO0GBOM

The dunes within the southernmost part of Poland (the former Austrian Galicia) have been studied by Romer (1907). Although in many respects his opinions differ from those of Solger regarding the interpretation of dune-forms, yet he believes in east-winds as having been of influence for the dune-formation, which is also regarded by him as periglacial. Besides, he strongly emphasizes the fact that most of the dunes have to be considered as shore dunes, the directions of which are due to the directions of the rivers in question and to those subordinate winds which blow at more or less right angles against the shores. In this latter

respect he goes perhaps too far, as even winds blowing rather obliquely against the shores produce the same effect; and thus probably also in these regions the

prevailing winds in most cases suffice to explain the development of dunes. There seem to be instances, however, where shore-dunes are met with on the wrong side of the river, but in such cases the more unsheltered position with regard to winds coming from the river-side have certainly caused the seemingly reverse sand-drift.

In describing the dunes of Baruth, I mentioned that traces of older surfaces such as that illustrated in Fig. 23 are only exceptionally to be found in the cuttings in Central Germany. That instance is, in fact, the only one I have met with there. Further to the east, on the other hand, secondarily overblown dunes are, according to different authors, very common. The observations of that kind made

by Korn at Czarnikau have already been mentioned.

According to the recently published notes of Krukowski (1922), the phenomenon seems to be still more conspicuous in Poland. He summarizes the conclusions arrived at as follows:

>)La stratigraphie petrographique des dunes du bas-pays de la Pologne, en

partant des couches superieures est la suivante: I. Sable eolien superieur; II. Humus fossile; III. Sable dolien infdrieur, constituant la plus grande partie des materiaux, qui composent les dunes. Ces trois formations se distinguent entre elles par leur couleur, leur composition et leur consistance. La formation III a commence a apparaitre au ddbut de la recession du glacier L4. Le processus de son d6veloppement occupe tout au moins la plus grande partie de l'ensemnble de l'piglacial et se termine dans la pdriode s&che de l'Ancylus. I1 constitue donc la premiere 6tape de formation des dunes. La formation II correspond surtout a la Littorina et au premier grand arret de d6veloppement des dunes. La formation I correspond a la periode seche terminale de la Littorina et a la periode seche de la Mya. Les humus peu d6velopp6s des forets conif~res qui recouvrent la formation I sont de date plus recente.

>)Dans la formation III on trouve des documents archeologiques se rapportant aux industries magdalinienne moyenne (ou inferieure), swid&rienne, azilienne et


tardenoisiennes infirieure et moyenne. Les industries naolithiques sont lies t la formation II. Enfin l'6ndolithique, les documents protohistoriques et historiques appartiennent 't la formation I. Toutes ces industries ne se rencontrent pas si- multanement sur une meme coupe.

>Mais chacune d'elles se retrouvera le plus souvent, dans la formation qui lui

correspond au point de vue chronologique. Jusqu'at pr6sent on n'a retrouv6 les

plus anciennes (les v6ritables magdaleniennes notamment), que dans les zones les

plus meridionales. Cela nous permet de croire que notre idee peut pr6senter utine certaine valeur non seulement au point de vue m6thodologique.>

The special work on these questions which Krukowski says he is going to

publish, will certainly reveal facts of interest for a surer judgment of the outlines

quoted above. His statement that the later sand-drift only to a small extent has influenced the primary shape of the dunes contradicts the opinion of Lencewicz about the importance of recent dune-drift. On the other hand, Krukowski's mention of the (humus-free) older dune-sand as bearer of pre-neolithic finds is

surprising. One should have expected such finds on the ground over which the dunes have been wandering but hardly in the dune-sand. Probably a further

investigation will give more convincing results as to the stratigraphy of the archae-

ological finds. At present it seems hardly to be believed that the different archaeolo-

gical epochs would be so regularly registered by the dunes as Krukowsky thinks. From the Styr-region Romer (1907) reports that a culture-layer is often met with,

situated some decimeters below the present surface of the dunes. He adds, that

although closer investigations have not been made regarding the finds, these seem to be neolithic. The find-places seem to indicate that, even before the neolithic settlement, the old dunes had been partly denuded during a period of humid climate. Interesting also is the statement that the settlements are situated on the crests of the dunes, that is at places which even nowadays would be most habi- table, as the intervening ground is marshy.

The explanation advanced by Korn regarding the elevation of the level of the

ground-water in the Netze-field can naturally not be applied to these regions. It thus seems that the marshy ground between the dunes really must indicate a change in climate from a dryer to a more humid one.

From the former Baltic provinces of Russia Hausen (1 913, a) gives some mi- scellaneous statements about the occurrence of inland dunes. Unfortunately his notices are very scanty and not accompanied by maps, so it is difficult to form a conception of the morphology, and above all of the regional distribution, of these dunes. Summing up the observations made, Hausen states only (1913, b, p. S141): _>Fossile Diinen kommen im Binnenlande oft vor? and >Ich selbst habe fiber diese Bildungen keine besondere Beobachtungen angestellt.>


210 IVAR HOGBOM

The maps of the Russian General Staff from these parts on a scale of I:I 26,000 are not sufficiently detailed for the dunes generally to appear, and when in one or two cases they do, the different inclination of wind- and lee-side does not

appear. I have not had access to maps on a larger scale, if there are any such for these districts.

From the low moor-land east of Riga Hausen states (1913, a, p. 125) that the

railway crosses old dunes, which generally have a N-S length-direction and a

height of up to io m. Likewise, there are dunes between Riga and Kurtenhof, and evidently in several places within the lowland of Mitau. None of these occurrences appear as continuous dune-regions on the map, though in some places the topographical inclination signs possibly refer to dune-sides. No conclusions can be drawn, however, as to the distribution or the general direction of the dunes.

One of the best developed of the dune-fields seems to be that between Wolmar and Walk (Walga). Hausen states (1913, a, p. 103), about this field, that the dunes are of a lenghthened shape like oses, but says nothing of their dimensions or orientation. From one place, however, he notes that the dunes rise out of

marshy ground. Thus, from these regions also there are indications that other climatic conditions have been prevalent during the epoch of dune-formation. On the map of the General Staff some dune-like ridges are certainly indicated, but it would seem that only those bordering on the road have come in and that more distant formations of this kind have not been reconnoitred. It is not possible, therefore, to draw any conclusions from the maps as to the wind-direction or to the distribution of the dunes.

North of Lake Peipus there is a continuous dune-field which appears on the

map (Gouv. Kurland IV: 6). It is made up of a swarm of dunes, about twenty in all, the length-direction of which lies NE-SW, and which generally show a

gentle curving, concave towards the NW. The topographical notation indicates no difference between wind-side and lee-side; but with regard taken to the basal form there can hardly be any doubt that they are really dunes of the usual type.

Of this field Hausen says (1913, a, p. 62): >>So trifft man im N des Peipus eine grosse Schar ungef'ihr NE-SW streichender, kleiner, auf der Karte wurm-

f6rmig aussehender Diinenwalle, die oft vom Moorboden umgeben sind. Sie markieren offenbar succesive Lagen eines Strandes, der sich gegen SE zuruick-

gezogen hat. Diese Strandverschiebung kann jedoch nicht als Resultat einer

Landhebung angesehen werden, weil die Gegend fiber der marinen Grenze liegt. Meiner Auffassung nach sind diese Wille als Eisseestrandbildungen zu deuten."

Though on the topographical map there are no figures showing the altitude at the dune-field, it is clear from the situation and shape of the dunes that this formation has not been caused by any successive retiring of the shore-line. Under


such circumstances it seems to me to be the most natural to interpret these formations as normal inland dunes, which have been formed independently of any displacement of the shore-line. If a displacement towards the SE had taken place, as Hausen supposes, the dunes would not have shown a concavity towards the NW. The material of the dunes is derived from the sediments of the ice-dammed lake which, according to the researches of Hausen, once covered Peipus and the surrounding country.

Thus, there is every reason to regard the dunes north of Peipus as equal to the other continental dunes, though they have been driven by more north-westerly winds than has been the case within the German and Polish dune-fields. This is also in good accordance with the opinion of the general pressure distribution at the dune-drift time set forth in the following chapter.

The Hungarian Dune-fields.

My intention, when I commenced my studies of ancient dunes, was to confine them only to the fields situated within the geographical unity formed, from a

quaternary point of view, by the once ice-covered parts of Northern Europe. I went also to Hungary, however, mainly in order to acquaint myself with dune-

morphology. From the descriptions of Cholnoky one could judge that the fields there would offer better possibilities in that respect than any other fields in Europe, and, besides, Cholnokys investigations had made Hungary a classic ground for dune-studies. Already in the introductory chapter on dune-morphology I have had an opportunity to mention some dune-types, characteristic of the Hungarian fields and first described and named by Cholnoky, namely the wind-furrows and the garmadas. In the following pages I shall also give some further illustrations of these forms.

Having seen the Hungarian dunes, however, I found that, even from another

point of view than that of morphological comparisons, they have to be treated in connection with the northern ones. For although the bulk of the Hungarian dunes are of quite another age and shape, at least at one of the fields there seem to exist even older forms which must probably be paralleled to the northern dunes.

On the great Hungarian lowland, the Alfdld', now by the Peace partitioned between Hungary, Roumania, and Yougoslavia, one finds in fact some of the

greatest inland dune-regions of Europe. And as most of them still lie within the

1 Alf61d, in Hungarian meaning lowland, should as geographical nomen proprium be used to signify the great lowland mainly extending east of the Danube as distinct from the Little-Alf61d, the lowland on both sides of The Danube in the region of Posony (Pressburg, Bratislava). Cfr Cholnoky (19to a, P. 275).

212 IVAR HO GBOM

borders of present-day Hungary, they may easily be visited by interested students.

The following pages are based on observations of my own during a short stay in the country and on studies of the topographical maps, so far as the conclusions do not coincide with the theories of Cholnoky related below.

Cholnoky has on several occasions discussed the Hungarian dunes. On account

: , . . .. . . . . . . . , - .- , " . . . - .

0 100 km.

2 ~3 4

of the small scale of my sketch-map Fig.31, I have had to refrain from using the detailed map of Chol-

noky (g19io) as basis, but confined myself there to demonstrate onlythe situation of the great dune-

bearing areas according to the recent map of the geology of Hungary by L6czy (new edition 1922).

Regionally, and also from a genetic point of

view, the dunes of the Alfold group as follows:

The Nyirsg field in the north-eastern part of the

Alf6ld, The fields between the

Danube and the Tisza, and The Delibldt field, in the

southeastern corner of the

Alf6ld, now wholly within the borders ofYougoslavia.

Even outside these fields, which have a real

inland-character, dunes occur abundantly within some of the meander-re-

gions, particularly on the east-sides of the Danube and the Tisza (cfr Chol-

noky, 1907).

Fig. 31. Sketch-map showing the position of the dune-bearing areas in Hungary. i. Higher areas outside the Alf6id. 2. Dune-bearing

fields. 3. Mainly loess. 4. Mainly alluvial surfaces.


Of the fields mentioned, that at Nyirsig, presents special interest for this treatise, as dune-forms are there met with which are similar in shape, and probably in

age, to those previously described.

The Nyirsig field, in contrast to the fields between the Danube and the Tisza, may be regarded almost as a single complex of dunes which practically may be enclosed within one single boundary line. It is situated on a loess-plateau around the northern part of which the Tisza bends. The altitude of the plateau is about

120-130 m above sea-level, while the plain to the west lies below ioo m. Along the northern parts the dune-bearing plateau is almost bordered by the Tisza, whilst, to the west, there is a broad zone of the young-diluvial plain between the river and the plateau.

Cholnoky regards the shape of the Nyirsig dunes as due to the prevailing foehn-like north-winds (1910 a, p. 291). In accordance to this view he concludes that the fans of the rivers Ondova, Tapoly, Ung, and Latorcza situated to the north of the field have provided the sand-masses of the dunes.

Having had the opportunity of visiting this field and of comparing the dune- forms with those met with in Germany and Sweden, however, I must in some essential respects dissent from the opinion of Cholnoky. As I have previously pointed out, like Cholnoky I consider the longitudinal forms as characteristic of deflation regions or of regions where the wind locally attacks sand-masses half- fixed by vegetation. Cholnoky's interpretation of the dune-forms in Nyirseg, however, does not seem to be fully in accordance with this principle.

The fact is, that in Nyirseg, particularly in the south-eastern part of the field, the dunes have far more similarity to the transversal dunes of Northern Europe than to any longitudinal forms hitherto known (cfr Figg. 32, 33). Cholnoky does not except these dunes, but regards them, as well as the rest, as having been driven by north-winds and only slightly altered by the less frequent west-winds. vDie Kamme dringt der Westwind in ihrem Mittelstiick etwas ostwarts ab, doch bleibt die Hauptrichtung beinahe genau nordsiidlich. Am besten ist die vorherrschende

Wirkung des Nordwindes bei Mairia-P6cs und Hajdu-Saimson zu sehen, doch springt hier auch zugleich die Kombination dieser Wirkung mit der des Westwindes scharf in die Augen> (Cholnoky, 191o a, p. 291). This difference of opinion, whether one regards the dunes as longitudinal forms created by north-winds and slightly altered by west-winds, or - as I do - as transversal forms driven by westerly winds, possibly somewhat modified by north-winds, may seem to be of small im-

portance, were it not that, in the latter case, the dunes must be regarded as

giving evidence of a change in the climatic conditions. I will, therefore, try to further precisize my opinion.

There is in fact a striking difference between the morphology of the central

214 IVAR HO0GBOM

and northern parts of the dune-region on the one hand, and that of the eastern and south-eastern parts of it on the other. First, it is remarkable how much

greater and how much better developed the dunes are in the last-mentioned region.

PooP

-)r

ihdL'/Lva Fig. 32. Part of the south-eastern dune-area of Nyirsdg. Drawn according to the map of the

K. u. K. Militiirgeogr. Inst., sheet Nyir-B61tek and Hajdti-V'mos-Pdrcs.

In the interior of the field the topographical delineation in the maps reminds one

very much of that in the maps from the dune-fields between the Danube and the Tisza, to be described later on, although in Nyirseg the striking is N--S instead of NW-SE.

The dunes in the south-eastern parts of the Nyirs6g field, part of which is re-

presented by Figg. 32 and 33 are both in size and shape almost identical with the


transversal dunes of some fields of Northern Europe. Interpreted as transversal dunes, they indicate that the sand-driving winds have been blowing from the WNW. Already on the topographical maps (1 :75,00ooo) the difference between wind-side and lee-side is visible on most of the dunes, and the slight bow-form with the concave sides towards the WNW is quite general.

The bow-formed dunes lie outside the great sand-masses of the inner parts of

9:1 . -J

4r-., . - M 4 , ?

We 104 rl =13 4

1,w ti- - fAS

Fig. 33. Dune-morphology of the south-eastern part of the Nyirseg field, scale I : 75.000. From the

map of the K. u. K. Militiirgeogr. Inst., sheet Nagy-Kill6 and Nyir-Bitor.

the field and have wandered out over plain ground. They are thus to be regarded as inflation dunes Even this fact supports the interpretation of them as transversal dunes driven by westerly winds and not as longitudinal ones, as the latter forms are characteristic of deflation regions.

Other circumstances also indicate that these dunes represent ancient forms, which have developed when the predominant winds were other than the present northern ones. Where wind-furrows are to be seen, they correspond to the present north-winds, while there are no wind-furrows called forth by west-winds, although the dune-ridges directed north-south would present far more prominent obstacles

216 IVAR HOGBOM

to be cut through by these winds. Thus it would seem that west-winds do not

nowadays influence the dune-topography; this, however, the north-winds do, especially in the interior of the field, where in fact beautiful wind-furrows and garmadas are always developing at places where the vegetation in some way or other has lost its binding power.

There are also other objections to be raised against the opinion of Cholnoky, that the bow-formed dunes are the products of alternating stronger north-winds and less strong west-winds. The obstacles presented by the dune-flanks to the

prevailing north-winds, would in the first place be attacked by these and obliterated.

Besides, if one wind produces longitudinal forms, there is every reason to suppose that another wind, blowing from another direction and working in the same ma-

terial, would also work out longitudinal forms.

Thus, all facts taken together seem, in my opinion, to indicate that the dunes in question are of transversal type, and that they have been driven by WNW- winds; this does not correspond to the present climatic conditions, when, as

Cholnoky points out, the prevailing winds come from the north. Another fact which goes to prove that these dunes date from older times, the

climatic conditions of which were other than the present ones, is the existence of

marshy ground and small pools between many of the dunes. This is especially the case in the very part of the field drawn on the sketch-map Fig. 32. On account of the small scale, however, it has not been possible to distinguish these occurrences.

A glance at a map shows that the distance between the southernmost dunes in Poland and the Nyirsig field is not very great, in fact only some 2oo00 km. It is true that this interspace is occupied by the geographical barrier of the

Carpathians, on both sides of which different climatic types might be expected. The climatic influence of the Carpathians, however, should not be overrated, especially when discussing a period during which an arid climate, distinguished by west-winds, dominated the north-side.

Although many questions remain to be answered before a definite conclusion can be drawn, it seems thus most probable that the older transversal dune-forms at Nyirsdg are of the same average age as the northern dunes. The great west- wind sweep of finiglacial time is thus probably to be traced as far south as to the north-eastern parts of the Hungarian lowland.

The fields between the Danube and the Tisza. As shown by the map of Cholnoky (191o a) of the morphology of the Alfold, swarms of dunes are scattered over the northern and middle parts of the old-diluvian land-surface between the two rivers

falling within the Komitat Pest and the northern part of the Komitat BTics-Bodrog. According to Cholnoky, the dune-swarms show a zonal distribution parallel to


the rivers, indicating three drier periods (1910 b). The dunes corresponding to the first of them have wandered as far as to the Tisza, which in one instance north of the K6r6s junction, because of later displacement of the river-bed, has even cut off part of the dunes which thus now lie east of the Tisza. The dunes

corresponding to the second phase are situated along the middle of the plateau (Kecskem& e- Szabadka), whilst the youngest dunes border the western side of the plateau. A difference in the sand may be observed; the finest, most even-

grained and rounded material is to be found farthest to the east, whilst the sand of the western dunes is more rugged and unsorted (Cholnoky 19io a, p. 292).

The basal forms of these aggregations of dunes of themselves indicate that

they have been driven by north-west winds. Originating from the Danube line, the sand-mass has not been sufficient to cover the whole surface but only spots of it. The fields are thus undoubtedly accumulative, in spite of the longitudinal forms which they usually exhibit. These forms seem, however, to be due to

secondary deflation. The fields are in fact very instructive, although most probably an observer without previous knowledge of yet more marked forms of wind-furrows and garmadas would overlook the true character of the dunes, had not the excellent studies and comparisons of Cholnoky made it clear.

The extensions of the longitudinal dune-forms correspond entirely to the NW- winds which now are predominant in these regions; and although here too it seems

possible to distinguish older dune-forms, they do not indicate any marked change in the wind-direction.

These relic dunes met with at some places are barchans, more or less destroyed by the later sand-drift, which has developed the longitudinal wind-furrows and

garmadas. Only in the immediate neighbourhood of old river-beds there are some

dune-ridges of transversal shape. The development of the longitudinal forms is

mostly complete, however; and there are generally no evidences at all left of any barchans or transversal dunes of older date.

On Fig. 34 I have reproduced a sketch-map of one of the remaining barchans west of the Kolom Lake, near Isztk (Komitat Pest), which is only in the beginning stage of destruction. This dune-hill is partly fixed with vegetation, and

has, therefore, preserved its barchan character as a whole. In many places, however, the sand is quite bare, showing beautiful ripple-marks and edges between wind-side and lee-side; here the characteristic wind-furrow and garmada forms are in the beginning of development. To the east of the highest point, there is

already a distinct wind-furrow with a garmada altering the shape of the eastern

wing of the barchan. The top itself is partly fixed, but another wind-furrow is in the beginning of breaking through there also. Yet further to the west, there is a third wind-furrow. The two last-mentioned ones are without a garmada terminating them; this is in fact a quite usual form.

218 IVAR HOGBOM

In other places in the neighbourhood there are wind-furrows with small deflation witnesses on the sides. Sometimes the side-ridges are clearly recognizable as residua, but in other cases the right interpretation of similar longitudinal >)dunes>> may be overlooked by the unprepared observer.

When I visited this region, strong southerly winds had prevailed for a short time, and there were several opportunities of studying the overthrowing of the

0 .

L

/1

.... i

Fig. 34. Barchan showing later wind-furrows

(marked by arrows). The flank to the right is

being transformed into a garmada. About 5 m. aequidistance between the isohypses Near Iszaik,

Kom. Pest. Eye sketch.

small forms, the great ones everywhere keeping their original shape built up by north-west winds. Besides reversed wind- sides and lee-sides on the smaller dune-heaps there could e. g. be noticed also the rede-

position of sand from a garmada as a little transversal dune with well developed wind- and lee-side in the bottom of a wind- furrow.

South of Budapest in the neighbourhood of the village Dunaharasti, I was fortunate enough to have the dune-mor-

phology demonstrated under the kind gui- dance of Prof. Cholnoky himself. The relief of the land-surface is not so pronounced here as in the easterly fields, perhaps partly because of an older cultivation of the

ground, but anyhow, no one who has studied the Cholnoky treatise on the syste- matics of dunes, can be in doubt regarding the system of wind-furrows and garmadas caused by the here prevailing north-west- winds, which have given the landscape its

undulating character. The region is also interesting, because the longitudinal forms are found near to the lee-sides of transversal shore-dunes, thus illustrating how easily longitudinal forms under special conditions can develop from transversal dunes.

The Delibldt field shows the most impressive examples of longitudinal aeolian denudation and longitudinal dunes. I have not myself had the opportunity of visiting this field, but the oral informations kindly given to me by Prof. Cholnoky, as well as a study of the topographical maps, have enabled me to form a conception of the origin and the morphology of the dunes. Unfortunately, the special treatise on this field prepared by Cholnoky has not as yet been published;


in connection with other problems of the Alf61d, however, he has made clear his

opinion regarding the main features of the morphology.

The Deliblht field is situated on the great fan of waste which has been deposited in the south-eastern corner of the Alf6ld, before the present drainage system of the lowland had developed. In some respects the material of the field, in which the aeolian forces have worked, gives the key to the development of the forms of the dunes. The Deliblit sand is, as Cholnoky points out, no ordinary dune-sand, but has more the character of a dusty earth. This indicates that, as a whole, the Deliblit field, not only the south-eastern beginning of it, is a deflation region, where only an insignificant separation of the material as to its coarseness, has taken place. The ridges are thus to be regarded rather as deflation remnants than as dune-forms in the strictest interpretation of the word. Under such circumstances it is quite natural, that longitudinal forms should prevail, and, in fact, no other field offers better examples of a regular rifling. It is necessary, however, to state that the longitudinal ridges, as a rule, are not to be regarded as untouched remnants of the original deposits; but the decisive process seems to have been the excavation by deflation, and the local accumulations have

adapted the longitudinal depositions accordingly. The longitudinal forms, being less exposed to the action of the wind, explain also why the sand, under the influence of the dry and strong south-easterly Kossava-foehn, has not been blown free from the dusty material. It would be very interesting to know, whether there is not to be found a material with a coarser medium size in the central and distal parts of the field. If, contrary to the conditions in normal fields, this should be the case, it would be possible to prove where the deflation ends and where accumulation predominates. The fact that some barchans are to be found in the centre of the field seems also to be in accordance with this supposition. That they are lacking within the distal parts of the field may be due to a rapidly decreasing power of the wind as it passes over the field, in consequence of which

only the finer material is transported further. If this is the case, the maximum coarseness of the grains would be found in the middle of the field. Anyhow, interesting data must be found if an investigation of the sand should be carried out along a south-eastern - north-western line of this dune-field.

The usual rule, that negative conclusions as to previous climatic conditions are not to be drawn, because remains of ancient dune-forms are lacking, is not quite in place at Deliblit. There the question arises how it is possible that no separation of finer material has occurred in previous epochs, whereas present dune-drift is going on, or was going on before the artificial binding of the sand begun.

The question cannot perhaps be answered until our knowledge of all the factors concerned has been widened; but the possible interference between the local

220 I V A R H O GB O M

winds and the more general west-wind system may offer one explanation, which

has, however, to be further proved. I have thought the Deliblkit field worth mentioning, though it does not show

distinct ancient forms. It is, however, one of the largest of the recent inland dune- fields and illustrates the conditions which make dune-drift possible during the present climatic epoch, that is to say, in this place the sand-deposits cut through by the Danube and the strong wind sweeping down from the mountains. It is true that sand-drift also takes place in other regions of Hungary; but there it is a question of rearranging the old dunes built up of the sterile free-blown sand, whilst, at Deliblkit, the ground in itself offers a fairly good soil for vegetation, as is indeed proved by the cultivation, which Hungary had just completed to a

high degree of efficiency before she lost this ground.

CHAPTER IV.

Some climatological Conclusions.,

Few, if any, problems have roused such an animated discussion amongst Scan- dinavian geologists as that concerning the late quaternary development of the climate, and it is natural that this should be so. Hardly any other chapter of

geology embraces such a multiplex material requiring to be managed with a de- tective's skill in combinations and sense of the distinction between the essential and the accidental. Especially this is true about the biological and phyto-geographical investigations, which, no doubt, have to solve most of the climatological problems of postglacial time.

I In order to avoid any extensive terminological definitions and to facilitate an outlook for foreign readers over the problems here to be mentioned, I publish below an abbreviated synoptical table on the principal divisions of late glacial and postglacial time according to the nomenclature in use by Swe- dish scientists. Broader summaries of these problems can be found e. g. in L. v. Post (1909, p. 638) and A. G. H6gbom (1913, p. 114). Cfr also Sandegren (1915, p. 37) and Sundelin (1917, p. 89).

Thousands of years: II Io 9 8 7 6 5 4 3 2 I Chr. B. I 2 t I I I I

Geochronology and geolo- Gotiglacial Finigl. P o s t g I a c i a time. gical divisions of De

Geerwtigim. and followers, ti.me time.

History of the Baltic Baltic Ice-Lake and Ancylus Littorina L i m n e a Mya (Munthe). Ice Sea stages. stage. stage. stage. st.

Climatological divisions Arctictim e.[ Sub- Boreal time. Atlantic time Sub-boreal Subatl. and (Sernander a. o.) arct. (Warm, (Warm, time. present time

dry). humid). (Warm, dry). (Cold, humid).

Archaeological epochs Stone Ag e. Bronze Iron Age and (Montelius). Age. histor. time.


Physical geology offers fewer possibilities for climatological investigations, but, on the other hand, the results obtained may be more unquestionable.

The great improvement in climate in the formerly ice-covered North Europe, of which the ice-melting itself gives evidence, is no longer the only testimony of a purely physical kind, which we possess regarding changes in the climate at the end of the Ice Age. The most important of the later detailed investigations, the

geochronological studies of De Geer and his followers, have given quite new clues for the comprehension of the climatic march of events during the melting away of the land-ice from Scandinavia. And certainly, the final publication of the

investigations upon which this chronology is based, will reveal further material also for climatological conclusions regarding the epoch in question.

From the point ofview of the present treatise, the greatest interest is attached to the climatic changes shown by the different phases of velocity in the ice-recession.

Briefly, the results in that respect of the work of De Geer and his collabora- tors are as follows. From the southernmost part of Sweden and to the conspicuous terminal moraine belt at the great lakes, the ice-border regressed with a medium velocity of about ioo m a year along the central and eastern zone of the peninsula but considerably more slowly in the west. After the delay of some centuries at the moraine-belt, the ice began gradually to regress with far greater rapidity, showing annual border displacements up to 200 m in the central re-

gions, and 300 m and more in the eastern regions (De Geer, 1908, p. 461, and

1914, the map showing the aequirecesses). To a certain degree, the great annual regression of the ice-border over the part

of Sweden which at that time was below the sea-level, may have been due to the

cutting off of ice-bergs (>calving>), but its rapid retreat continued also when the ice-border had passed the limits of the highest finiglacial sea. Thus the difference established between the speed of the retreating ice-border in the southern and in the northern parts of the country cannot be explained otherwise than by a considerably higher summer temperature or a smaller snow precipitation or both factors combined during the later phase.

The main features of the climatic epochs during the time of the melting away of the land-ice from Scandinavia are also well established by the successive immi-

gration of plants. In South Sweden the receding ice was followed by an Arctic

Regarding the above inserted earlier climatological divisions it should be recalled that they evidently cannot exactly fit into the absolute chronology of the scheme, as they to a certain degree refer to a

gliding scale (cfr Sernander, 1916, p. 136). It seems most suitable, however, generally to coordinate the boreal time with the later half of finiglacial time and the very beginning of postglacial time in accordance with the conception of the climatic development arrived at through the geochronological re- cords. This also conforms to the statements made by Sernander (1915, p. 538, 1916, p. 136).

222 IVAR H O GGBOM

flora, whilst in Middle Sweden a more temperate flora immediatly conquered the ice-free land. So far geological and palaeo-botanical studies have given agreeing results. (Cfr e. g. G. De Geer, I910, Gunnar Andersson and S. Birger 1912,

p. 122, and 1914, p. 559). The relatively short period the climatic changes of which are registered by the

geochronological studies, is thus characterized by an intensifying of a warmer or more continental climate during the finiglacial time. The existence of the great terminal moraine belt, however, as well as some less conspicuous irregularities in the recession of the land-ice, proves that this development was not a continuous one. Anyhow, as there are no corresponding data of contradicting signification available from the preceding and the following times, the climatic amelioration, which caused the retreat of the ice, probably reached its greatest intensity in the

finiglacial stage. This conception of the general climatic development accords well with the in-

terpretation of the age of the dunes which has been advanced in the respective chapters of this treatise, viz. that the dunes situated within or connected with the once ice-covered area of North and Middle Europe date from this terminal phase of glacial time, the finiglacial epoch.

It remains, however, to discuss some climatological problems from the different

regions and to give some general conclusions of the climate of the time in question based on a combination of the obtained local data.

Before entering upon a review of the climatological conclusions which are to be drawn from the Fennoscandian dunes, some facts regarding the relative age of the different fields might be recalled to mind.

The knowledge of the run of the aequirecesses hitherto won does not permit an exact determination of the age of the different dune-fields. Nevertheless, it is evident that the dunes in Vtrmland and Dalarna, and also those in southern and middle Norrland, are older than the dunes in Swedish Lapland, which in reality may have been formed somewhat after the ending of the finiglacial time.

The opinions regarding the connection between the recession stages of the ice- border in Norway and in Sweden are as yet very divergent (cfr e. g. Nordhagen, 1921, pp. 87, 124). On the whole, it seems probable that at the end of fini-

glacial time the ice-remnants south of Jitmtland were far less extensive and continuous than was formerly supposed, and that the final melting away of the last ice-remnant in Norway took place at a relatively early stage of the finiglacial period. Accordingly, the Romerike dunes might be somewhat older than the dunes of the Mora-field.

Lastly, the dunes of North Finland, which lie most far away from the regions that have been geochronologically investigated, might be supposed to correspond


roughly to the same stage of the ice-border as the Middle-Swedish dunes. If

periglacial dune-drift has taken place in Karelia, as Rosberg supposed, the fields there would in fact be the oldest known of such a formation, as they are situated immediately outside the belt of terminal moraines deposited by the ice at the beginning of finiglacial time (the Salpausselkii stage).

From the above it appears that all the ancient dunes in Fennoscandia are not

synchronous, although they, except those in Swedish Lapland, have been formed before the end of finiglacial time.

Thus a map showing the direction of the dune-driving winds of Fennoscandia and of the corresponding isobars, similarly to a map showing the highest finiglacial sea-level, does not represent quite synchronous phenomena. The difference in time between the formation of the different fields is relatively small, however, and as the conclusions as to the wind-directions and the run of the isobars must be limited to comparatively rough estimates, these differences cannot greatly influence the argumentation.

In Middle Sweden and Southern Norway the dunes, the formation of which

immediately at the ice-border is most unquestionable, prove to have been blown

by winds coming almost perpendicularly from the border of the ice-remnant still

covering the inner parts of the Scandinavian peninsula. Had the only cause of these dune-driving winds been a local barometric maximum over the inland-ice, one would have expected wind-directions more to the right, whilst in reality the winds have almost coincided with the gradients from a supposed maximum of that character. In some respects the general run of the valleys may possibly have been a means of locally trending the winds in the direction mentioned; as will be shown below, however, such a deviation has probably been of no great importance. Thus it seems necessary to draw the hypothetical isobars of the time in question with a more north-south run than would be the case if no other factors had intervened than the cold center above the ice. This run of the isobars also accords with the explication given of the German dunes.

The same deviation to the left from the theoretical wind-direction, called forth

by a supposed cold center over the rest of the inland-ice, is also indicated by the dunes on the marginal deltas in Norrland and even, as far as one can judge, by the few and little known dunes in North Finland.

It is noteworthy, however, that this deviation of the winds from the direction, which would be occasioned by an atmospheric maximum alone covering the in-

land-ice, seems to be greater in the south than in the north, farther away from the great west-wind region of which the German and Polish dunes give evidence.

In this connection some further attention ought to be paid to the question how far topography may have influenced the directions of the ancient dune-driving winds in Scandinavia. The dunes in Sweden, as well as those in Romerike in

224 IVAR HO GBOM

Norway, indicate winds which have blown in the same direction as the run of the

respective valleys; thus it lies near at hand to draw conclusions as to the direct-

ing influence of the latter upon the winds. However, a map over the present frequency of different wind-directions shows at different stations that this influence

58

D 4f J# 759

I t

.0

760

6 759

76Z 761 760

A

Fig. 35. Isobars and winds in July. H, high pressure. L, low pressure. (Mainly after Mohn,

H. E. Hamberg, and Hellmann).

Fig. 36. Probable run of isobars and dominant winds in finiglacial summer. II, high pressure,

L, low pressure.

actually is very insignificant. In places, as e. g. in Dalarna, the most frequent winds in July cross the general trend of the valleys almost at right angles, in other regions often obliquely. It should be added, however, that in Dalarna and also in the interior of Northern Sweden the strongest winds, which are less frequent, come from the west and the north-west and thus blow parallel to the run of the valleys. This is also shown by the July sheet of the comprehensive maps which

Sandstr6m has compiled of the average air displacement at different stations in Europe with due regard taken not only to the frequency but also to the intensity of the winds (cfr Fig. 37). Regarding several stations, especially in Sweden,


however, Sandstr6m's map shows wind-directions which strikingly disaccord with the average run of the isobars of the month. This seems partly to be due to the fact that the calculations of the air displacements have been based upon morning observations only. Thus the incompatibility of the run of the isobars and the air

displacements in July is particularly con-

spicuous at the Bothnian coast where in

day-time, on account of the minimum then

reigning in the interior of Norrland, regularly strong southerly winds prevail, whilst

northerly ones are indicated on the map of Sandstr6m. On my map Fig. 35 of the present pressure distribution I have preferred to indicate the frequency of the

winds, but as Sandstr6m's map is most instructive regarding other regions, I re-

produce it separately on Fig. 37. The influence of topography upon the

direction of the winds must have been less on the dune-fields at the time of their formation than nowadays, as the inland-ice then levelled the topographical inequalities down to a line only some few tens of kilometers from the dune-fields.

Furthermore, there are dune-occurrences in Middle Sweden, which are even as much

exposed towards the north or north-east, from where the pure anticyclonic ice-winds would be expected, as towards the north-

west, but which nevertheless show the influence of winds coming from the latter direction. So, for instance, the dunes at

Fig. 37. Air displacements in July. The length of the arrows indicates the average displacement during 24 hours. According to Sandstrim 1918.

Gustafs are rather more exposed to the north than towards the north-west, and the dune-field at Mora lies quite unsheltered towards the north-east.

It seems thus undeniable that topography cannot alone account for the deviations of the winds on the dune-fields from the direction which would have been the result of a simple anticyclone above the remaining land-ice. On the contrary, one must conclude that in late finiglacial time the prevalent winds in Middle Swveden generally blew more or less perpendicularly out from the ice-border that is to say from the north-west.

On the other hand, it has formerly been taken for granted that the winds in

15. Geogradska Annaler 1923.

226 IVAR HO0GBOM

the time in question corresponded to a fully developed anticyclone. Furthermore, as a support for this opinion, G. De Geer1 has called the attention to the finds of erratic boulders in Viistmanland and Virmland, which have been trans-

ported by ice-bergs westwards from where they form the rock-ground, wherefore he concludes that easterly winds have prevailed. It seems most likely, however, that the ice-bergs have taken this course quite independently of the winds, as their drifting must have been much more controlled by sea-currents than by winds.

Thus, if a transport in the named direction has occurred, this would mean that the sea-currents have been directed westwards, perhaps because of the great water quantities which at that time must have passed through the outlet of the Baltic ice-sea then going over Middle Sweden westwards.

Evidently, the land-ice remnant has not only influenced the direction of the wind, but even its physical effects by intensifying its foehn-character.

We know from observations at the borders of present inland-ice regions that a dry summer climate prevails in many cases, but that nevertheless the continental winds producing it are not extraordinarily strong. This is the case, for in-

stance, in parts of West Greenland, as known from the investigations of Norden-

skj6ld (1916). Here an abnormally warm summer season is the result of the

predominant falling winds from the inland-ice. These winds are, however, not

very strong and calm often reigns, surely because of the counter-balance of the

general west-wind trend of the region. In spite of the generally insignificant intensity of the prevailing continental winds, the effect of the adiabatically warmed air is sufficient to produce for the latitude in question an unusually high summer-temperature and a drought manifested by saltish lakes without outlets and other dry-climate phenomena. At Spitzbergen, on the other hand, extreme foehn-storms sweeping down the valleys are very frequent. Especially the >)Sassen-

wind> following the Sassen-valley is known for its exceptional intensity. These winds have also given rise to >desert> phenomena, such as wind-worn pebbles, grate sculpture, salt efflorescenses, and even at places dune-drifting (cfr B. H6g- born, 1912 and C. Samuelsson, 1921). In their extreme forms the Sassen-winds are quite local phenomena; thus calm often reigns some few kilometers from where the storm is blowing at its hardest (Nansen 1920). Evidently, this character of the Spitzbergen winds is due to the sharp-cut valleys serving as narrow channels for the reestablishment of the pressure-balance between the air above the cold center presented by the inland-ice and the air above the warming sur-

rounding sea. In Scandinavia the winds may have been both strong and of high drying

capacity, both qualities furthering their sand-driving power. As, however, the dunes of Scandinavia prove to be a pure marginal formation

Cfr Geol. F6ren. F6rh. Bd 40, p. 23. Stockholm 1918.


to the receding inland-ice, their existence gives no direct evidence of a general arid climate outside the narrow zone at the ice-border, within which zone the foehn-character of the winds was maintained.

More important for a judgment of the general climatic conditions seem to be the stated directions of the dune-driving winds in Scandinavia. Therefore, I will here once more return to that subject.

I have ascribed the incompatibility of the directions found for the dune-driving winds in Scandinavia with the hypothetical anticyclonic winds at the borders of the land-ice to the general European pressure conditions manifested by the west-

erly sand-driving winds south of the Baltic. In other words, the Scandinavian

sand-driving winds show the influences not only of the cold high pressure centre

presented by the land-ice, but also of the warm low pressure centre presented by the eastern part of Europe.

In Middle and Northern Sweden, therefore, the isobars at the dune-drift time must have had a more north-south run showing a higher pressure over the still ice-covered area to the west, and a lower one to the east. The gradient must have been greater than nowadays, and neither the local low-pressure centre of South- east Norway nor the less pronounced one in Central Norrland, which develop in the summers nowadays, existed at that time.

As the difference between the present barometric pressure distribution and that influenced by the land-ice in finiglacial time, must have been most pronounced during summer, I have chosen a map of the present July isobars (Fig. 35) for a

comparison with the run of the isobars as reconstructed according to the winds which have built up the ancient dunes (Fig. 36).

The north-south direction of the dune-building winds at Romerike in Norway indicates a divergence of the isobars in southern Scandinavia. It is impossible, howewer, to judge whether this is only due to a local bend or whether the cor-

responding isobar continues bending westwards and encloses the maximum above the land-ice and probably also parts of the Norwegian Sea. Besides, in the case of the Romerike dunes the topography may really have considerably influenced the direction of the winds, as the topography there is more accentuated than in dune-

regions of Middle and North Sweden.

Before entering upon some climatological conclusions to be drawn from the dunes south of the Baltic, a few remarks might be at place regarding some recent

investigations and suggestions set forth by Scandinavian scientists of the problems connected with the climatic changes at the end of glacial time.

In a preliminary report on the climatological results of the great investigation of the peat-bogs started some years ago by the Swedish Geological Survey, von Post (i920) has advanced some new hypotheses on the climatic features of the

228 IVAR HO GBOM

boreal epoch. Basing his views on the distribution of Trapa natans and Cladium Mariscus in the different horizons of the peat-bogs, v. Post finds a change in the

type of climate from late finiglacial to early postglacial time, manifested by a more marine climate during the former, and a more continental climate during the later epoch. Without entering much upon the phyto-geographical and palaeontological facts on which these conclusions have been founded, some remarks should be made in this connection regarding the compatibility of the view that the boreal climate was a maritime one with some geological evidences, to which the attention has been called in this chapter. I have already pointed out the facts which, in

my opinion, indicate that the finiglacial epoch was characterized by a more continental climate, namely, in the first place, the rapid melting away of the landice, which

implies a low precipitation during winter and a high temperature during summer. v. Post arrives at his conclusion regarding the boreal climate from the occur-

rence of Cladium in the peat-bogs. The present geographical distribution of Cladium - which now lives in such different regions as the South Baltic countries, the valleys of the Alps, Portugal, and the Crimea - is considered to indicate that the plant needs a maritime climate for its existence. Trapa, on the other hand, is held to indicate a more continental climate during sub-boreal time, when this plant had its greatest maximum in Northern Europe. The boreal

drought, the signs of which Sundelin (1917, pp 270, 285) and others find in the low levels of the lakes, some of which would even have been without outlets, and in the brackish diatomac4-flora of some of them, v. Post regards as a conse-

quence of an anticyclone in summer over the remaining ice-remnant in Northern Sweden. Thus, according to the views of v. Post, it would be more proper to

speak of the maritime character of the boreal climate only during the cold season. The conception of a maritime winter and, consequently, a relatively great snow

precipitation, however, seems too disaccordant with the geological evidences of the climate of that time to be based on the occurrence of a hydrophilous plant, such as Cladium.

Regarding the summer climate v. Post, as mentioned, considers that an anti-

cyclone existing above Northern Sweden, which at that time was still covered with land-ice, produced east or north-east winds in the southern parts of the country. According to the dune-studies in this treatise, however, the influence of the ice- rest has not been intense enough to produce a fully developed anticyclonic wind-

system, but only interfered by deviating the winds due to general pressure conditions. Besides, it seems impossible that a drought during summer only would have caused a drying up of the lakes so that their levels sunk considerably below the pass-point of the outlets and that a seasonary evaporation would make the water brackish. Regarding the incompatibility of such variations in the level of the lakes with the explanation of the stool-layers confer A. G. Hogbom (1916).


Sundelin (1919, p. 235) distinguishes as follows the type of climate which has

prevailed in Southern Sweden from that in the middle and northern parts of the

country in late finiglacial time. D Das von dem eiserfiillten kalten baltischen Meer

hervorgerufene kiihlfeuchte 'primatlantische' Klima, das wihrend der Eisschmelze in der Kiistengegend Osterg6tlands und Smilands geherrscht zu haben scheint, wahrend ein warmtrockenes boreales Klima weiter im Innern des Landes herrschte, diirfte sich geltend gemacht haben, wenn auch immer schwicher, solange noch ein grbsserer Eisrest in Norrland vorhanden war.)) The direct evidences of the dunes do not contradict this opinion of Sundelin; on the contrary, the fact that no ancient dunes have been found within Sma'land, for instance, seems rather to support it. It has to be kept in mind, however, that dunes in that region may exist, although they have not as yet been observed. And judged from the

point of view of the general run of the isobars constructed according to the orientation of the dunes (cfr Fig. 36), the influence of the Baltic as a cold region on the distribution of the air-pressure seems to have been only of slight im-

portance.

Ahlmann and Helland-Hansen presented a couple of years ago in an interesting

study (1918) a new hypothesis for the genesis and the disappearance of the great north European land-ice.' This is not the place to enter upon a defence or a criticism of the theory as such, but some brief reflexions may be made regarding its accordance or non-accordance with the opinion of late glacial climate set forth on the preceding pages of this treatise.

The authors mentioned see the cause of the climatic deterioration that produced the Ice Age in a general upheaval of the Scandinavian peninsula and the north-eastern part of the Atlantic Basin. The effect of this movement would have been twofold; the relative sinking of the limit for the perennial snow because of the upheaval of the peninsula and the narrowing of the passage through which the Gulf-Stream enters the Norwegian Basin. Conversely, the sinking of the area in question should have caused the melting away of the land-ice.

According to the Ahlmann and Helland-Hansen theory the disappearance of the inland-ice would thus have been due to a maritime influence of a relatively warm Norwegian Sea on the adjacent parts of North Europe, a theory which seems to be almost the antithesis of the opinion I have expressed in the beginning of this chapter. However, it does not alter very much the interpretation I have given of the genesis and the age of the dunes. The acceptance of the

hypothesis of these authors mainly influences our conception of the distribution of the air pressure west of the regions in which the dunes are found; but it does not directly contradict the run of the isobars round the Baltic Sea, given

Cfr also a similar suggestion propounded by Enquist (1918, p. 107).

230 IVAR HO)GBOM

on my map Fig. 36. Hence, the two theories are in fact not so mutually con-

tradictory as could be supposed at the first glance; it is possible that the rapid melting away of the ice is due to changed temperature conditions in the Norwe-

gian Basin as well as to the development of a pronounced lowpressure region in the east of Europe during summer. The westwind-track of the German dunes

originates south-east of the Norwegian Basin; and consequently the humidity of the winds cannot have been much influenced by changes in the northern part of the Gulf Stream.

The dunes indicate a dry climate at the time of their formation, but to a certain degree strong winds may cause dune-drift at places which would have been fixed by a xerophilous vegetation if exposed only to moderate winds. It is thus

possible that dunes once formed and covered by vegetation may withstand a later dry period, provided that this period is relatively calm. The condition, however, is always that the dunes are fixed by vegetation; if this is not the case, no climate exists where such an absolute calm reigns that uncovered sand-dunes are not attacked by the winds and thus destroyed or displaced. Especially on the Mora-field in Sweden it is evident that no later sand-drift of any importance has taken place, as there neither any secondary dune-forms occur nor a re- newed wandering of the dunes has taken place. The unavoidable conclusion is thus, that at least most of the/ Middle-Swedish dunefields have been destitute of vegetation during no period since the time of the formation of the dunes. It is rather astonishing that, notwithstanding this, accidental destruction of the vegetation caused by fires or by the action of man has not for a sufficiently long time allowed the wind to disarrange the ancient dune-system.

The above conclusion regarding the continual vegetation which since finiglacial time has covered the ancient dune-fields, and especially that at Mora, seems to be of s5me importance for the reconstruction of the later climatic development also. Evidently, the interest in this respect centres on the question how far the

interpretation here given of the history of the dunes contradicts the Blytt-Ser- nander theory of the dry sub-boreal epoch. As it seems necessary to regard it as an established fact that the dunes have been covered by vegetation, it is a

purely biological question to decide whether it is possible that a general drought has ruled at the same time, manifested inter alia through numerous lakes without outlet. This question, however, may be left for the botanists and phyto-geo- graphers to answer.

In this connection the phyto-palaeontological study of Lundquist of the peat- bogs containing dune-sand in Vtstergbtland, should be recalled, as it shows that there too. the later driven dunes were fixed already in sub-boreal time, possibly whith the exception of its beginning. These dunes are also interesting as an


evidence that southerly winds predominated at the time of the great postglacial change from wet atlantic to dry sub-boreal climate. Unfortunately, similar observations from other regions most probably cannot be made, as dunes of this age have not been met with elsewhere.

It is true that the discussion on the postglacial climatic development during the last few decades has been hottest amongst the geologists of Scandinavia; but this does not mean that elsewhere the problems have got a solution. On the

contrary, the most important studies have undoubtedly been made in the northern

countries; the less pronounced difference of opinion regarding postglacial climates in the peripheric parts of the once ice-covered area is rather due to the fact that the opinions are as yet more or less individual and not grouped into schools, as in Scandinavia. This is inter alia manifested by the divergent opinions which

always are maintained amongst the German scientists concerning the exsiccation beds within the peat-bogs and other phyto-palaeontological or phyto-geographical evidences of changes in climate. And regarding the dunes it can be said, that

although they constitute so wide-spread and important a formation in Germany, they have played a very insignificant r61e in the climatological discussion. Some

attempts have been made to fit the dunes into a desirable climatic epoch, but

reversely very few conclusions have been drawn as to the climatic development from the existence and morphology of the dunes.

At first sight it is almost disappointing to find that the explanation given above

regarding the Scandinavian dunes cannot be accepted for the German ones, as the latter show every sign of having been driven by winds of a more or less

opposite direction to those which would have been a marginal phenomenon to the land-ice, when it was leaving the great plains of Germany and Poland.

Whilst the age of the Scandinavian dunes may be regarded as certain and the influence of later destructive sand-drift practically none, there is still some un-

certainty in these respects regarding the dunes south of the Baltic. This is also

clearly shown by the divergence of opinion between e. g. Tutkowski, Solger, Keilhack, and Lencevicz, previously discussed in this treatise. I will here once more return to the Solger hypothesis in order to show its untenability from a

climatological point of view, the morphological evidences being left out of consideration.

Other factors, such as the influence of continent and ocean, not taken into

account, the inland-ice, when leaving bare the dune-region of Germany and

Poland, would have called forth winds coming more from the north-east than those reconstructed from the orientation of the dunes as interpreted according to the

232 I V A R H 0 GGBO M

Solger theory, which requires direct east-winds. Particularly this is the case if Poland is considered, where the main direction of the ice-border has been about WSW-ENE.

During the warmer season there must also have been a low pressure over the ice-free continent in the south-east compared with the pressure in the north-west; and consequently the isobars could not have been determined solely by the cold center presented by the inland-ice. The winds must, therefore, have blown more southwards than corresponds to a simple inland-ice anticyclone theory. In other words, the same deviation to the left, which has been found for the periglacial winds in Scandinavia, must also have characterised the corresponding winds of an earlier epoch south of the Baltic, and probably in a still higher degree. Conse-

quently, even according to Solger's interpretation of the morphology of the German dunes, their orientation would not indicate the anticyclonic winds to be expected outside the ice-border when it was receding from the regions south of the Baltic.

Furthermore, the foehn-character could not have been so pronounced as, for

instance, in Middle Sweden, as the falling height was due only to the thickness of an ice-sheet thinning out slowly over the peripheric lowland.

Already this brief exposition tells against the Tutkowsky-Solger theory, the

untenability of which, however, most clearly appears from a study of the dune-

morphology itself, as I have demonstrated in a previous chapter. Another side of the question is, whether sand-drift took place also at the time

when the inland ice was leaving Germany and Poland, although the thereby formed dunes have since been destroyed by the later general sand-drift.

As I have briefly mentioned in the description of the German dunes, there are some few dunes the morphology of which seems to indicate winds blowing from the north. There is a possibility that these dunes may have been formed in a

periglacial situation, in which, as has been shown above, north-winds rather than east-winds are to be expected. These dunes, however, are too insignificant and too irregular to allow any general conclusions. It seems also improbable that they should have resisted the later intense sand-drift which has built up the other dunefields.

Thus it must be said that there are no direct evidences left of a periglacial dune-formation in Germany and Poland.

In this connection some attention. should be devoted to the loess question. For those who have paid no notice to the form and to the orientation of the dunes, as well as for those who have accepted the intrepretation of Solger, it is the most natural thing to connect the history of the German and the Polish dunes with that of the loess or at least of the youngest loess formation, the position of which

may indicate a late glacial age. According to the opinion advocated in this

treatise, viz. that the dunes were driven by west-winds, it is evident that there exists no connection between the ancient dunes and the loess.beds of Central Europe.


This fact is confirmed by the regional distribution of the loess-deposits south of the dune-bearing zone, quite independently of the different opinions which have been pronounced regarding the question whether the accumulations of loess on the eastward slopes of the rivers indicate that the loess-driving winds have come from the west or from the east (cfr Penck, 1906, and Leverett, 1910, p. 302).

The above conclusions refer only to the dunes in their present shape. As has

already been mentioned, a periglacial dune-drift may have taken place on the

present dune-fields, though all traces have been extinguished by the later dune- formation. There are some circumstances which seem to be in accordance with this supposition, and some which seem to be in contradiction to it. The absence as far as known of any loess-deposits east of the dune-regions corresponding to the same winds which have driven the dunes, might be explained by a previous se-

paration of the finest material from the dune-sand during the reign of periglacial winds. But this may also be ascribed to our as yet incomplete knowledge of the areas in question, where possibly a thin loess-sheet may have been overlooked. On the other hand, as Keilhack (1917) and others have pointed out, the situation of some fields clearly indicates that the sand must have been transported from the

west; and consequently the last sand-drift cannot have been only a rearranging of older dune-fields. The common form of the fields, having their greatest extension in the east-west direction, also makes a previous north-eastern drift improbable. It thus is most likely that the great loess-deposits date from earlier epochs than the ancient dune-fields described; the same is consequently the case with the wind- worn pebbles (>Dreikanter,)

often occurring below the loess. It seems nearest at hand to regard the German and Polish dunes as mainly

finiglacial and possibly early postglacial, that is to say that a continuous dune- drift went on south of the Baltic during the same time, when the dune-drift took

place where the finiglacial ice-border in Scandinavia left the marginal deltas behind

exposed to the winds from the ice. This opinion is based on several seemingly good reasons.

The German-Polish dunes not being periglacial, on account of their west.wind morphology, and, at least mainly, not being younger than neolithic from an

archaeological point of view, a relatively limited space of time remains, the climatic changes of which have to be regarded in order to form as exact an opinion as possible about their age. The decisive fact from this point of view is evidently that the same general climatic factors which called forth the rapid retreat of the ice in late-finiglacial and early postglacial time seem most suited to explain the strong west-wind system south of the Baltic. I have above set forth the facts which speak for a continental climate during that time, and such a climate must have intensified the tendency to summer west-monsuns over Europe in comparison with the corresponding winds nowadays. And further, the deviation to the east

234 I V AR H 0 GB O M

of the dune-driving foehn-like winds at the ice-border in Scandinavia, previously mentioned, indicates a general west-wind trend further southwards. Finally, the

phyto palaeontological researches have proved that the dry boreal period was followed by a more humid one, the conditions of which cannot be supposed to have been favourable for dune-formation. All these facts taken together seem un-

disputably to confirm the opinion here advocated as to the age of the dunes.

One point which may seem unexpected is, that the Baltic has not exercised

any greater influence upon the run of the isobars. This, however, is also as

striking a feature in the present distribution of the air-pressure in July, the 760 mm isobar running almost west-east, with lower pressure to the north. Very likely the corresponding isobar, however, at the end of finiglacial time made some local curve, the effect of which upon the winds fell outside the dune-regions. The fact that the Baltic at that time was partly fed by melting-water from the land-ice must not be overrated in its consequences on the distribution of the air-pressure in the summer especially during an epoch of continental climate, when the difference between the temperatures of land and sea anyhow is very great compared with the difference between a relatively warm and cold sea. Evidently the possible difference which a relatively colder Baltic at the dune-drift time would have called forth in the air-pressure compared with the present conditions, has not been

important enough to influence the winds within the German-Polish dune-regions. From the above it is to be concluded that in Germany the isobars correspond-

ing to the dune-driving winds had a run very similar to that of the July-isobars nowadays. As the winds then were sand-driving, the climate may have been drier than what is the case at present, and very probably the sand-drift was also furthered by a greater intensity of the wind at that time, caused by the greater contrasts in pressure.

It is hardly possible, however, that during the present yearly distribution of the winds in Germany dunes oriented like the ancient ones would develop if sand- drift took place nowadays, on account of the hard south-west winds in autumn, especially as this season is characterized by a far lower rainfall than summer. Most probably dunes of to-day, if formed, would have been oriented SW-NE.

A detail of interest in this connection is the asymmetric development of wind- sides and lee-sides on the wings of some horse-shoe dunes in Germany, which I have previously spoken of as indicating a change to a more southerly (WSW) wind-direction in the latest phase of the dune-drift time. This accords well with the changes in the run of the isobars, which the disappearance of the land-ice from Scandinavia must have caused.

The periglacial position of the Scandinavian dunes explains their formation even if no extremely dry climate is supposed to have existed outside the range of the


local foehn-winds from the inland-ice. On the other hand, the dunes south of the Baltic, which nowadays are everywhere practically fixed by vegetation, ex-

cept at some places in Poland, indicate a former dry period, which according to the statements in this inquiry, should correspond to the later part of finiglacial time and, possibly, the earliest postglacial time, according to the nomenclature of De Geer.

In order to get an idea of the changes compared with the present climatic conditions which must be supposed to have taken place if the dune-drift at that time is to be explained, several factors have to be considered.

Concerning the changes in the distribution of land and sea, those north of the Baltic evidently have not been of any direct importance for the aridity of the dune-driving winds south o0 the Baltic, as these winds have come from the west or north-west. On the other hand, the existence of land outside Hol- land may have been of some influence, as the west-winds at the epoch in question had to pass a longer distance over land than nowadays, and thus may have possessed a greater deficit of saturation when reaching the dune-regions. It is true that the extension of land westwards at the time in question is not per- fectly known, but it seems probable that most of the shallow North Sea was at that time part of the continent, connecting England and Denmark (Reid, 1913). This would mean that north-west winds reaching the present North Sea coast would have passed a distance similar to that between Hamburg and Berlin over land, perhaps consisting for the most part of marsh regions. Notwithstanding this character of the ground, the winds must have got somewhat warmed in comparison with the present west-winds in the same region. This difference, however, must have been of comparatively insignificant consequence. Anyhow, I have thought it worth mentioning as a local geographical factor which may have contributed to a displacement westwards of the more arid areas, now to be found in Poland and east thereof.

Lencewicz has stated that dune-drift is always going on at certain suitable places in Poland, although evidently on a small scale, and farther east dune-drift is still more common. The present 190 isotherm (not reduced to sea-level) encloses in July, extending from southern Russia, part of southern Poland, whilst the greatest part of Germany lies in July within the 18' and 17' isotherms. One may thus roughly estimate that, if temperature alone were decisive, an elevation of the

summer-temperature of at least two degrees would be needed if dune-drift were to go on in Germany at the ancient fields.

The Scandinavian phyto-palaeontologists have stated that during the climatic

optimum the summer-temperature was some two degrees higher than nowadays (cfr Gunnar Andersson 19To, G. Samuelsson 1915), but the opinions regarding the time for this climatic optimum are diverging. Sernander (191o) places it in

236 IVAR HO GBOM

sub-boreal time and Gunnar Andersson (19io) in Ancylus time, that is to say more or less at the same time as the dune-drift went on. However, one may hardly draw any strict parallels with the testimony of the dunes in this respect, as it refers to the region south of the Baltic from where no similar determinations regarding a climatic optimum are at hand.

Besides, the intensity of the winds and the amount of precipitation play such a part in the dune-building processes that any estimation of the changes in tem-

perature must be done with reservation for the influence of changes in the other climatic factors. The above reasoning regarding the run of the isotherms, however, may serve to illustrate the displacement west-wards of the climatic regions compared with nowadays, which can be supposed to have characterized the dunedrift time.

In order to demonstrate the essential climatic features in finiglacial time, I have on the preceding pages made some comparisons between the average pressure distribution in July nowadays and that which may have been reigning in finiglacial time when the dune-fields were built up.

If, on the other hand, one would seek for a type of climate nowadays, which

regarding pressure and winds shows the greatest similarities with that reconstructed for the finiglacial summer, one finds it in that which is characterized as >>Kilte- riickfille> in spring, when low pressure reigns over South-east Europe whilst North-western Scandinavia is enclosed within a high pressure region. In fact, it would not be difficult to find out a synoptical map of that type on which the direction of the isobars and the winds almost coincide with those drawn on the

map Fig. 36. The ground for this accordance seems to be that the remaining land-ice in

finiglacial time brought about a difference in temperature between Northern Scan- dinavia and East Europe similar to that which is the result of the warming up in spring nowadays, which proceeds faster in East and South-east Europe than in Scandinavia. It is very probable too, that the snow-cover in Scandinavia

remaining in that season directly influences the air pressure in the same way as did the land-ice in finiglacial time.

The comparison between this peculiar climate type of spring nowadays and that which characterized North and East Europe in finiglacial time is evidently applicable regarding the position of the high pressure and the low pressure re-

gions and the ensuing wind-directions only, whilst there are great differences in other respects. Whilst the >Kdilterickfille> are incidents in the changes of climate in spring, the similar distribution of the air pressure may have been the characteristic one during finiglacial summer. Furthermore, on account of the

greater differences in temperature between Northern Scandinavia and East Europe


at that time, the gradient may be supposed to have been greater and, conse-

quently, the winds stronger than now. The same effect might also regarding Middle Europe has been brought about

by the general displacement of the climatic zones towards the North, which can be supposed to have taken place during the probable climate optimum charac-

terizing the time in question, and on account of which the Azoric maximum, which now includes part of Europe, even more than at present, might have influenced the climate of Middle Europe.

In all probability surer and further reaching conclusions regarding the climatic

development may be based on a continued study of the dunes, if this is combined with the experiences from other branches of science. This, however, re-

quires a material of observation not yet brought together. Especially it is to be expected that examinations of peat-bogs in the ancient dune-regions, combined with the evidences of the dunes themselves about the climatic conditions, will

bring about new results. In this treatise the dunes mainly have had to speak for themselves, and only

incidentally I have brought their testimony in connection with observations of other than physico-geographical or geological character. This, I believe, also has been the most advisable in a monograph over the ancient dunes. On the other hand, for a general survey of the late quaternary climatic development the

dunes, of course, must be only a detail, the evidences of which have to be

weighed against those arrived at by other means.

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CONTENTS CHAP. PAGE.

INTRO DU CTIO N ...........................................................................

............ It 3 I. DUNE-FORMATION AND DUNE-MORPHOLOGY

.................... .............. I15

Dunes and Wave-movement ........................... .............. 15

Theory of Ripple-marks as embryonic Dunes............................. .............. 117

Theory of vthe small Obstacles>> ............................... ..

........ .............. 120

The shield-formed or the laterally extended Sand-accumulations as initial

Dunes ................................... .... ...... ............... I23 The Dune-profile ................................... ............... 125 Basal forms of Dunes

....................................................................... .. .130

Influence of alternating Winds ........................... ............... 132

Secondary Dune-forms ............................................. .......

............... 134 Characteristics and Forms of the

Dune-fields............................. .............. 136

T he D une-sand ...............................................

.................. ............... 1 37 II. ANCIENT DUNES OF FENNOSCANDIA AND DENMARK ..................... 140

Dunes in M iddle Sweden..........................................................

...............1 I42 Dunes in Southern Norway......................... ................. i56 Dunes in Northern Sweden............................. .............1 57 Dunes in Finland (and Karelia) ...............................................

.............. 170 Dunes in Southern

Sweden.............................. ................ 171 Dunes in Denmark.......

............................................ ...... .............. i772

Some remarks on recent Dune-drift in Fennoscandia................................. 173

III. DUNES SOUTH OF THE BALTIC ................ ................................... i76

D unes in G erm any .................................................................................... i8o Dunes in Poland and the Baltic

States..................................................... 203

The H ungarian D une-fields ................ ...... .................... ...................

21 i

IV. SOME CLIMATOLOGICAL CONCLUSIONS .............................................

220

L IT E R A T U R E .........................................................................

............... 238

ancient inland dunes of northern europe

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