the development of the rhine - wiley online library · the river aligned along the present courses...

The Development of the RhineAuthor(s): E. M. YatesSource: Transactions and Papers (Institute of British Geographers), No. 32 (Jun., 1963), pp. 65-81Published by: Blackwell Publishing on behalf of The Royal Geographical Society (with the Institute ofBritish Geographers)Stable URL: http://www.jstor.org/stable/621060 .Accessed: 04/08/2011 06:12

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THE DEVELOPMENT OF THE RHINE

E. M. YATES, M.SC., PH.D.

(Lecturer in Geography, University of London King's College)

Trieb nieder und nieder, Du herrlicher Rhein! Du kommst mir ja wieder, Lasst nie mich allein.

C. BRENTANO

DER RHEIN stimulates the imagination: the Vandal horde crossing the river on the last day of 406; Charlemagne's campaigns; the long struggle between France and Germany. The river has indeed played an important role in both the political and the economic history of western Europe, because it joins and provides a route between three major relief units: the Alps; the Hercynian uplands; and the north European plain (Fig. 1). Yet this link has only recently been achieved (in the geological sense). The Rhine is not an example of a superimposed river, but it is a remarkable fusion of originally distinct drainage elements. The fusion has taken place during the course of Tertiary and Quaternary time.

The Rhine Valley in Oligocene Times The period was marked by a widespread marine transgression, generally

reaching its maximum in mid-Oligocene (Stampian) times. The sea reached the northern edge of the Rhenish Uplands, entered the Cologne Bay and penetrated the Hessian Corridor to the Rhine Rift Valley.l The latter had been drowned in the lower Oligocene from the Swiss Foreland as far as the present Neckar confluence. In the mid-Oligocene, however, the southern sea reached forward to the Mainz Basin, joined the sea occupying the Hessian Corridor, and thus completed a link between the North Sea and Tethys across the present Rhine course. Another strait, close to the route now followed by the Rhine-Marne canal, may have linked the Rift Valley with the Paris Basin.2 From the Swiss Foreland a further arm of the sea, probably quite narrow, extended along the northern Alps into Bavaria. In both the Swiss Foreland and the Rhine Rift Valley very considerable deposition took place. The Oligocene beds of the Rift Valley reach a thickness of 1500 metres, and contain important reserves of salt and potash, and some oil. The 'Untere Meeresmolasse' (Stampian) of the Foreland is up to 1000 metres thick. In upper Oligocene times (Chattian) the marine deposits of the Foreland were succeeded by fresh water deposits, the 'Untere Siisswassermolasse'. The forerunners of the present Alpine headstreams of the Rhine, stimulated by the tectogenesis, contributed to this sedimentation by building great rock deltas, which now form the conglomerate 'Nagelfluh' and give rise to mountains in the Foreland such as Rigi and Speer (Fig. 1). This sedimentation blocked temporarily in upper Oligocene times (Chattian) the southern exit from the Rift

65


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FIGURE 1-The Rhine: key to places named in text.

200 1 I . I . i

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Valley. Subsequent deposition in the Rift Valley took place under fresh water or brackish conditions, leaving marls distinguished by the presence of the mussel Cyrena convexa, the 'Cyrenenmergel', and fresh water limestone distinguished by the presence of the snail Helix ramondi. In the Bavarian Strait east of the Lech some marine deposition took place in the upper Oligocene, as is demonstrated by the Promberger Beds, but these are underlain and overlain by Cyrenenmergel and show a fluctuating margin to the sea that extended from the Hungarian Basin. Marine molasse is now exposed in Bavaria along a narrow- faulted zone that marks in a tectonic sense the northern boundary of the Alps.3

In these narrow seas the Rhenish Uplands formed a broad peninsula (Fig. 2a). These Uplands are of course a remnant of the Hercynian mountains, composed of a great series of Devonian sediments, lying in a number of complicated folds. By the beginning of the Tertiary epoch the mountains had been largely reduced to a plain with rounded residual hills, the latter formed along the quartzite outcrops and giving a relief of some 200 metres. A long period of tropical or sub-tropical weathering had led to a deep decomposition of the shales, and, where this material was washed into hollows, the formation of early Tertiary clays, which are of some importance in the ceramic industry. On the plains flourished luxuriant forests, from which are derived the lignite reserves of the Rhinelands. The drainage differed considerably from that of today. The Oligocene streams have left the gravels known as the Vallendar Schotter, and from these gravels the pattern of drainage can be reconstructed (Fig. 2a). The river aligned along the present courses of the Mosel and Lahn flowed, in the reverse direction to the modern Lahn, into the Hessian Corridor.4 A distributary of this river followed the same direction as the present Rhine into the Cologne Bay.

The Vallendar Schotter rise to an altitude of 480 metres, but they are well developed upon an important 400-metre surface within the uplands, into which the Rhine, Mosel and Lahn are incised. This surface, occasionally reaching a width of 30 kilometres, is the 'Trog' of A. Philippson.5 Stratigraphically above the Vallendar Schotter, and apparently laid down under brackish conditions, are sediments derived from the products of the Tertiary weathering, the Aren- berger Beds. The late Oligocene and early Miocene appears indeed to have been a period of great sedimentation in which the old Vallendar drainage divides were buried and the streams gradually replaced by strings of salty pools. The formation of the Trog has been attributed by H. Louis to the lateral planation of the debris-laden streams responsible for the sedimentation.6 This is, however, far from being the only explanation for the formation of the Trog. Above the Trog are two further surfaces at 500 and 600 metres, the Rumpfflachen, designated respectively Rl and R2. Above these high surfaces there are residual hills, in which traces of a third surface have been distinguished at 740 to 800 metres, the R3. The higher surfaces R1, R2, R3 and the Trog have been regarded alternatively as derived from one original surface, buckled during uplift from Miocene times.7 This is supported by the presence on the Trog, in situ, of older Tertiary

G

67

Oo 00

0T1

C t- z C ~T1 cd

2

FIGURE 2a (left)-The Rhine valley in Oligocene times (Stampian); 2b (middle)-The Rhine valley in Miocene times (Helvetian); 2c (right)- The Rhine valley in Pliocene times (Astian).


weathered complexes. Evidence for buckling of the surfaces above the Trog comes from the courses of tributaries of the Mosel, such as the Kyll, which are, or appear to be, antecedent to buckling. They cross remnants of the R2 surface in their middle courses, flowing from R1 across R2 to the Trog. These interpretations suggest either an Oligocene or a Miocene age for the Trog and this latter date receives confirmation from the Westerwald where the surface is cut in basalt of lower Miocene age. Because of the presence upon it of flints the R3 surface has also been considered as Eocene or even Senonian. In general it may be said that the conflict of views on the age of the upper surfaces of the Rhenish Uplands is similar to that associated with the Welsh Uplands. A similar conflict of opinion applies to the Belgian part of the massif, the Ardennes. Both eustatic change and crustal warping have been argued as explanations for the various surfaces, including that at 400 metres. Some of the various interpretations are given by A. Godard, and in table form by J. F. Gellert.8

The coastline of the peninsula on which these developments took place fluctuated considerably during the Oligocene. In the upper Oligocene the sea withdrew from the northern shores and the swamp forests extended into the Cologne Bay. The subsidence of the latter led to the accumulation there of up to 200 metres of lignite, the brown coalfield of Cologne. On the southern shores a transgression of short duration linked the northern end of the Rhine valley with the Neuwied Basin, as shown by the presence within the Basin of the Cyrenen- mergel. This linkage, through the Bingen Gate, foreshadowed a later development of the Rhine and presumably led to changes in the already disrupted Vallendar drainage pattern. The major changes came, however, with the uplift in Miocene times and the accompanying faulting and vulcanism.

The Rhine Valley in Miocene Times Vulcanism in the Rhenish Uplands began with the formation of the andesites

and trachytes of the Siebengebirge and the Westerwald, and was followed in the Miocene by the basalt flows of the latter. The Siebengebirge, Oligocene in age, are situated at the southern apex of the Cologne Bay and are associated with its downfaulting. The massif as a whole, however, did not lift either uniformly or as an entity. The greatest uplift occurred in the south: in the Neuwied Basin, and possibly along the line of the gorge, movement was much less. The masking of the old divides by the Arenberger Beds, together with disruption associated with differential faulting, led to important changes in the drainage pattern. The reversed Lahn, the Mosel and the Rhine gathered in the Neuwied Basin and flowed northward. As well as being disrupted by the earth movements, these streams, in particular the Mosel, became superimposed, since they developed on the upper surface of the Arenberger Beds. This superimposition makes intelligible both the curious course of the Mosel, where it is incised in the Devonian outcrops on the south side of the depression of the Wittlich Sink, and its spectacular incised meanders. The Wittlich Sink had been filled by the Tertiary weathered complexes, and has subsequently been re-excavated. The

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very curious course of the Wiipper is partly explained by the adjustment of the lower stream to an infilled Oligocene valley.

The new drainage system was initially contained within the massif. The Mosel appears to have extended rapidly its course in the Mesozoic outcrops of the Trier bay, but its culminating capture of the upper Meuse in the Val de l'Asne did not occur until Pleistocene times.9

In the Alpine Foreland the Miocene was a period of great disturbance. The Alps and the Jura were elevated and the Foreland between was deepened. The movement must have begun in the upper Oligocene when a considerable deposition of molasse took place under fresh water or brackish conditions. These beds were followed by Miocene marine molasse, the 'Oberemeeres- molasse' (Burdigalian and Helvetian) as the deepening continued, and the Rhone valley and Vienna Basin were rejoined by an arm of the sea 100 kilometres wide and 600 kilometres long. The extent of the transgression is shown by an old cliff on the dip-slopes of the Swabian Jura. Continuous deposition and further movement was followed by the withdrawal of the sea in the middle and upper Miocene. The withdrawal was most rapid from Swabia. The Swiss Foreland remained occupied by an arm of the Mediterranean, and into this arm of the sea discharged the Alpine torrents, like their predecessors in Oligocene times. They laid down the coarse debris that now forms the Nagelfluh masses of Hornli and Napf. The molasse (Oligocene and Miocene) reaches a thickness of 3000 metres and varies in facies from the coarse conglomerates near to the Alps to finer material farther north. On the northern side of the Foreland, coarser material derived from the Jura is again present, the Juranagelfluh. Also, on the northern side of the Foreland, near the site of Schaffhausen, entered a major stream, known from its sands as the 'Graupensande-Strom'.10 This flowed south parallel to the Franconian Jura, and thence westward in the Swabian Foreland. The northern part of the course of the Graupensande-Strom is now that of the Main above Bamberg; the southern half is that of the Danube above Ingoldstadt. In both instances the flow was in a direction the reverse of that of today (Fig. 2b).

The lower Main probably discharged into the Mainz Basin, but the earliest Main gravels are of Pliocene age.1 The Mainz Basin was reached by an arm of the sea or a lagoon during the marine reoccupation of the Alpine Foreland (Aquitanian). In this sea were laid down considerable thicknesses of limestones and marls, the Cerithia Beds and the Corbicula Beds, which now form the hill country south-east of Bingen. Both formations have littoral facies in the north- east, showing that the Hessian corridor was no longer an arm of the sea. This former exit was further blocked in the upper Miocene and Pliocene by the basalts of Vogelsberg, the biggest basalt mass in mainland Europe, with an area of 2500 square kilometres. Farther to the east is the similar but smaller mass forming the highest point of the Rhongebirge. At the southern end of the Rift Valley the Miocene disturbances, which produced the Jura and re-elevated the Alps, had been accompanied by the vulcanicity of the Kaiserstuhl.

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On the north side of the Rhenish uplands the Rhine mouth must have been in the Cologne bay, for the mid-Miocene was a period of marine transgression, the last to reach the borders of the massif.l2 In mid-Miocene times the Rhine thus remained a Hercynian stream.

The Rhine Valley in Pliocene Times The date of the linkage of the Hercynian Rhine with the drainage of

the Rhine Rift Valley is established as Pliocene (Pontian) by the presence on the massif of the Kieseloolith Beds. A Pliocene date is ascribed to the Kieseloolith Beds because of their stratigraphical relationships in the lower Rhinelands, where they rest upon the Miocene Fischbach Beds and are in turn followed by clays containing traces of a mid-Pliocene (Astian and Piacentin) flora. The Kieseloolith Beds are pebble beds, distinguished by the very high percentage of gangue quartz and quartzite (reaching on average 98 per cent), and by the absence of pebbles derived from the rocks of the massif, for example greywacke, slate or sandstone.13 The source of the pebbles was the Triassic outcrops of the south German scarplands and of Lorraine (Lotharingia). Their presence within the massif must be associated with the southward extension of the Rhine catchment. This extension took place, in the opposite sense, along the route followed by the Oligocene transgression into the Neuwied Basin as already described, and the headward erosion presumably responsible for the extension was probably facilitated by the presence of Tertiary rocks. Within the massif the Kieseloolith Beds are associated with the Higher Terraces, the first true terraces of the Rhine. They are incised below the level of the Trog, and fall from 320 metres near Bingen to about 150 metres near the Ruhr. This fall is of course much steeper than that of the present Rhine, and is due to the continued uplift of the massif. Northward into the Netherlands the Kieseloolith Beds pass into littoral and marine facies. Owing to the subsidence of the western Netherlands the surface of the marine Pliocene reaches a depth of 600 metres whilst in the central Netherlands, Pleistocene faulting has lowered the littoral facies to depths of 300 metres.14 Even within the massif the Kieseloolith Beds have been affected by fault movements as well as uplift. In the Neuwied Basin the Higher Terraces are down-faulted some 80 metres.15 Such fault movements have also led to considerable discussion as to whether the Higher Terraces do consist of a number of distinct erosional stages or are the faulted remnants of one surface.16

The considerable changes in the north were paralleled by major changes in the south of the Rhine basin. The molasse sedimentation, which had infilled the Alpine Foreland by the end of the Miocene, together with uplift of the Jura at the western end of the Foreland, destroyed the former drainage pattern. On the northward-sloping molasse surface such Danubian headstreams as the Ill, Lech and Inn developed. The Danube was a much more powerful stream than it is today. It received the present Alpine headstreams of the Rhine, the drainage of the southern Rift Valley via an eastward-extending Aare, and possibly the upper

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Rhone.17 This former relationship of Aare and Danube is shown by the presence in Danube terrace gravels of pebbles derived from the Aare massif. The Danube tributary coming from the southern end of the rift valley left sheets of gravels derived from the Vosges. Significantly, however, in the upper Pliocene the Vosges material was overlain by debris from the Alps.18 A great reversal of drainage had taken place. The Danube had lost its upper headstreams from the Swiss Alps, and they formed a major stream that flowed through the Burgundian gate, between the Vosges and Jura, into the Rhone-Saone corridor (Fig. 2c).

During the same interval the Rhine extended its catchment area in the Rift Valley and in the south German scarplands with the aid of the Main and Neckar. Both of these tributaries had to contend with considerable tectonic movement along their courses. Uplift took place along the axis Rhon-Spessart-Odenwald, amounting to 200 metres where the axis is crossed by the Neckar.19 Con- sequently both rivers have become deeply incised and the destruction of the upwarped Mesozoic rocks was intensified. The Muschelkalk, which has a considerable outcrop south of the axis, exists north of the axis only where preserved by the basalt of Rhin. In the Odenwald even the Bunter and the thin Permian cover have been removed to expose the underlying granites and quartz porphyry. The erosion surfaces cut in the granite outcrops have been variously interpreted as exhumed surfaces of Permian age, and as piedmont surfaces (Piedmont- flachen) formed as the Mesozoic rocks were removed. South-east of the Spessart axis a 300-metre surface is present, best preserved in the Muschelkalk outcrops, the 'Gauflache', and with Pliocene clays occasionally present upon it.20 Farther south and east the highest levels of the Franconian Jura appear to be of older Tertiary age and are associated with a gravel, the 'Hochflachenschotter', which contains materials derived from the Frankenwald. The distribution of these gravels indicates an earlier drainage directed southward (Fig. 2b). These southward-flowing streams, captured during the Pliocene, now constitute the upper Main. The latter is indeed a most complex tributary of the Rhine, for its lower course is also composite. Below Miltenburg it may be considered consequent, but the sector from Gemiinden to Miltenburg is subsequent, and adjusted closely to the outcrop of the Rot (the clayey sand formation at the top of the Bunter).

This is the orthodox explanation of the development of the Main. An alternative 'Klimamorphological' interpretation has been put forward by J. Biidel, an interpretation having much in common with the ideas of Louis on the formation of the Trog.21 Biidel suggests that both the present Main course and the Gauflache are best understood as the products of the tropical climates of Pliocene times. Under such climates, with associated rapid chemical weathering, streams lack the angular rock waste they require to incise. As a result the streams are wide and shallow, and experience in time of flood many major changes of course. By such changes and the abstraction of the formerly southward-flowing streams, the present Main was formed. With the onset of colder conditions in the Pleistocene, mechanical weathering became more important than chemical

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weathering. The Main, now carrying angular rock fragments, was able to incise, forming the present steep-sided valley.

Similarly the course of the Neckar has been variously explained. It has been considered a successful pirate stream which beheaded a series of streams formerly flowing south-east across the Alb to the Danube. The north-east- flowing section of the Neckar near Stuttgart is a reversed section of one such stream.22 The section of the Neckar above Tiibingen may be regarded as a strike stream, similar to the Main between Gemiinden and Miltenburg but adjusted to the outcrop of the Gipskeuper and Lettenkohle. Alternatively the Neckar has been considered largely the result of the tectonics that flexured the south German scarplands. The Spessart axis is paralleled to the south by a further axis extending east-north-east from the Black Forest. On the northern slopes of this southern axis developed the Neckar, turning into the basin between the two axes at Eberbach.23

This emphasis upon tectonic effects and the various references to ante- cedence may appear strange to English geographers; but it is important to note that such uplifts as that of the Black Forest and the consequent warping of the south German scarplands continued in Pleistocene and in Holocene times. The recent nature of the movements is shown by the various levels at which cirques of Wiirm age are now to be found in the Black Forest. Obviously the drainage must have been either antecedent to or deflected by the movement. The tectonic explanation of the Neckar course is similar to that made originally by W. Penck.24 He considered that the Neckar occupied a depression between two separate areas of uplift, the Alb or Swabian Jura, and the Black Forest. The present headstreams were antecedent to the later more pronounced uplift of the southern Alb.

The success of both the Neckar and the Main in capturing the streams flowing towards the Swabian Foreland is due of course to the rejuvenation consequent upon the lowering of their base-level with the continued downfaulting of the Rift Valley. This movement continued in the Pliocene, and some 150 metres of Pliocene deposits are present in the Mainz Basin, but the most rapid period of movement appears to have come at the end of Pliocene times.25 Not only the Rhine Rift Valley was affected. The northern end of the Rhine Rift Valley, the Mainz Basin, is paralleled to the east by the Aschaffenburg Basin, from which it is separated by the Frankfurt Horst. The Aschaffenburg Basin developed in the Pliocene, and its movements diverted the lower Main northwards.

The Rhine Valley in Pleistocene Times

By the beginning of the Quaternary era only the Alpine part of the present Rhine drainage remained unconnected with the major stream. The structural elements already connected by the Rhine at the end of the Tertiary era were the Lower Rhinelands, the Rhenish Uplands and the Rhine Rift Valley. The first and the third of these elements were affected by downward movement throughout

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the Pleistocene whilst the elevation of the Rhenish Uplands continued con- temporaneously.

Across the rising massif the Rhine has cut its gorge, but the downcutting has been spasmodic. Beneath the Higher Terraces, with their Kieseloolith gravels, is present a great suite of terraces: the High Terrace; the Middle Terrace; the Low Terrace. Each of these terraces is in fact composite and consists of some two or three distinct stages. There are, for example, Upper, Middle and Lower Middle Terraces. Furthermore the terraces have been warped and faulted, especially in the vicinity of the Neuwied Basin where volcanic activity occurred in the late Pleistocene and in Holocene times. Consequently the terrace sequence is extraordinarily complicated, and there exists a considerable difference of opinion on the identification of the various terrace levels.26

The lifting of the massif has given the upper terraces a much steeper fall northward than the present Rhine, and the older the terrace the greater the fall. The Middle High Terrace is at an altitude of 220 metres at Rochusberg im- mediately south of the massif. It rises to 265 metres at Trechlinghausen within the gorge, and then falls northward.27 Within the Neuwied Basin it is probably below 100 metres and is thickly covered with loess and tuff. At Andernach it is at 220 metres; at Linz 210 metres; at Duisburg 100 metres. In contrast the Low Terrace is at 60 metres at Andernach and at 30 metres at Krefeld. This is a much gentler fall northward and as a result the terraces cross in the vicinity of Nijmegen, the High Terrace gravels descending beneath those of the Low Terrace.28

In the lower Rhinelands the oldest of the High Terrace gravels, also known as the 'Alteste Diluvialschotter', are followed stratigraphically by the Tegelian Beds and their marine equivalents, part of the Icenian Beds. The latter reach a thickness of 200 metres and are evidence of a continued subsidence. This downward movement was not uniform, however. The underlying Mesozoic and Paleozoic rocks are much faulted in a north-north-west to south-south-east direction and form, beneath the Rhine gravels, a series of horsts and graben. Movement along some of these fault lines took place during the Pleistocene. The High Terrace in the Cologne Bay is faulted and presents to the east a steep fault scarp, the Ville Ridge. This faulting is of considerable importance to the brown coal industry of the Bay since it is in such horsts that the lignite approaches close to the surface. Similarly the relative uplift of the Peel Horst in the Nether- lands brings the Carboniferous rocks closer to the surface, and is of importance in the hard coal industry. The Tegelian Beds, famous for their rich fauna, probably belong to an early interglacial, and this introduces the vexed problem of chronology.

The problem is a difficult one because three theories have been advanced of the formation of the terraces: tectonic; glacial-eustatic; and climatic. The tectonic theory was developed by H. Quiring who saw the faulting of the lower Rhinelands as the major cause of the terrace formation.29 The climatic theory, derived initially from the work of A. Penck and E. Bruckner in the Alps,30 is

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dependent upon the view that in glacial times the great quantity of weathered material that becomes available is in excess of the transportative power of the streams. The surplus material is spread in aggradational terraces. Applied to the lower Rhine terraces this theory, sometimes in a modified form, has had a number of exponents.31 The glacial-eustatic interpretation of the lower Rhine terraces was first put forward by R. Grahmann, and was stimulated by work on the terrace systems of the Somme and Thames.32 Recently, however, the gravels of the terraces below and including the High Terrace have been distinguished from the Kieseloolith gravels, and dated as glacial,33 on the following grounds: lack of leaching; presence of cryoturbations; presence of large boulders, which it is considered must have been transported by ice floes; presence of uncemented sand blocks which must have been transported in a frozen state; and the degree of 'rounding' of the individual pebbles.34 Some further evidence of the glacial date of the terraces is to be seen in the relationship between the terraces of the Rhine and the Ruhr, and the moraine of the Saale ice. This was the only ice advance to reach the Lower Rhinelands (and the Rhine must then have had a regime like one of the present Siberian rivers). The ice overran the Rhine terraces and pushed up a remarkable morainic wall, the 'Stauchmorine', which extends from Krefeld via Apeldoorn to the Zuider Zee and forms part of the Amersfoorter stadium.35 This feature is built largely of Rhine gravels but contains also a small quantity of material derived from the north.36 In places outwash sand and ground moraine associated with the Saale advance rest on the Middle Terrace, and on the Ruhr small quantities of northern material have been incorporated in the Lower Middle Terrace gravels.37 It would appear, therefore, that the terrace formation and the ice advance were contemporaneous. The Lower Middle Terrace is considered to be of Saale age (Riss) and the Upper Low Terrace Weichsel (Wiirm). Some further evidence for the Saale age of the Lower Middle Terrace comes from the Krefeld area. There substantial fragments of this Terrace remain on the western side of the push moraine. They were formed by the Rhine after it had been deflected westward by the ice, and before it broke back through the moraine to its present position. Beneath the Terrace is a buried 'Rinne' (meander) of the Rhine, the floor of which descends to sea-level. The Rinne is infilled with gravel, but in places on the gravel is a peat which pollen analysis has shown to be of Holstein age (Elster-Saale interglacial). This again suggests a Saale age for the Middle Terrace. The Rinne itself may be of Elster age and its depth is interpreted as an eustatic effect.

The presence of the Holstein pollen is crucial to the dating of the Rinne near Krefeld, for deep Rinnen are also present in the Dutch Rhinelands, reaching depths of 40 metres below sea-level in the Gelder valley and 100 metres below sea-level in the Ijssel valley. These Rinnen are considered to have been formed by glacial erosion and not to be due to a rejuvenation of the Rhine following eustatic change for the following reasons:

(1) The Rinnen did not guide the ice lobes and therefore could not have existed before the arrival of the ice.

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(2) They descend to different depths. (3) The fall in sea-level in glacial times would have been accompanied by a

great extension of the river. In Weichsel times, for example, the sea-level fell by 86 metres but the Rhine course was extended by 700-800 kilometres. Only on steep coasts would eustatic effects cause incision by the streams, and the course of the Low Terrace shows that this did not take place along the Rhine.38

In view of these contrasting explanations the problem of eustatic effects on the Rhine remains extremely puzzling. Studies of the gravels and of the Stauch- morane provide evidence of a glacial rather than inter-glacial age for the terraces, but do not prove that the terraces owe their origin solely to the degeneration of the climate and to the lack of vegetation which might prevent weathering: in other words, to glacial aggradation. It would appear reasonable to assume that all the various causal factors considered contributed to the formation of the terraces. H. W. Quitzow, who adopts broadly the tectonic view for the incision, accepts a climatic explanation for the terrace development.39 K. Kaiser, although he does not accept the tectonic interpretation, briefly discusses possible isostatic compensation beyond the ice rim. This would mean a contemporaneity of tectonic and climatic effects. A comparison with the Danube is of value. The number of terraces present in the Hungarian Middle Mountains (Bakony Wald) exceeds that downstream in the Great Alfold. This would appear to be due to crustal movement. Furthermore it is difficult to see any climatic explanation for the presence of Danube terraces at 200 metres in the Middle Mountains when, in the Little Alfold and the Great Alfold, Danube gravels descend to below 100 metres beneath sea-level.40 Similar crustal movements, continuing until well into the Pleistocene, are clearly in evidence in the Rhenish Uplands and Cologne Bay.41 The conclusion seems in- escapable, therefore, that tectonic forces have been of major importance in the development of the Rhine terraces. Indeed, in view of Kaiser's careful study of the High Terrace gravels and of Louis's work on the Trog, it would appear that terraces have been formed under a variety of climatic conditions. In general it may be said that climate (in the sense described), tectonic forces, and glacial- eustatic change have all contributed to the formation of the Rhine terraces, but the role played by the crustal movements was a major one. In view of the excessive claims made by some 'Klimamorphologists' O. Maull's comment is readily understandable. When discussing the relative contribution of tectonic forces and 'climate' to the relief of the Rhenish uplands and the Alps he observes 'Obwohl die verschiedensten Klimate an ihnen geformt haben, wenn auch ungleich intensiver, der Art nach doch nur so wie das Klima an den Formen des Kolner Doms'. ('Therefore different climates have fashioned them, if with unequal intensity, only as much as climate contributes to the form of Cologne Cathedral'.) On the other hand Biidel, as an exponent of Klimamorphologie, writes 'Alterbte tektonische Strukturen, die an der Oberflache durch die Auslese

76


harter und weicher Schichten "petrographische" sichtbar werden, oder jung tektonische Vorgange, die die Erdkruste zerrechen, zerreissen oder sonst deformieren, sind in diesem gesetzmassig an die Klimazonen geknupften Bild nur Stirungen Arabesken und-wenn auch oft sehr auffallige-Ausnahmen'. ('Ancient structures that become visible on the surface owing to differential erosion of beds of varying resistance, or recent tectonic events that break, tear or deform the earth's crust, are to the morphology associated with climatic zones only disturbances, arabesques and, even if very striking, exceptions.')42

To return to the chronology of the terraces, it is to be noted that an accurate date can be given to the Lower Low Terrace. It contains pumice from the late Pleistocene vulcanism of the Neuwied Basin and has therefore been formed subsequent to the Allerod period, that is subsequent to about 11,000 B.C. In other words it is of Holocene age, the latest of the long series of terraces and surfaces within the Rhenish Uplands which extend in age from the Oligocene to the Holocene.

The occupation by the ice of the Amersfoorter stadium must have deflected the Rhine mouths westward. The distribution of Eemian deposits (Saale-Weichsel interglacial) suggests that after the deflection the exits were the Ijssel and Geld valleys. In the Weichsel glaciation the northern North Sea was again occupied by ice. Before the ice-sheet was complete the fall of sea-level would have led to an extension of the Rhine. Eventually, however, the ice extended from north-east England to Denmark. Thames and Rhine water was ponded up by the ice and escaped south via the Straits of Dover.43 Such ponding probably also took place in the Saale glaciation when the ice reached further south, and this may have been responsible for the initial formation of the Straits.44 An older extension of the Rhine across the floor of the present North Sea may be shown by the Chillesford Crag of East Anglia. The crag contains mica, the source region of which is believed to be the Ardennes.45

The formation of the straits of Dover has much changed tidal conditions, and under the influence of the tides the more south-westerly distributaries of the Rhine have experienced stronger scour than those of the north-east. The greater part of the Rhine discharge has been diverted further south-west in historical times, the deflection of the Waal above Dordrecht occurring on the 18 November 1421.46 Factors contributory to the decline of the north-eastern distributaries may be the rise in sea-level, and local alluviation.47

Within the Rhine Rift Valley considerable downward movement continued during the Pleistocene. The Quaternary gravels reach great thicknesses: 397 metres has been recorded in a bore at Heidelberg.48 This has had a profound effect on the terrace formation. Whereas in the Rhenish Uplands the oldest terraces are the highest, in the Rift Valley the floor is occupied by the Low Terrace and the flood-plain, and their gravels lie above those of the buried older terraces.49 Older terrace remnants are found above the Low Terrace only on the sides of the Rift Valley and on the Hessian Hills. Even so the height of these remnants varies considerably according to the extent of the downward move-

77


ment. Old terrace gravels (of the Higher Terrace) lie at 35-40 metres above the present stream at Biebrich north of Mainz. In the Rhein-Hesse Hills they are at 140 metres above the Rhine.50 The terraces, as in the Rhenish Uplands, are considered to be of glacial rather than interglacial date, formed by the aggradation of the Rhine when it was heavily laden with glacial debris. The Low Terrace is considered to be of Wiirm age and the Middle Terrace of Riss age. The Rhine terraces thus provide a link between the Saale glaciation of the North German Plain and the Riss glaciation of the Alps. The presence of lakes in the Alpine Foreland during interglacial periods is thought to be additional evidence of a glacial rather than interglacial date, since lakes reduce the volume of material entering the Rift Valley and inhibit the development of aggradational terraces. The Low Terrace has a considerable slope from 148 metres at Strasbourg to 86 metres at Mainz. At Schaffhausen the Upper Low Terrace is at 385 metres. The steep slope of the terrace northward is partly due to the sorting of the gravels since the finer material has been carried farther downstream. Near Frankfurt there is a considerable development of blown sand, whilst the gravels in the Sundgau at the southern end of the Rift Valley contain large cobbles. As well as descending steeply northwards the Low Terrace also descends relative to the Rhine. It is 20 metres above the river at Basle, and 5 metres at Mainz.51 In Switzerland the relationship of the terrace with the moraines shows it to be of Wiirm age. But the Upper Low Terrace does not correspond with the Young Moraine. It must rather be dated as Friihwiirm. Any associated moraine would lie nearer to the Alps than the Young Moraine (which is of Hochwiirm age) and has yet to be identified.52 Leeman, however, came to the conclusion that near Schaffhausen the Upper Low Terrace is aggradational whilst the Lower Low Terrace is erosional. This is at variance with the sequence in the Rhenish uplands, and may mean that the correlation of fragments of terraces, even over a short stretch of the stream as near Schaffhausen, is impossible because many separate causes have led to the formation of terraces, and these causes have been independently operative.53

The movements in the Rift Valley also contributed to the most marked change of all. In Pliocene times, as noted, the Alpine Rhine flowed through the Belfort Gap. In that gap and in the Sundgau is present a great sheet of gravels, 20 kilometres or more wide and 15 to 20 metres thick.54 These gravels were laid down by the Alpine Rhine (they are rich in rocks from the Aare massif) and the width of the deposit shows the gradual deflection of this stream northwards as the Rift Valley subsided. This subsidence, coupled with the headward erosion of the Rift Valley Rhine, brought about the linkage of the Alpine part of the Rhine with the main stream. The link was completed at the beginning of the Pleisto- cene. The Vorder Rhine, however, was not then one of the headstreams of the Rhine, but flowed to the Danube. The westward turn of the Vorder Rhine into the Boden Sea, which contrasts sharply with the simpler courses of the Ill, Lech and Inn, was due to the Pliocene-Pleistocene faulting in the molasse, for the lake occupies a minor graben.55 The change in direction of the Vorder Rhine,

78


that is its junction with the main Rhine rather than the Danube, came in the Riss-Wiirm interglacial. The advance of the ice into the Alpine Foreland caused a further notable change. The post-Wiirm Rhine has not succeeded in re-occupying its old course at Schaffhausen. The new course descends over an outcrop of Jurassic limestone in the spectacular Rhine fall.56

Also in the Wiirm occurred one of the most spectacular captures associated with the Rhine-Danube struggle-that of the Wutach at Blomberg. In mid- Pliocene times the Aare, as already described, was a headstream of the Danube, and followed a course in the direction of the lower Wutach, receiving the upper Wutach near Blomberg as a tributary. This old course of the Aare can be traced by means of gravels near Blomberg containing rocks of Alpine origin. In the upper Pliocene the Aare was lost by the Danube and the present lower Wutach began as a small reversed stream in the abandoned section of the Aare valley. By headward erosion this small stream cut back and beheaded the Danube. From the elbow of capture the Wutach falls to the Rhine in 38 kilometres making its confluence at an altitude of 313 metres. The beheaded Danube flows 370 kilometres before reaching the same altitude.57 Even this does not complete the tally of the losses of the Danube to the Rhine. From the Danube valley near Tuttlingen a considerable volume of water is lost into the Jurassic limestones, and this reappears in the great spring at Aach, from whence it flows into the Boden Sea and the Rhine.

Thus was formed the Rhine. Of all the rivers of western Europe it is the only one to join the Alps with Hercynian Europe and the North European Plain, but its importance does not rest solely there. The combination of these relief and structural elements, with their differing hydrological regimes, has given the river an unusually regular flow. The river crosses one of the major coalfields of Europe, and its delta has an unmatched centrality for the nation states of western Europe. The geological events described have fashioned both a river and an artery of trade endowed with unparalleled advantages.

ACKNOWLEDGMENT

The author gratefully acknowledges the grant made by his college, King's College, London, towards the cost of the illustrations.

NOTES

1 R. HUNGER, Brockhaus Taschenbuch der Geologie (Berlin, 1955), 336-50. 2 C. MORDZIOL, Der geologische Werdegang des Mittelrheintales. (Wittlich, 1951), 14; M.

GIGNOUX, Geologie stratigraphique (Paris, 1926), 413. 3 C. TROLL, 'Der Diluviale Inn-Chiemsee-Gletscher', Forschungen zur deutschen Landeskunde, 23

(1924), 1-121. 4 W. KLUPFEL, 'Zur Entstehung des Rheinsystems', Zeitschrift der deutschen Geologischen Gesell-

schaft, 83 (1931), 597-611. 5 A. PHILIPPSON, 'Entwicklunggeschichte des Rheinischen Schiefergebirge', Sitzung Berichte der

Niederrheinische Gesellschaft fur Natur- und Heimatkunde, 1899A (1899), 48-50.

79


6 H. Louis, 'Ober die altere Formenentwicklung im Rheinischen Schiefergebirge, inbesondere im Moselgebiet', Munchner Geographische Hefte, 2 (1953), 1-97.

7 C. MORDZIOL, op. cit., 52. 8 J. F. GELLERT, Grundziige der physischen Geographie von Deutschland (Berlin, 1958), 84; A.

GODARD, 'Morphologie des socles et des massifs anciens', Revue Geographique de l'Est, 1 (1962), 79-96. 9 P. GEORGE and J. TRICART, L'Europe Centrale, vol. 1. (Paris, 1954), 52-65. 10 E. HENNIG, 'Entwicklung des Schweizer Flussnetzes', Geographica Helvetica, 4 (1949), 11-16. 11 H. SCHREPFER, 'Das Maintal zwischen Spessart und Odenwald', Forschungen zur deutschen

Landeskunde, 23 (1924), 191-224. 12 P. KUKUK, Geologie des Niederrheinisch Westfalischen Steinkohlengebietes (Berlin, 1938), 477;

A. J. PANNAKOEK, Geological history of the Netherlands (The Hague, 1956), 65. 13 K. KAISER, 'Geologischen Untersuchungen iuber die Hauptterrasse in der Niederrheinischen

Bucht', Sonderveriffentlichungen des Geologischen Institutes der Universitdt Koln, 1 (1956), 1-68. 14 A. J. PANNAKOEK, op. cit., 69; P. WOLDSTEDT, Das Eiszeitalter, 2 (1958), 59. 15 M. HOPMANN, G. KNETSCH and J. FRECHEN, Die Vulcanische Eifel (Wittlich, 1951), 23. 16 H. BREDDIN, 'Die Hohenterrassen von Rhein und Ruhr am Rande des Bergischen Landes',

Jahrbuch der preussischen Geologischen Landesanstalt, 49 (1928), 501-50; K. KAISER, op. cit. 17 W. STAUB, Pliozine Verebnungen und Flusslaufe in den Schweizerischen Zentralalpen',

Erdkunde, 11 (1957), 124-8. 18 E. HENNIG, op. cit. 19 H. SCHNEIDER, 'Morphologie des Buntsandsteinodenenwaldes', Frankfurter Geographische

Hefte, 6 (1932), 1-76. 20 H. SCHREPFER, op. cit. 21 J. BUDEL, 'Grunzuge der Klimamorphologischen Entwicklung Frankens', Wurzburger

Geographische Arbeiten, 4 (1957), 5-46. 22 W. STROEBEL, Erlauterung zur Geologischen Karte von Stuttgart und Umgebung (1959),

chapter 4, 'Landschaftgeschichte'. 23 A. ZIENERT, 'Die Grossformen des Schwarzwaldes', Forschungen zur deutschen Landeskinde,

128 (1961), 1-108. 24 W. PENCK, 'Die Piedmontflachen des Sudlichen Schwarzwaldes', Zeitschrift der Gesellschaft

fur Erdkunde zu Berlin, 3 (1925), 81-108. 25 J. P. BAKKER, 'Einage Probleme der Morpholdgie und der jiingsten geologischen Geschichte

des Mainzer Becken und seiner Umgebung', Geographische en Geologische Mededeelingen, 3 (1930), 1-112.

26 G. SITTIG, 'Le probleme des "terrasses fluviales" a propos d'une vallee du Masif Schisteux Rhenan', Annales de Geographie, 45 (1936), 136-49.

27 D. GURLITT, 'Das Mittelrheintal: Formen und Gestalt', Forschungen zur deutschen Landeskunde, 46 (1949), 1-159.

28 P. WOLDSTEDT, op. cit. 29 H. QUIRING, Ober die tektonischen Grundlagen der Flussterrassenbildung', Zeitschrift der

deutschen Geologischen Gesellschaft, 78 (1926), 156-63. 30 A. PENCK and E. BRUCKNER, Die Alpen im Eiszeitalter (1909). 31 W. SOERGEL, 'Das Diluviale System, Die geologische Grundlage der Vollgleiderung des

Eiszeitalters', Forschritte der Geologie und Palaeontologie, 12 (1939), 155-283; K. TROLL, 'Tiefen- erosion, Seitenerosion und Akkumulation der Fliisse im fluvioglazialen und periglazialen Bereich', Geomorphologischen Studien (1959), 213-27.

32 R. GRAHMANN, Zur Gliederung des Quartars am Mittel- und Niederrhein Zeitschrift der deutschen Geologischen Gesellschaft, 96 (1944), 149-55.

33 K. KAISER, op. cit. 34 The use of the degree of 'roundness' in pebbles in the analysis of gravels has been developed

by A. Cailleux and is clearly described by J. TRICART and R. SCHAEFFER 'L'indice d'emousse des galets: moyen d'etude des systemes d'6rosion', Rdvue de Geomorphologie Dynamique, 4 (1950), 151-79.

35 P. WOLDSTEDT, op. cit., A. J. PANNAKOEK, op. cit. 36 A. GUILCHER and A. CAILLEUX, 'Reliefs et Formations Quarternaires du Centre-est des Pays-

Bas', Revue de Gdomorphologie Dynamique, 3 (1950), 128-43. 37 K. KAISER, 'Die Hohenterrassen der Bergischen Randh6hen und die Eisrandbildungen an der

Ruhr', Sonderveroffentlichungen des Geologischen Institutes der Universitdt Koln, 2 (1957). 38 K. N. THOME, 'Eisvorstoss und Flussregime an Niederrhein und Zuider Zee in Jung-Pleistozan',

in Pliozdn and Pleistozdn am Mittel und Nierderrhein (Krefeld, 1959), 197-246.

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THE DEVELOPMENT OF THE RHINE 81

39 H. W. QUITZOW, 'Die Terrassengliederung im Niederrheinischen Tieflands.' Geologie en Mijnbouw, 18, New Series (1956), 357-73.

40 M. PECSI, 'Das Ausmass der quartairen tektonischen Bewegungen im ungarischen Abschnitt des Donautales', Petermann's Geographischen Mitteilungen, 102 (1958) 274-80.

41 J. FRECHEN and C. MORDZIOL, Der Rheinische Bimsstein (1953), 14. 42 0. MAULL, Handbuch der Geomorphologie, 2nd edition (Vienna, 1958), 27; J. BijDEL, op. cit., 7. 43 H. VALENTIN, 'Glazialmorphologische Untersuchungen in Ostengland', Abhandlungen des

Geographischen Instituts der Freien Universitit Berlin, 4 (1957), 1-86. 44 L. D. STAMP, 'The geographical evolution of the North Sea Basin', Journal du Conseil Inter-

nationalpour l'exploration de la mer, 11 (1936), 135-63. 45 F. W. HARMER, 'The Pliocene deposits of the eastern counties of England', Jubilee volume of the

Geological Association (1909), 88-102. 46 K. N. THOME, op. cit. 47 A. J. PANNAKOEK, op. cit., 119. 48 J. P. BAKKER, op. cit. 49 F. KLUTE and W. WILL, 'Terrassenbildung und Erosion des mittleren Rheingebeits in ihrer

Abhangigkeit von Tektonik und Klima des Diluviums', Petermann's Geographischen Mitteilungen, 80 (1934), 144-7.

50 0. SCHMIDTGEN and W. WAGNER, 'Bericht iiber die Begehungen der Hauptversammlung in Mainz', Zeitschrift der deutschen Geologischen Gesellschaft, 83 (1931), 671-94.

51 E. JUILLERT, 'Une carte des formes du relief dans la plaine d'Alsace-Bade', L'information geographique, 13 (1949), 116-20.

52 0. WITTMAN, 'Die Niederterrassenfelder im Umkreis von Basel und ihre Kartographische Darstellung', Regio Basiliensis, 3 (1961), 1-46.

53 A. LEEMAN, 'Revision der Wiirmterrassen im Rheintal zwischen Diessenhofen und Koblenz', Geographica Helvetica 13 (1958), 89-173 (note that the Koblenz to which reference is made in the title is in Switzerland).

54 I. SCHAEFFER, 'Geomorphologische Analyse des Elsiissischen Sundgaus', Geomorphologischen Studien (1957), 157-83.

55 J. F. GELLERT, op. cit., 181. 56 H. HUBER, 'Ablagerungen aus der Wiirmzeit im Rheintal zwischen Bondensee und Aare',

Vierteljahrschrift der Naturforschenden Gessellschaft in Zurich, 1 (1956), 1-92; G. WAGNER, Einfuhrung in die Erd- und Landschaftgeschichte, 3rd edition (1960), 74.

57 R. METZ and G. REIN, 'Erlauterung zur geologisch-petrographischen Ubersichts Karte des Sudschwarzwaldes (Lahr, 1958).

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