fossil shells from wexford and manxland

Fossil Shells from Wexford and ManxlandAuthor(s): Alfred BellSource: The Irish Naturalist, Vol. 28, No. 10 (Oct., 1919), pp. 109-114Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25524871 .

Accessed: 14/06/2014 06:09

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Irish Naturalists' Journal Ltd. is collaborating with JSTOR to digitize, preserve and extend access to The IrishNaturalist.

http://www.jstor.org

This content downloaded from 185.44.77.62 on Sat, 14 Jun 2014 06:09:20 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=inj

http://www.jstor.org/stable/25524871?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


Oct. igig. The Irish Naturalist. 109

FOSSIL SHELLS FROM WEXFORD AND MANXLAND.

BY ALFRED BELL.

When presenting the Reports on the Manure Gravels of Co.

Wexford to the British Association in 1887-1890, it appeared to the writer that the theory of their glacial origin was not

well founded, nor borne out by their faunal contents, nor

by the way in which these were distributed; and this opinion was confirmed later, when, visiting the country to the north of the Peel-Ramsey line in the Isle of Man, he saw that the same conditions prevailed there, not only in the strati

graphical arrangement, but equally so in the fossils yielded

by the clays and sands exposed in this area. Subsequent researches have intensified this conviction. According to

Mr. Hallissy,1 the basal bed of this series is a highly cal careous chocolate-coloured clay or marl (laid down by the Irish Channel ice), which occurs over practically the whole

district, succeeded by shelly gravel and finely stratified sand, the whole capped by a

" stratum

" of calcareous clay marl

of a drab colour (Griffiths). This order also prevails in the Isle of Man just referred to,

where, according to Prof. Kendall2, the lower bed of dun

coloured Boulder-clay contains a large quantity of small

stones, frequently well glaciated, and a great abundance of shells in a fair state of preservation ; this agreeing with the contents of the Wexford marls. The Manx clays vary in texture from stony till to fine buttery clay.

At one place Prof. Kendall met with a bed of fine tough

clay unlike any of the drift beds in the Irish Sea basin with

which he was acquainted, containing a well-preserved boreal fauna, many of the bivalves having their valves still in apposition. In this particular clay were one or two seams

of gravel which seemed to show signs of having been involved in the clay by some kneading or shearing movement sub

sequent to its formation. A very similar arrangement is

present in the Holderness clays on the Yorkshire coast.3

1 Hallissy, T. : On the superficial deposits of the County of Wexfcrd.

Irish Naturalist, Vol. xxi., p. 175, 1912. 2

Kendall, P. F., Yn Lioar Manninagh, vol. i., p. 398, 1894. 3

Bell, A., Naturalist (Yorkshire), 1918.

A



110 The Irish Naturalist. Oct.,

One of these seams, Professor Kendall states, contained

many shells, mostly species of Trophon, such as T. scalar i~

forme and its kindred, and this genus is very prolific both

specifically and individually in the Wexford gravels, es

pecially in the Blackwater cliffs on the coast.

The bed of sand overlying this clayey gravel is "

certainly suggestive of regular and horizontal stratification

" (Kendall,

loc. cit.). Further northwards the cliffs rise near Cranstal Point to 270 feet.

The fine sands seen in these cliffs are of the same texture

and like those in the valley of the Slaney river, Wexford, contain a few large boulders. One of these recorded in

my Wexford Report1 had evidently fallen from above as if

dropped from a passing ice-floe, as it had disturbed and

compressed the laminated sands into which it had fallen. As at Pulregan, Wexford, the foot of Cranstal cliffs yield a

harvest of shells weathered out from above.

It was further noticed upon comparing the fossils from the two districts, i.e., Wexford and the Isle of Man, that

both contained many species and generic types in common

not found elsewhere in the Irish Sea area, including a number

of forms either extinct or new to science, and many species still living in either Southern or Northern Europe, but not

in the present Irish Sea basin. The Wexford gravels, etc., have yielded up to the present about 200 species ; those of the Isle of Man, 145 species. Of the shells common to both

localities, there are either extinct or new to science, n ; Southern Europe, 2 ; Northern Europe, 19 ; and Celtic, 59

species.

The combined faunas of the two areas make up a total of more than 260 species, which may be grouped as follows :?

Ireland. Isle of Man.

Extinct or new to science 53 26 41 Southern Europe 27 22 5 Northern Europe 63 55 24 Celtic (British) .. 119 103 75

262 206 145

x Report, British Association, op. cit., 1888.



I9I9- Bell.?Fossil Shells from Wexford and Manxland. 111

Many of the extinct forms are of Pliocene origin, and Prof.

Cole has noted the occurrence of iron-stained shells in the

drifts of Co. Carlow, and cites them as fair evidence of the

existence of Pliocene deposits in Ireland.1

The condition or preservation of the shells is to some

extent governed by the nature of the matrix they occur in. Where they are found in clay they may be presumed,

especially those bivalves that have the valves united, to be in situ, while those from the gravel show signs of

transport and rough treatment, but not to any great extent.

Most of the bivalves are broken into angular fragments, often of large size, with a clean and sharp fracture. The

larger Gasteropods have usually lost their apices, the

Neptuneae and the Buccina much of their outer surface by exfoliation. These occur from just hatched individuals to

others of great age. The Purpuras have suffered from the

attacks of a boring sponge, which in some cases has nearly eaten them away.

The carnivorous mollusca abound especially in Ireland,

occurring in hundreds where the ordinary phytophagous

species may be counted by individuals, the only exception

being the ordinary Turritella communis, which is a very common shell. It is singular that so few remains besides

shells occur in these deposits?as except many valves of

Balanus, a careful examination of hundreds of shells and

fragments produced only a few Polyzoa, Serpulae, and

others, barely a dozen examples in all.

In working out the fossils from Wexford, I have to

acknowledge with many thanks the assistance rendered me

by the Most Rev. William Codd, D.D., Lord Bishop of Ferns, and by the Rev. G. N. Harrison, M.A., of Ramsey, for the

gift and loans of specimens from the Blackwater cliffs

(Wexford) and the Cranstal or Shellag sands in the Isle of

Man.

Comparing the faunas of these widely separated areas, with those of all the other Pleistocene marine deposits in the

Irish Sea basin, older than the Estuarine Clays, including beds of various ages and origins, clay, gravels and sands from

1 Proc. Roy. Irish Acad.} Vol. xxx. (B), 1912. p. n.

As




Derry and the Point of Ayre southwards, and from West

Ireland to the midland English counties, and at all heights from the shore at Ballybrack to the Wicklow Mountains on

one side of the Irish Sea, and Moel Tryfaen, Gloppa and

other elevated sites of 1,200 or 1,400 feet on the other, it

will be seen at once that we are dealing with a very different

type of faunal life.

The recorded species from all the above deposits number

about 130, of which several are northern forms, including four or five not met with in the Wexford-Manx areas,

Cardium islandicum, Serxipes (Cardium) groenlandicus,

Rhynchonella psittacea, Turritella polaris, and Buccinum

groenlandicum. The southern species include Pect?n glaber

(Ballybrack), and twenty-five others not met with before

either in Wexford or in the Isle of Man.

Chiton marmoreus. Isocardia cor (Balbriggan). Bittium reticulatum. lLucinopsis undata.

Dentalium tarentinum. lMactra glauca. Nassa pygmaea. Modiolaria marmorata.

Rissoa membran?cea. Psammobia vespertina. Rissoa parva. Pholas candida.

Trochus cinerarius. Pholas parva. Trochus magus. Syndosmya alba.

Cardium aculeatum. Scrobicularia plana. Cardium exiguum. Tellina tenuis.

1Diplondonta rotundata. Tapes decussatus.

Lucina borealis. Venus gallina. Lucina divaricata.

Deducting the few exotic species mentioned above, the

fauna is a representative modern group of southern ten

dencies, entirely different from that of the Wexford-Manx

deposits. The causation of the latter group is still a matter of

question. If morainic, as photographs of the Blackwater

cliffs suggest, the question arises from whence did the

contained Pliocene fauna come, as there are no Pliocene

deposits known so far north till we come to Iceland, and

these are not Icelandic species, neither are there any traces

of them in the present Irish Sea floor.

Only recorded from Worsden, in Lancashire,



?9*$. Bell.?Fossil Shells from Wexford and Manxland. 113

If "

concentrated "

from the chocolate-coloured clay, this should contain a similar group of forms, which it

does not, or if it does, the evidence has never yet been

published, and the Pliocene species are referred by Messrs.

Cole and Hallissy to the gravels. The Blackwater cliffs extend nearly continuously for

twelve miles along the coast, with a thickness of 70 feet,

rising at the Head to 160 feet, made up of marls, sands and

gravels alternately disposed, with many small shell

fragments in the latter (Kinahan). Calcreted sands abound

here and in the Isle of Man. Their age being problematical and their origin equally so, I may be excused the suggestion that they are the relics of an early Irish sea or inlet

which originally started in early Pliocene times from

North Cornwall, and lasted till the tectonic changes, of

which we get such abundant evidence in Eastern

England, permitted the influx of northern waters, northern

shells, and floating ice-floes with their rock debris. Northern

shells began to arrive in England in the Upper or Boytonian

stage of the Coralline Crag, but the Northern Teilen (T.

balthica) did not appear till the very latest stage of the

Norfolk Icenian at Weybourn, and the presence of this shell

in the Wexford-Manx sea would imply that it was at this

stage the northern barrier was broken down in this direction.

I would suggest further that the shelly gravels at

Blackwater and other Wexford localities (and their sporadic occurrence is in favour of this conclusion) are current-swept sandbanks such as are recorded by Wyville Thomson off

the Portuguese coast1 where one haul of the dredge brought

up 113 species of shells alone. Of these 40 per cent, were

new to science, numerous Sicilian Tertiary forms and others

of northern types, besides many living Lusitanian species. The Turbot Bank, off the coast of Antrim, may be referred

to as another example of shelly sands and gravels. From

here and the immediate neighbourhood 246 species of

shells have been procured, mostly dead. It is doubtful

if any of these are in situ, certainly not such forms as Acirsa

borealis, Natica affinis, Trochus cinerarius, Trophon clath

ratus, Astyris rosacea, Buccinum cyaneum, or M oller?a

1 " The Depths of the Sea/' p. 183. 1879.




eostulata. For other examples of current-borne species see the Report, British Association, Leeds, 1890, page 415.

It is probably due to current action that so many shells of southern origin have found their way into the deeps off

S.W. Ireland, where Cassidaria rugosa, Ranella gigantea, and even Pedicularia sicula are found living with others of

purely northern type like Volumitra groenlandica. The term

" boulder-clay

" as commonly used is not

always appropriate, and I agree with Dr. Crosskey that it

should be confined to the inorganic "

till "

of land-ice origin, and not to the often fossiliferous clays of marine origin, whatever stones they may contain.

The substance called "

boulder-clay "

in maritime districts

is chiefly the sediment of the turbid streams pouring from the ice-front or face, or water-sorted material carried by floating ice. The late R. Brown1 noticed that such a stream

deposited a layer averaging three inches per annum over a

sea-bottom full of marine organisms and various stones, and remarks that such a deposit was indistinguishable from the usual so-called

" boulder-clay."

A very representative series of the Wexford shells has been forwarded to the National Museum, Dublin, and

nearly 100 examples of the Wexford-Manx mollusca have

been already figured by Mr. F. W. Harmer, M.A., F.G.S. in

his "Monograph of the Pliocene Mollusca" (Palaeontographi cal Society) of which the first volume has now been com

pleted.

Cringleford, Norwich.

1 Brown, R. : On the Physics of Arctic Ice. Quart. Jour. GeoL Soc,

xxvi , 1870, pp. 671-701.



fossil shells from wexford and manxland

Documents