596 



NATURE 



[August i6, 1906 



points to a shifting westward of the area of greatest 

 precipitation. 



Owing to its peripheral position, the Cortc district seems 

 to liave been set free from ils ice-mantle much earlier 

 than the more northerly parts of Ireland ; and if there had 

 been marine submergence later than the period of maxi- 

 mum glaciation, it should have left clear traces in this 

 area. But we found, instead, that all the deposits newer 

 than the boulder-clay were unmistakably of fluviatile or 

 sub-aerial origin, and occupied positions that they 

 could not have maintained if any submergence had 

 occurred. 



Dublin District. — In the Dublin district the lower shelly 

 boulder-clay was carried for some distance inland during 

 an early stage in the glaciation, but afterwards there was 

 a great outpouring of the Ivernian ice from west-north- 

 west round the northern flank of the Dublin Mountains. 

 As the Pennine ice was deflected southward on reaching 

 the North Sea Basin, so was this Ivernian ice deflected 

 southward parallel to the coast in the Irish Sea Basin, 

 the persistence of ice-lobes within the basins being the 

 only adequate explanation in both cases. 



The shelly gravels associated with the Dublin drifts are 

 of peculiar interest, since they occur at heights ranging 

 up to 1200 feet above sea-level, and are typical of the other 

 high-level shelly drifts of the " West British " basin, 

 including the much-discussed deposits of Moel Tryfaen and 

 Macclesfield. The position of these gravels on the flanks 

 of the Dublin Mountains at the margin of the heavily 

 drift-covered country, their moundy outlines, sporadic 

 development, disregard for contours, character of the fauna, 

 relationship to the boulder-clay, and, in fact, every feature 

 they possess, tell against the possibility of these gravels 

 being of marine origin or other than the marginal de- 

 posits of the ice-sheet. Gravels at much low-er levels in 

 the same district that are associated with the ice-flow 

 from the interior of the country contain no shell frag- 

 ments. 



The fine coast sections between Killiney and Bray show 

 the usual features of a lower shelly boulder-clay brought 

 in obliquely from the seaward and an upper boulder-clay 

 derived from the landward ice : and they show, too, that 

 the so-called " middle glacial " gravels are merely local 

 modifications of the glacial series, interwoven with the 

 boulder-clays and of contemporaneous accumulation. In 

 this district there is again strong evidence that the land 

 remained above sea-level during the final waning of the 

 ice, and that it has not since undergone any submergence, 

 except to a depth of not more than lo feet above present 

 sea-level. 



Belfast District. — In the country around Belfast the 

 glacial phenomena presented the same general features. 

 The principal constituents were again — a shelly boulder- 

 clay, brought in from the northward, interlocked in a few 

 places w-ith moundy gravels, also containing a few shell 

 fragments ; and a contemporaneous drift in the hillv 

 interior of more immediately local origin, associated 

 with gravels of like composition and without any marine 

 relics. 



The only new feature was the presence of a mass of 

 unfossiliferous sand and laminated clay in the recess at the 

 head of Belfast Lough, which appears to have been de- 

 posited in a glaciallv dammed lake during the waning phase 

 of the glaciation. This deposit is in places interbedded with 

 and partly overlain by boulder-clay. Its relation to the 

 surrounding drifts seems only explicable under the suppo- 

 sition that the oscillating margin of the ice-lobe was con- 

 tinuously present in the vicinity ; and nowhere in the 

 district did we find any evidence to suggest that there were 

 epochs of glaciation separated by warm interglacial 

 episodes. 



The conditions in this district subsequent to the dis- 

 appearance of the ice-sheets are recorded in the post-glacial 

 deposits at the head of Belfast Lough, which have been 

 carefully investigated by Mr. R. Lloyd Praeger.' A bed 

 nf peat, passing considerably below sea-level, proves that 

 at first the land stood higher than at present, while the 



1 " Report on the Estuarlne Clav; of the North-east of Ireland.' P,v. 

 Roy. Irish .4cacl (3), vn\. u. (1892), pp =11-289. 



NO. 1920, VOL. 74] 



estuarine clays which overlie this peat demonstrate a more 

 recent submergence to a depth of not more than 15 or 20 

 feet above present sea-level. This degree of submergence 

 is marked also by the raised beach which almost every- 

 where fringes the north-eastern coast of Ireland, and there 

 is no adequate evidence for any other epoch of submergence 

 in Ireland between the beginning of the Glacial Period 

 and the present time. 



Limerick District. — In the country around Limerick we 

 had to deal with the products of the Ivernian sheet-ice 

 only, uncomplicated by exterior invasion ; and here not 

 even the staunchest supporter of Interglacial deglaciation 

 and submergence could have found a basis for his hypo- 

 thesis. Although the drifts occur thickly on low ground 

 falling to sea-level, as well as on the hills, and although 

 they include numerous eskers and broad fans of sand and 

 gravel, not a single shell fragment has been discovered in 

 them, nor any other indication of marine agency. On the 

 other hand, there is abundant evidence that the boulder- 

 clay and the stratified drift were formed contemporaneously, 

 the one by the ice-sheet itself, and the other by the flood- 

 waters in and around it. Another noteworthv point in 

 this district is that, in spite of its proximity to the west 

 coast, with the broad estuary of the Shannon offering at 

 present an open passage thereto, the general movement 

 of the land-ice was south-eastward across the low ground, 

 trending inland, and not toward the coast. It appears, 

 therefore, that the ice-sheet at the mouth of the Shannon 

 was sufficiently thick to dominate that of the country 

 to the east in this part of Ireland. Farther to the 

 northward, however, and also to the southward, it is 

 known that ice-lobes passed outward toward the 

 Atlantic. 



I think that this review of the testimony from the areas 

 which I have closely investigated will serve to show how 

 extraordinarily elusive is the evidence for even the prin- 

 cipal Interglacial epoch of the proposed scheme. I shall 

 venture to claim that in each of these areas all the avail- 

 able data concerning the superficial deposits were system- 

 atically examined in the field and conscientiously sifted, 

 without prejudice towards one opinion or another. Yet 

 the only support which has been found for the Interglacial 

 hypothesis is from a single section in North Lincolnshire, 

 and although in this case the facts give some encourage- 

 ment to the idea, they can be as readily explained without 

 recourse to it. 



In view of some evidence which we have still to consider, 

 it is especially remarkable that in the range of magnificent 

 coast sections, not of these areas alone, but of the whole 

 of our islands, there is not, so far as I am aware, a single 

 known occurrence of fossiliferous land deposits, peaty or 

 otherwise, interbedded with boulder-clavs ; and we have, 

 therefore, to depend entirely upon much less satisfactory 

 exposures in the interior of the country for evidence of 

 this kind.' 



After the experience above recorded, it is inevitable that 

 I shall approach the remainder of the British evidence for 

 the Interglacial hypothesis in sceptical mood, though, I 

 hope, without dogmatism. In discussing this evidence from 

 districts of which my personal knowledge is scanty, or 

 altogether wanting, I shall perforce have to depend mainlv 

 upon the literature of the subject, although I am fully 

 aware that of the opinionative churning of this literature 

 there has already been more than enough. 



East Anglia. — In East Anglia, the original opinion that 

 the shellv " middle glacial " sands and gravels represent 

 a mild interglacial epoch of submergence is no longer 

 prevalent. Mr. F. W. Harmer^ points out that both the 

 mollusca and ostracoda they contain are generally of a 

 boreal or arctic character; and my colleague, Mr. H. B. 

 Woodward, after extensive field-experience of these deposits, 

 concludes that they are inseparable from the associated 



1 I diH. indi-ed. at one time th!nl< that I had discovered an anrient <oiI 

 with land shells between two boulder-clays in the cliffs '.of Filev Bay. hut 

 after murh examination T found that it was a recent soil, covered by a hu^e 

 slip of boulder-clav from the upper part of the cliff and then exposed in 

 fection bv the cutting back of the coast. 



- "The r.ater Tertiary History of East Anglia," Pi-oc. Cenl. Assoc, 

 vol. xvli (iQo2\ rp. 4sS~462 ; ond "Pleistocene Deposits of East AnRlia.' 

 Pros. YorksGcol. and rolrttrh .SVc, vol. xv. (1004!, p, 322. 



