August i6, 1906] 



NATURE 



395 



llc■p(l^its in the N'ale of Eden,' and his loncUisions have 

 been supported by the researches of Dr. N. O. Hoist in 

 Southern Greenland, where there was found to be the same 

 difference between the unoxidised ground-moraine and the 

 overlying oxidised material o( " englacial " origin as 

 between the lower and upper boulder-days in areas of 

 ancient glaciation." in adopting this explanation we must 

 recognise that the uppermost boulder-day of an extensive 

 area was not formed at exactly the same time in every 

 pan, but was accumulated progressively as a margiiial 

 residue during the emergence of the land from its icy 

 cloak. 



/.iWc Glacial and I'nsl.Glacial Dcposils.—Oi the glacial 

 and interglacial epochs of Prof. C.eiUie's scheme later than 

 thr " Polandian " it is admitted that no indication has 

 been found in Yorkshire. There seems, on the contrary, 

 to be evidence of steady amelioration in the climate, as 

 the glacial deposits opposite the mouths of the Wold valleys 

 ari! overlain, first by great deltas of chalky gravel, denoting 

 torrential floods, probably from the seasonal melting of 

 heavy snows ; and then, in the hollows of these gravels. 

 vr of the boulder-day itself, we find freshwater marl and 

 pe.it that were deposited in the many lakelets and marshes 

 that dotted the Holderness plain ; and in the lower layers 

 of certain of these freshwater deposits the leaves of the 

 arctic birch (lietula nana) have been delected,'' indicating 

 a climate colder than at present. 



In East Yorkshire, then, w'e appear to have a continuous 

 record of the events from the beginning to the end of the 

 Glacial Period ; and yet, if I read the sections aright, we 

 Van find no place iiiio which a single mild interglacial 

 epoch can be intercalated. 



Let us now more briefly consider certain glaciated areas 

 within til..- inlluence of the " \^'cst British " ice-lobe which 

 ! h.ive p.M-son.illv investigated. 



nidi-T.s OF TttE Isle or M.is. — Erom its isolated position 

 in the midst of the Irish Sea, the Isle of Man constitutes 

 an e.xcellent gauge or glacionieter, on which is recorded 

 the course of events within the basin occupied by the West 

 British ice-lobe. In carrying out the geological survey of 

 this island I made a close examination of its glacial de- 

 posits in every part, and have stated the results rather fully 

 in a recently published memoir.'' 



We find here, as in Yorkshire, that prior to the glaci- 

 ation there was a sea-niargin at approximately its present 

 level and, where the coast is composed of " solid " rocks, 

 in approximately its present position. In this sea, marine 

 deposits indicative of cold conditions were accumulated, 

 and were afterwards displaced and mingled with the 

 boulder-day of an ice-sheet that gradually filled the basin 

 and swept southward, or south-south-eastward, over the 

 very summit of the island. At its maximum the surface 

 of this ice-sheet stood more than 2000 feet higher than 

 present sea-level. The difference between the altitude 

 attained by this ice and that of the East British lobe in 

 the same latitude is especially noteworthy. In Yorkshire 

 t!ie eitstern ice did not reach much above Soo feet on the 

 Hanks of the Cleveland Hills, declining to 500 feet or 

 under off Flaniborough Head. The higher land which 

 surrounds the Irish Sea Basin may be in part responsible 

 for this difference, but I think that it must have been 

 m.iinly due to the heavier precipitation in the west. 



Then followed a declining stage in the glaciation, during 

 which the ice-sheet shrank away from the hills, which 

 were never again covered. Ow-ing to local circumstances 

 that are readily recognisable, the recession of its margin 

 was relatively accelerated in the northern part of the 

 island, so that a broad hollow was formed there between 



pp. 



! Work in Edenside 

 167. 



Tr. 



'i:. L I 



y/„mf Assoc, no. i2(i3S6 7), 



' Dr. N. O. HoUts Studies in Glacial Geology." by Dr. J. LindaVil, 

 A>iiL>ii'an Naturalist. Aug. 18S8. pp. 70';-7i2. It should be noted, how- 

 ever, that Prof. R. D. Salisbury did not find this difference apparent in the 

 moraines of North Greenland glaciers. See fonrn. Ct-oi., vol. iv. (1896), 

 pp. S06-7. 



" Bv Dr. A. G. Nathorst. at Bridlington ; and by C. Reid, at Holmpion. 

 " Geology of Holderness, ' pp 78 and 8i. 



•■ "The Geology sf the Isle of Man " (1903). .I/.-/;/. (Uol. Siii-.-o: 



NO. I 920, VOL. 74] 



the hills and the ice-border; and in this hollow a mass of 

 stratified drift was deposited. From its terraced aspect 

 and the occurrence of scattered shells, I thought at first 

 that this deposit might be of marine origin ; but examin- 

 ation in detail convinced me, as it had previously convinced 

 Prof. P. E. Kendall,' that the phenomena could only be 

 explained by regarding the stratified material as marginal 

 •' overwash " from ihe ice-front. .Xs in Yorkshire, the 

 association of the boulder-clays with the stratified drift is 

 in most places so intimate that again the evidence for the 

 continuous presence of the ice-sheet in the surrounding 

 basin seems irrefragable. 



Following closely upon this local deposition of stratified 

 drift, there appears to have been a limited readvance of 

 the ice, which brought about the accumulation of an upper 

 boulder-clay on parts of the low ground. But, unlike the 

 Lpper Clay of Yorkshire, this bed lies well within the 

 limits of the lower clays, both in extent and elevation ; and 

 it seems to denote only a slight augmentation of the 

 persisting ice-sheet, which was thus enabled to close in 

 again upon the lower flanks of the hills. 



The end of the glacial invasion was marked by similar 

 conditions to those found in Holderness. Great fans of 

 llood-gravel were spread out around the mouths of the 

 upland glens ; and the hollows in the drift-plain were 

 occupied by lakelets, now mostly obliterated by an in- 

 filling of rnarly and peaty sediments. .-Kniong the plants 

 found in a bed' near the base of one of these hollows is a 

 northern willow [Salix herbacca), along with the remains 

 of a minute arctic freshwater crustacean {I.cpidtirus 

 glacialis) ; and similar remains were also found in a peaty 

 iaver inlerbedded with the flood-gravels. 



Here, then, is another area in which the drifts are fully 

 developed and magnificently exposed in cliff sections, but 

 still yield no proof of the supposed interglacial epochs or 

 of the n-arine subinergence. 



Irish Drifts. — During recent years, while attached to 

 the staff of the Geological Survey in Ireland, I had occasion 

 systematically to examine the drifts of four separate and 

 typical areas. With my colleagues of the Irish staff, the 

 mapping of the superficial deposits was carried out in the 

 country around the cities of Dublin, Belfast, Cork, and 

 Limerick. The results, which have been fully stated in 

 recent publications of the Survey, = differ only in detail 

 from those already dealt with, and need not detain us 

 long. 



Cork District. — In the south of Ireland, the infra-glacial 

 beach, with its associated cliff and shore-line, discovered 

 bv Messrs. H. B. Muff and W. B. Wright,^ is essentially 

 similar to the buried cliff at Sewerby and at almost exactly 

 the same level. The presence of the old beach-line within 

 the submerged valleys or rias of this coast proves that the 

 valleys were excavated during some earlier stage of eleva- 

 tion.' In its eastward extension the beach, with its cover- 

 ing of sub-aiirial land-waste or " head," is overlain by the 

 shelly boulder-clay of the West British ice-lobe ; but in the 

 south-west of Ireland, where the glaciation was from land- 

 ward, this boulder-clav is absent, and its place is taken 

 bv a till of more local origin. The Cork district appears 

 tej have lain not far within the southerly bounds of the 

 ice-sheets, and its valleys were filled to the brim almost 

 entirely with ice from the interior of Ireland. Where the 

 products of this ice are seen in contact with the shelly 

 drift, as in the vicinity of Youghal, the latter lies under- 

 most ; but the evidence implies that the two ice-sheets were 

 coexistent, and there is no indication of any break in the 

 glaciation.^ Both here and in the Dublin district there 

 appears to have been a shrinkage in the West British lobe 

 while the Ivernian ice was still advancing, which again 



1 "On the Glacial Geology of the Isle of Man. )ii Li,' 

 vol. i. pt. t2. pp 107-438. 



■i Menis. Geol. Sur-,'ev : " The Ge.i'ogy of the Country J 

 (roo3): "The Geology of the Country around Belfast ' 

 Geology of the Coumry around Cork and Cork Harbour' 

 Geology of the Country around Limerick' (in press). 



^ Wright and Muff, "The Pre-alacial Raised Beach of th. 

 of Ireland." Sc. Proc. Roy. DuMin So,.. N.S., vol. .\. 

 pp. 



ound Dublin " 

 (rgo4); "The 

 (rgos): "The 



South Coa-t 

 pt. ir (1904), 



