August i6, 1906J 



NATURE 



391 



.ind iheir ussociatwl jji-uvels to mark thrve mild inlpi- 

 Llliuial epochs ; and all except the first glaciation were sup- 

 posed to be represemed in the boulder-days of l,ancashiri' 

 and Cheshire.' Then, somewhat vaguely, it was allowed 

 that perhaps then- were only three separate fjlariations on 

 ihe cast coast, with a minor episode of recession of ihc 

 ice-margin ; and the Lancashire and Cheshire boulder-clays 

 were correlated with the two later of these glacial epochs." 

 Bm subseiiucntly wi- are reduced in the eastern district to 

 two epochs of glaciation, with one mild interval, of which 

 the equivalents aVe .ill recognised also in the north-west 

 of Kngland." 



While these and otlur similar changes may show a 

 laudable desire of their author to keep pace with ihi' 

 growth of definite information, 1 cannot help feeling that 

 they also show the premature character of the whole 

 scheme, and a flexibility in it that justifies suspicion. 

 Moreover, in spite of these frequent changes in the corre- 

 lation and this local lopping off of glacial and interglacial 

 episodes, we find, with surprise, that the number of 

 separate epochs in the classification has not diminishc-d, 

 but has actually increased, by regrowth in fresh places. 

 This, again, may betoken the inherent vitality of the 

 scheme, in which case it will gain strength from every 

 readjustment; but it must certainly also denote the weak- 

 ness of its original basis. In considering its application to 

 this country we will begin by glancing at the evidence for 

 the two earliest epochs of the classification. 



" .SVfliii.ni '• (/•'i>.v7 Glacial) and " Norfolhiaii " (First 

 Interglacial) Epochs. 



It is acknowledged that the First Glacial Kpoch is not 

 represented in Britain by any boulder-cl«y or other evidence 

 of land glaciation, but is based mainly upon the supposed 

 existence of a great Baltic glacier which overllowed the 

 southern part of the .Scandinavian peninsula from south- 

 east to north-west, a direction differing widely from that 

 of the later ice-sheets. This glaciation of Scania is sup- 

 posed to have been contemporaneous with the deposition 

 of the Chillesford Clay and Weybourn Crag of Norfolk, 

 which contain a marine fauna indicative of cold con- 

 ditions. The Forest Bed series of Norfolk, with its 

 temperate land fauna and flora, is then interpreted as the 

 product of a mild interglacial epoch (" Norfolkian ") inter- 

 calated between the " Scanian " glaciation and the more 

 severe " Siixonian " glaciation which followed ; and it is 

 implied that during this mild stage the earlier ice-shei-t 

 vanished. 



So far as 1 can gather, the recognition of the " Scanian " 

 ice-sheet rests on dubious grounds, being based chiefly on 

 the disputed supposition that the lower boulder-clay of 

 North Germany is not the equivalent of the lower boulder- 

 clay of Sweden, but of a subsequent Swedish boulder-clay. 

 l"'or the " Norfolkian " disappearance of the first Swedish 

 ice-sheet no direct evidence is forthcoming, since it is 

 acknowledged that no interglacial deposits representing 

 this stage have been found in Sweden. But the Norfolk 

 Forest Bed is here brought into the argument to prove the 

 '■ deglaciation " — so that the .Scandinavian geologist is 

 invited to accept the " First Interglacial Epoch " mainly 

 on the supposed strength of the British evidence, while 

 the British geologist is expected to acknowledge the " First 

 Glacial Epoch " on the supposed strength of the Swedish 

 evidence. This method of argument might have weight 

 if the evidence afforded bv either region w'ere perfectly 

 definite. But in the present instance the conclusion that 

 the Forest Bed represents an interglacial episode is not 

 acceptable to the observers who have the fullest knowledge 

 of the Norfolk sections, Mr. Clement Reid pointing out 

 that the enclosing of the North Sea by the union of Britain 

 with the southward continental land affords an adequate 

 explanation of the apparent clim;ilal discrepancv between 

 the fauna of the sea and that of land ' ; while Mr. I". W. 



1 " Great Ice Age," 2nd ed (1877), P- 393- 

 - " Prehistoric Eurf^pe " (i88r). pp. 26^-266. 



3 "Great Ice Age," 3rd. ed. (1894), chaps, xxv. and .v.vvi., and /™»«. 

 (;,vA (supra ci/.). 



■'The Pliocene Deposits of Brii.iin." .Ifcm. Ccft/. Strive}' (i&go), pp. 



190. 



NO. 1920, VOL. 74] 



llarmer shows the probability of the transport of southern 

 relics into this old estuarine deposit by river-drifting.' 



It has, indeed, been long recognised that the marine 

 Pliocene deposits of eastern England present us with an 

 intelligible chain of evidence for the gradual and un- 

 interrupted approach of the Glacial Period ; and to break 

 this chain will require stronger reasons than have yet been 

 adduced. From the Coralline Crag, with seas warmer 

 than at present, to the Red Crag and Norwich Crag, with 

 a northern element steadily g.iining ground in the fauna, 

 we pass upward to the Chillesford Clay and Weybourn 

 Crag, wherein this element becomes predominant. Then 

 follows the period of slight elevation indicated by the 

 Forest Bed, wherein, along with its lemperate-climato 

 fauna, such northern forms as the musk ox and glutton 

 are associated; and finally we gain just a glimpse of truly 

 arctic conditions in the I.eda tnyalis bed and the Arctic 

 freshwater bed, immediately before Ihe advent of the great 

 ice-sheet lh.it releiulessly blotted out both land and sea. 



•' Saxonian ■' iSccoml Chunil). •• Ifclvclian" (Second 

 Interglacial), and " I'olandian " (77n></ Glacial) Epochs. 



Regarding the glacial severity of the ensuing stage — the 

 " Sa.xonian Epoch " of Prof. Gcikie's schemi — all are 

 agreed ; and from this stage onward to the close of the 

 " (ilacial Period " as usually understood, or to the close of 

 the " Polandian Epoch " of the proposed classification, our 

 dillicuUies of interpretation arise not from lack of evidence, 

 but rather from its superabundance and local intricacies. 



It happens, fortunately, that the great bulk of our 

 British drifts, with the exception only of those in certain 

 mountainous districts, arc now included by Prof. Geikic 

 within the two above-mentjoned glacial epochs and the 

 intervening "Helvetian Interglacial Epoch." Therefore, 

 in dealing more particularly with the deposits assigned to 

 these three epochs in certain typically glaciated districts, 

 we shall bring under consideration a considerable portion 

 of the drifts of our islands, and shall obtain results which 

 can be applied to many other areas in which the structure 

 of the glacial deposits is essentially similar. The first 

 district to be considered shall be that which lies nearest 

 us ; and in discussing the drifts of East Yorkshire I pro- 

 pose to interweave some personal opinions that I have 

 deduced from the facts, which will afterwards be given 

 wider application. 



E.\ST Vorkshirf; nuiits. — The long cliff-sections between 

 the Humber and the Tees constitute one of the best ex- 

 posures of lowland drifts in Britain, or even in Europe. 

 They fortunately include some deposits which reveal the 

 conditions prevailing in the neighbouring part of the North 

 Sea basin just before the great glaciation ; and they there- 

 fore enable us without interruption to continue the history 

 begun in East Anglia. 



The old cliff of chalk and the marine beach at its foot 

 which lie buried at Sewerby, on the southern side of Flain- 

 borough Head, under sheets of boulder-clay and gravel, 

 prove to us that at the very beginning of glacial times the 

 North Sea still held possession of its basin, and with a 

 surprisingly slight difference from its present level. .\ 

 few far-transported stones in the old beach denote that 

 ice-floes sometimes drifted southward into Holderness Bay ; 

 while the bones of animals in the shingle, and in the 

 blown sand which overlies it, prove that among the 

 denizens of the neighbouring land were the elephant 

 (E. aniiquns), rhinoceros (Ti'. lepiorhinus), hippopotamus 

 (//. amphibius), and bison. This fauna is frequently con- 

 sidered to be proof of mild conditions of climate ; but from 

 the mode of its occurrence in this and other places, I can 

 find no reason to doubt that these animals inhabited the 

 country, perhaps as seasonal migrants, until the time that 

 it was actually covered by the encroaching ice-sheets. 



.'Vnd here I may note my opinion, that throughout the 

 discussion of our glacial deposits too much weight has been 

 allowed to the deductions regarding climate based upon 

 scanty indications afforded by the ancient fauna and flora. 



I "The Later Tertiary History of East Ang 

 vol. xvii. (1902V p. 449. 



r,vr. Ctol. As 



