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IV.—On Changes of Climate during the Glacial Epoch

Published online by Cambridge University Press:  01 May 2009

James Geikie
James Geikie
Affiliation:
District Surveyor of the Geological Survey of Scotland
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Extract

If one were asked to put into a few words the general results which have been arrived at from a study of the Glacial deposits, he would probably say that these deposits gave evidence of a severe Arctic condition of things having obtained in this country,—that the gradual approach of this Arctic climate caused the disappearance from our area of the fauna and flora which had previously characterized it,—that during the continuance of the cold in Britain several speciesof mammalia appear to have died out in the more southern regions of Europe, whither they had migrated,—and that it was not until after our climate had become greatly ameliorated that these islands were visited by what are termed the “Post-glacial mammalia,” several species of which, however, had been denizens. of Britain and northern Europe inPre-glacial times. In short, our island, throughout the Glacial period proper, is commonly supposed to have remained a barren waste of snow and ice. But the evidence which has been accumulating during recent years will compel us, I believe, to modify materially these general inferences. So far from the Glacial epoch having been one long continuous age of ice, it would appear to have been broken up by many intervening periods of less Arctic, and even temperate conditions, during whichthe snow and ice disappeared from our low grounds, and the glaciers shrunk back into our mountain valleys. I speak, of course, of that portion of the Glacial epoch which was antecedent to the general submergence, and is represented by the Till or Boulder-clay of Scotland. la this short paper I propose to give an outline of the facts upon which these conclusions are based. But before doing so it may be well to point out the order of succession of the Scottish drift deposits, which is now no longer a matter of dispute. Beginning with the lower beds, we have the following sequence

Type
Original Articles
Information
Geological Magazine , Volume 8 , Issue 90 , December 1871 , pp. 545 - 553
Copyright
Copyright © Cambridge University Press 1871

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References

page 545 note 1 Under this head I include those unstratified, more or less tenacious deposits of clay, which are so abundantly charged with well-polished and striated stones. They are all clearly of older date than the Kame and brick-clay series. I thought at onetime that the less tenacious Till-beds might possibly be of later date than the tougher and harder stony clays: but subsequent investigation has shown that such is not the case. The character of the Till depends in large measure upon the nature of the rocks to the demolition of which it owes its origin; and also in some degree to the pressure of the ice under which it was formed. There is a coarse moraine-like accumulation of earthy clay full of rough unpolished angular blocks and debris, but with only a few scratched stones, which has sometimes been called Boulder-clay. But this deposit is clearly posterior in date to the true Till, and belongs to the upper drift series. Again, some of our later glacial brick-clays contain scattered stones, many of which are striated. These clays, if met with in the more southerly districts of England, would probably be called Boulder-clays: in Scotland they are all of marine origin.

page 547 note 1 This was on the top of Allermuir Hill. The clay contained fragments of mica-schist and several other rocks, none of which belonged to the hill itself.

page 551 note 1 Vol. V. p. 393.

page 553 note 1 Descriptions of inter-Glacial deposits will be found in “Glacial Drift of Scotland,” by Geikie, A., Glasgow Geol. Soc., vol. i., part ii.Google Scholar; “On the Surface Geology of the District round Glasgow,” by Bennie, James, Glasgow Geol. Soc., vol. iii., part i.Google Scholar; “On Two River Channels buried under Drift,” etc., by Croll, James, Edinburgh Geol. Soc., vol. i., part iii.Google Scholar; “On the Discovery of a Sand Dyke,” etc., by Dick, Robert, Edinburgh Geol. Soc., vol. i. part. iii.Google Scholar; Explanation of Sheet 24, Geol. Survey of Scotland, etc., etc.Google Scholar