204 PKOCEEDIN'GS OP THE GEOLOGICAL SOCIETY. [Mar. 5, 



is an important point, in addition to previous knowledge, towards the 

 solution of the glacial theory ; for I do not see that these hollows 

 can in any way be accounted for by the hypothesis that they were 

 scooped by floating ice*. An iceberg that could float over the mar- 

 gin of a deep hollow would not touch the deeper recesses of the 

 bottom. I am therefore constrained to return, at least in part, to 

 the theory many years ago strongly advocated by Agassiz, that, in the 

 period of extremest cold of the Glacial epoch, great part of North 

 America, the north of the Continent ^of Europe, great part of Britain, 

 Ireland, and the "Western Isles t, were covered by sheets of true 

 glacier-ice in motion, which moulded the whole surface of the country, 

 and in favourable places scooped out depressions that subsequently 

 became lakes. 



This was effected by the great original glaciers (probably con- 

 nected with the origin of the unstratified boulder-clay) referred to in 

 my memoir on the glaciers of North Wales J, but the magnitude of 

 which I did not then sufficiently estimate. The cold, however, con- 

 tinued during the depression of North Wales and other districts 

 beneath the sea, when they received the stratified erratic drift ; and 

 glaciers not only did not cease at this time of depression, but were 

 again enlarged during the emergence of North Wales and other 

 countries, so as to plough the drift out of many valleys. These 

 enlarged glaciers, however, bore no comparison in size to the great 

 original sheets of ice that converted the North of Europe and 

 America into a country like North Greenland. The newer develop- 

 ment of glaciers was strictly local. Amelioration of climate had 

 already far advanced, and probably the gigantic glaciers of Old 

 Switzerland were shrinking into the mountain-valleys. 



Finally, if this be true, I find it difficult to believe that the change 

 of climate that put an end to this could be brought about by mere 

 changes of physical geography §. The change is too large and too 

 universal, having extended alike over the lowlands of the Northern 

 and the Southern Hemispheres. The shrunken or vanished ice of 

 mountain-ranges is indeed equally characteristic of the Himalaya, 

 the Lebanon, the Alps, the Scandinavian chain, the great chains of 

 North and South America, and of other minor ranges and clusters 

 of mountains like those of Britain and Ireland, the Black Forest, and 

 the Yosges. 



* I do not in any way wish to deny that much of the glaciation of the lower 

 countries that came within the limits of the Drift was effected by floating ice on 

 a large scale, which must have both polished and striated the rocks along which 

 it ground. I have, with other authors, described this in various memoirs. But 

 the two sets of phenomena are distinct. 



t The Lewes is covered by small lakes. 



I Quart. Journ. Geol. Soc. vol. xviii. p. 371. 



§ It has been suggested to me by Dr. Sibson that the prodigious waste of the 

 Alps by the gradual disintegration and diminution of the upper snow-fields, wit- 

 nessed by the great moraines of North Italy and other phenomena, must have 

 tended to lessen the glaciers. This is true, but, as he also believes, it is not of 

 itself enough to account for the shrinking of the ice into the higher valleys where 

 it is now alone found. 



