280 R. Chambers, Esq., on Glacial Phenomena 



merged ; those parts which remained above the waves were 

 the residence of the large mammalia, while under the waters 

 there took place deposits of plastic clay, washed off from the 

 boulder clay, alternating with beds of sand, of which the 

 materials were obtained from the hills. 



Next succeeded a new cold period, in which the masses of 

 the land produced glaciers descending with their subaerial 

 detritus into the sea, as we see at this day in Spitzbergen. 

 Borne along in determinate directions by currents, the ice- 

 borne detritus was strewed along the sea-bottom, so as to 

 form the till of Scotland, the drift of England, and the cor- 

 responding deposits of Northern Europe and America. 



This also passed away, giving place to renewed deposits 

 of sand and gravel under an ordinary sea. 



Then was a period of larger extent of dry land, — larger, 

 even, than what now exists. Districts now little above the 

 level of the sea, and some a little below it, were then so far 

 elevated as to be subjected to a comparatively severe tem- 

 perature. What are now low grounds in Hampshire, bore 

 the coniferse and other trees now proper to the Scottish hills. 

 Snowdonia, the Lake Country, Assynt, the Cuchullin Hills, 

 and other districts in Scotland, were the seats of glaciers 

 like those now existing in the Alps, by which the detritus of 

 an earlier cold period were swept out of the valleys forming 

 their beds. 



Then came another deep submergence, attended still by 

 great cold. Masses of ice floating away from the insulated 

 hills, bore off large blocks in the direction of the prevalent 

 currents, and thus the Criffel granite became strewed in Cum- 

 berland, and the Shap granite was transported to the plains 

 of Salop and the vale of York. 



The emergence consequent upon this state of things, still 

 attended by a low temperature and a transportation of erra- 

 tics, was by stages, to which must be attributed the ancient 

 beaches now traceable over the face of the country. 



Perhaps the most valuable effect of the facts here adduced 

 is in the light which they throw upon the great, but hitherto 

 mysterious processes of denudation and the formation of val- 

 leys. To suppose water capable of cutting out all the wide 



