INTERGLACIAL EPOCHS. 289 



with a slower and more equable motion. As the ice-sheet ap- 

 proached its termination, more especially if that chanced to be 

 upon a broad and comparatively flat region, like East Anglia or 

 the plains of Northern Germany, the erosive power of the ice 

 would become weaker and weaker for two reasons : first, because 

 of its gradual attenuation, and secondly, because of its con- 

 stantly diminishing motion. These, in a few words, are the 

 varying effects which one might a priori infer would be most 

 likely to accompany the action of a great ice-sheet. And an 

 examination of the glacial phenomena of this and other countries 

 shows that the actual results are just as we might have antici- 

 pated, had it been previously revealed to us that a large part of 

 our hemisphere was, at a comparatively recent date, almost 

 entirely smothered in ice. In places where, from the nature of 

 the ground, we should look for traces of great glacial erosion, 

 we find rock-basins now occupied by lakes ; in broken hilly 

 tracts, where the ice-flow must have been comparatively rapid 

 but irregular, and the glaciation severe, we meet with roches 

 moutonne'es in abundance, but with very little boulder-clay • in 

 regions where the ice-flow has been opposed by cliffs and escarp- 

 ments, and where, therefore, the lateral pressure would be enor- 

 mous, the projecting rocks are either bevelled off and highly 

 abraded, or very much crushed, broken, confused, and displaced, 

 and their ruins commingled with the boulder-clay ; in open 

 lowlands and in broad valleys where, the ice -sheet would 

 advance with diminished but more equable motion, we come 

 upon widespread and often deep glacial deposits, and now and 

 again with interglacial beds ; while over regions where the 

 ice-sheet, gradually diminishing in thickness, crawled slowly to 

 its termination, we discover considerable accumulations of 

 boulder-clay, often resting upon apparently undisturbed beds 

 of gravel, sand, and clay. 



The distribution of interglacial deposits, therefore, is really 

 in itself a proof that they have been overridden by ice. When 

 they occur in highly glaciated regions, it is only as mere patches, 

 which, occupying sheltered places, have been preserved from 



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