DRUMLWS. 295 



would often be comparatively rapid, but very irregular — 

 lagging here, flowing quickly there — while in wide, open 

 valleys that sloped gently to the sea, such, for example, as 

 those of the Forth and the Tweed, the whole body of the ice 

 would flow with a slower and more equable motion. As the 

 ice-sheet approached its termination, more especially if that 

 terminus chanced to be upon a broad and comparatively flat 

 region, like East Anglia, 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 coun- 

 tries shows that the actual results are just as we might have 

 anticipated, 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 ; in broken, hilly tracts, where the 

 ice-flow must have been comparatively rapid but irregular, and 

 the glaciation severe, we meet with roclies moutonnees in abun- 

 dance, but with very little till ; in the open Lowlands and in the 

 broad valleys where the ice-sheet would advance with dimin- 

 ished but more equable motion, we come upon wide-spread and 

 often deep glacial deposits, and now and again with interglacial 

 beds ; while over regions where the gradually decreasing ice- 

 sheet crawled slowly to its termination, we discover consider- 

 able accumulations of till, often resting upon apparently un- 

 disturbed beds of gravel, sand, and clay. 



Tlie 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 pre- 

 served from utter destruction. In the opener, low grounds 

 they are found in greater force, although in such places they 

 almost invariably afford more or less strong evidence of having 

 been subjected to much erosion and crumpling. But the far- 

 ther we recede from the principal centers of glaciation, and the 



