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STUDIES, SCIENTIFIC AND SOCIAL 



that the ice-tool has done more than merely rub off the 

 angles and minor prominences, and that it has really ground 

 away rocky hills to an unknown but very considerable 

 extent ; and this conclusion is, as we shall see, supported 

 by a very large amount of confirmatory evidence. It may 

 be noted that ice-ground rocks usually show the direction 

 in which the ice has moved, by the side opposed to the 

 motion being more completely smoothed than the lee side, 

 which often retains some of its ruggedness, having been 

 protected partly by the ice overriding it and partly by 



Fig. 11. — ROCHES moutonnees, in idaho, u.s.a. 



the accumulation of its own debris. Where such rocks 

 occur in the higher parts of valleys the smooth side always 

 looks up the valley from which the glacier has descended. 

 In the more open parts of valleys, or in high coombs or 

 cirques, where two or more small ravines meet and where 

 the ice may have been embayed and have acquired a some- 

 what rotary motion, the rocks are seen to be ground down 

 on all sides into smooth mammillated mounds or hum- 

 mocks, showing that the ice has been forced into all the 

 irregularities of the surface. An example on a small scale 

 is to be seen in Cwm Glas, on the north side of Snowdon. 



