298 W. J. Miller — Ice Movement and Erosion. 



erosive agent as claimed by some geologists. The conclusion 

 seems to be that the only considerable ice erosion was along 

 the eastern side of Tug Hill and the valley eastward, where the 

 ice caused channel-straightening accompanied by some deepen- 

 ing. The very soft shales were considerably cut away ; the 

 harder limestones were less affected ; while the very hard Pre- 

 cambrians yielded least. Gilbert* in speaking of ice erosion in 

 western New York, near Lock port, says : " The district exhibits 

 a marked contrast between the extent of erosion from a broad 

 mass of limestone on the one hand and a broad mass of shale on 

 the other, the ratio being, roughly, as 1 to 10 or 1 to 20 ." 

 Thus in the Black river valley we also have a good example 

 of differential ice erosion. 



Hamilton College, Clinton, New York. 

 January, 1909. 



*Bull. Geol. Soc. Amer., vol. x, p. 180, 1899. 



