EROSION BY GLACIERS 



149 



Fig. 14'). Stria.-, grooves, etc., in a canyon tributary to Big Cottonwood Can- 

 yon. Wasatcfa Mountains. (Church.) 



\ 



Fig. 147. Stones striated by glacial wear. Their shapes, as well as their mark- 

 ings, are characteristic. 



decrease of motion, 1 and decrease of motion retards erosion. When 

 any considerable thickness of ice at the bottom of a glacier is full 

 of debris, the loaded part may approach stagnancy, while the 

 cleaner ice above shears over it. A moderate but not excessive load 

 of debris, therefore, favors great erosion. Something depends, too, 

 on the character of the load. Coarse, hard, and angular debris is 

 1 Russell. Jour, of Geol., Vol. Ill, p. 823. 



