THE WORK OF SNOW AND ICE 



255 



raphy of sufficient relief to offer some resistance, and yet too little 



to retard the progress of the ice seriously, will erode most effectively. 



Varied nature of glacial debris. From its mode of erosion it will 



be seen that a glacier may be charged with various sorts of material. 



Fig. 206. A mountain valley in the Wasatch Mountains, not glaciated. 

 (Photo, by Church.) 



At its bottom there may be (1) bowlders which the ice has picked 

 up from the surface, or which it has broken off from projecting 



Fig. 207. A mountain valley which has been strongly glaciated, Wasatch 

 Mountains. (Photo, by Church.) 



