HOW ROCK BECOMES SOIL 283 



into smaller and smaller particles. This same action of the 

 water also sorts the materials into the different sizes, and 

 one may find these sizes assorted in definite regions as he 

 passes from the shore into deep water. 



FIG. 138. A valley glacier 



A glacier on the slopes of Mount Rainier, Washington. At the lower end the ice is 

 covered by the broken stone which it is carrying. Photograph by Dr. G. E. Nichols 



284. Glaciers and the earth's crust. In former times gla- 

 ciers were important agencies in changing the earth's crust, 

 and in some places their work is still going on (fig. 138). 

 The glaciers have been formed by tremendous accumulations 

 of ice, which fell as snow and then, by pressure of its own 

 weight, became ice. Ice, like water, flows toward places of 

 lower level, though it flows very slowly. As it moves it may 



