300 THE EARTH'S SURFACE AND PLANT LIFE 



the material which the ice has scraped over it and borne 

 along. Here the soil that is left when the ice has retreated 

 is very thin. Such is much of the country of New England 

 and of eastern Canada. 



The valleys through which glaciers have gone are left 

 rounded out and shaped like a U. 



MARJELEN LAKE 



Glacial Lakes. The advancing or retreating ice may 

 happen to make a barrier to the escape of the drainage, 

 and thus may form a lake with an ice dam at one end. 

 The lake will continue to exist only so long as the ice ob- 

 structs the drainage. The Marjelen Lake in Switzerland 

 is a well-known example of this. 



Toward the close of the Glacial Period a vast lake of this 

 kind was formed in the northern part of the United States. 



