GLACIAL FORMATIONS 377 



as rivers do when overloaded. When the glaciers retreat, 

 ice walls which bordered the channels melt away, and the 

 sand and gravel which the streams had laid down along 

 their beds are left as long, irregular ridges, at the end of 

 which sometimes an alluvial fan or delta may be found. 

 Such long ridges are called eskers. 



GLACIAL ROCK LAKE. 



Where the glacier has little load, as near its source, the 

 bed rock is stripped bare, smoothed, polished, and 

 scratched by the material which the ice has scraped over 

 it and borne away. Where the rock is soft, it is scooped 

 out, and hollows are formed, afterward making lakes ; 

 and where it is hard, rounded ridges are made. 



The valleys through which glaciers go are rounded 

 out and left shaped like a U. If side glaciers join the main 

 glacier, they may not be able to wear down their valleys 

 as fast as the main glacier, so the mouths of these U-shaped 



