GLACIERS 223 



tures described above occur in western United States and Can- 

 ada, among the Alps, and elsewhere, in many valleys now ice- 

 free. They have been more or less modified, however, since 



FIG. 237. Near view of the walls of a cirque. 



the disappearance of the glaciers, and will ultimately be de- 

 stroyed. The glaciated rock surfaces not covered with drift 

 are being weathered. The steep sides and heads of the val- 

 leys favor landslides, the accumulation of talus, and the 

 formation of alluvial cones. The streams are grading the of- 

 ten irregular beds of the former glaciers, lowering the hanging 

 valleys, and filling or draining the lakes. The relative extent 

 of these changes in different valleys is a rough measure of the 



