422 



LAKE CHELAN 



glacier and a certain type of river. In the arid regions of the 

 West the streams which have their sources in the mountains 

 flow down into the valleys and disappear, heing absorbed by the 

 dry soil and the thirsty atmosphere. These streams, like glaciers, 

 bear detritus down from the mountains, and upon their disap- 

 pearance in the valley they drop this detritus as the glacier does. 

 There are, therefore, certain characteristics by which the gorge 

 produced by glacial erosion may be distinguished from that pro- 

 duced by aqueous erosion. The glacial gorge has the shape of 



CASCADE PASS AND AMPHITHEATER 



the capital letter U, while the waterworn gorge is a V-shaped 

 notch. In a glacial gorge the spurs separating the tributaries 

 have their ends blunted or planed off, while in a waterworn 

 gorge they are sharp and angular. In a glacial gorge the tribu- 

 taries enter the valle} r above its level, while in a waterworn 

 gorge they commonly grade down to its level. A glacial gorge 

 has an amphitheater at its head ; a waterworn gorge has not. 

 A glacial gorge is commonly lined near its lower end with lateral 

 moraines and across its foot stretches a terminal moraine, and 

 often this terminal moraine has formed a lake. 



