202 ELEMENTARY GEOLOGY 
Plate 10). In this is transported some of the rock 
material which the glacier was carrying. 
Valley glaciers differ very much in their features, 
particularly in their width, depth, and length. There 
is much difference according to the supply of snow, the 
slope of the valley, and also its width. The glaciers of 
Fie. 106. 
An ice-fall in one of the Swiss glaciers. 
the Alps (Plate 10) are often five miles long, while the 
Aletsch is ten miles in length, over a mile wide, and 
more than one thousand feet in depth. Many of 
the Alaskan glaciers are much larger and grander than 
those of the Alps. 
As the ice moves over its rock bed, it sometimes 
encounters a steep descent, and then the glacier sur- 
face becomes broken and irregular, forming an ice-fall 
