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PHYSICAL GEOLOGY 



brought up in other ways from the bottom. Belts of sur- 

 face debris on the sides of valley glaciers are called lateral 

 moraines (Figs. 220 and 221). If valley glaciers melt away, 

 their surface lateral moraines are deposited on the valley 

 floor beneath, along with material left by the bottom ice 

 which moved from the center to the sides of the glacier 

 (p. 198). In most cases the latter material makes up much 



FIG. 221. The Corner Glacier with its feeders the Grenz, Schwarze, 

 Breithorn, and Theodule Glaciers. Shows lateral and medial moraines, 

 and the sources of the morainic debris. (R. T. Chamberlin.) 



the larger part of the deposits. Lines of surface debris in 

 or near the center are medial moraines (Fig. 221). In many 

 cases medial moraines are the result of the union of two 

 valley glaciers, whose adjacent lateral moraines have joined 

 and occupy a medial position on the main glacier. Debris 

 on the surface of a glacier near its head may be buried by 

 accumulations of snow and carried forward in the body of 

 the ice. Surface material may also work its way through 



