THE GREAT RELIEF FEATURES OF THE LAND 283 



of weathering arc removed promptly. 

 The higher slopes of many moun- 

 tains are accordingly of bare rock 

 (Fig. 298). Daily changes in the 

 temperature of the rocks are greater 

 in the high altitudes of lofty moun- 

 tains than in lower situations. Rock 

 splitting is therefore important, and 

 where the slopes are not too steep, 

 mountains may be covered with 

 loose, angular fragments broken from 

 the rocks beneath (Figs. 299 and 

 95). Mountains receive greater 

 rainfall than plains, and even in 

 arid regions their steep valleys may 

 contain rushing torrents. Rapid cutting is sometimes op- 

 posed, however, by the fact that the streams are clear 

 (Why?). The absence of protecting vegetation on many 

 upper mountain slopes is important (How?). Wind veloci- 

 ties are often great about mountain heights, but generally 



FIG. 298. Summit of Mt. 

 Whitney, Cal. (Fairbanks.) 



FIG. 299. Crumbling on a peak in the Bighorn Mountains, Wyo. 



bridge.) 



(Trow- 



