58o 



G. K. GILBERT 



in situ. Ordinarily it is too steep for the horse, but is readily scaled 

 by the mountaineer. As a rule, the steeper slope either is constituted 

 by, or else includes, an abrupt cliff which at most points cannot be 

 climbed. Fig. i shows a group of high ridges in which the steeper 

 faces are turned to the north, and Fig. 2 a group in which they are 

 turned to the northeast. 



Fig. I. — Eastward from Mount Gardiner, Sierra Nevada. Compare the south- 

 ward (right) slopes with the north-facing cliffs. [Photograph by J. N. Le Conte.] 



These slopes are not controlled by rock structure. The principal 

 rock is granite, and this granite is in large part structureless. Where 

 it is traversed by joint systems the details of sculpture are greatly 

 influenced by the joints, but the trend and slope of the greater features 

 are independent of the joints. 



A little reflection shows that the distribution of steep slopes is 

 correlated with the alimentation of Pleistocene glaciers. The south- 

 ward slopes of the east-west ridges, because turned toward the sun, 

 lost more snow by melting and evaporation than did the northward 

 slopes, and a smaller fraction of the snowfall they received remained 



