THE WORK OF THE ATMOSPHERE 



27 



the floor of a rock quarry, that it is similarly bowed up and broken. 

 Many bowlders which lie on the surface are seen to be "shelling off" 



Fig. 18. Crumbling on a mountain top. Kearsarge Pass, Sierra Nevada 

 Mountains. Changes of temperature one cause of the broken rock. 



(PI. IX, Fig. 1 p. 16), and the same thing is sometimes seen on moun- 

 tain tops (PL X, p. 1 7) . In high mountain regions where the changes 



Fig. 19. Talus at the foot of a peak in the Wasatch Range. 



of temperature of the rock are great and sudden, the exposed rock is 

 often much broken. So far has this rock-breaking gone, that the 



