THE WORK OF THE ATMOSPHERE 



101 



temperature. Under the heat of day the more rapidly ex- 

 panding surface accordingly becomes too large to fit the interior, 

 and with the fall of temperature in late afternoon and night 



FIG. 94. Exfoliate weathering in granite. Alabama Hills, Owens Valley, 

 Cal. (Trowbridge.) 



the surface layer becomes too small for the less rapidly shrink- 

 ing rock beneath. As a consequence, the surfaces of rocks often 

 shell off (Figs. 93 and 94), the process being known as exfolia- 



FIG. 95. Summit of Pikes Peak, Colorado, showing broken character of 



the rock. (R. T. Chamberlin.) 

 B. & B. GEOL. 7 



