274 



THE EARTH'S CRUST 



INDIAN HIEROGLYPHICS CUT ON THE 

 STEEP WALL OF A MESA 



sissippi River the open 

 prairies of the north and 

 the coastal plain of the 

 south gradually merge 

 into a broad extent of 

 territory that slopes up- 

 ward until it meets the 

 eastern Rocky Mountain 

 plateau five or six thou- 

 sand feet above sea 

 level. The slope of this 

 area is so gradual that 

 the change of elevation 

 is hardly noticeable, and 

 so it is called the Great 

 Plains. It is probable 

 that this vast expanse 



A HIGH DRY PLAIN IN CENTRAL NEVADA 



