20 



THE POPULAR SCIENCE MONTHLY 



Navajo Church, New Mexico. Ponderous pinnacles of eolian erosion, rising nearly 

 a thousand feet above the valley at left. (C. E. Button, photo.) 



the barren waste of popular fancy. Vast tracts of it are certain to be 

 reclaimed to the uses of mankind. Some of it is doubtless to become 

 the most eagerly sought of all estates. Its beauties and its treasures 

 are only beginning to be understood. Even scientists have only com- 

 menced to turn their attention seriously to the make-up, features and 

 resources of the so-called desert regions. 



The idea of a base-level of erosion, lying but slightly above tide, 

 but below which stream-corrasion can not go, has done for geography 

 what the principle of evolution has accomplished for biology. It is, 

 in fact, the evolutionary principle applied to land sculpture. This 

 theory of Powell's is justly regarded as one of the three grand deduc- 

 tions which geology of the century just past has bequeathed to science. 

 Conceived midst the arid regions of the West, its widest influence has 

 been in the moister countries of the earth. 



