GREAT EROSION AL WORK OF WINDS 



473 



The distinctive feature of this great new conception of regional eola- 

 tion is that under the favorable climatic conditions of aridity such as 

 effect more than one half of the entire land-surface of our globe wind- 

 scour is the chief agency of provincial lowering and leveling, far more 

 rapid and efficacious than any general work by rain, river or ocean. To 

 it are ascribed all the larger lineaments characteristic of arid lands. 

 By it are graved the majority of desert details. It is the dominant 

 sculpturing power in all excessively dry regions. 



In a district undisturbed by mountain-making forces even plains 

 are produced, smoother than any peneplain possibly can be, and yet 



Fig. 6. Panorama of Lava-waste on Edge of New Mexican Desert ; viewed from 

 point 8,000 feet above plain ; central butte 15 miles distant. 



standing at a level high above that of the sea; such are the Kalihari 

 and elevated South African veldt, recently so graphically described by 

 Passarge, Bornhardt and others. Elsewhere, when open-patterned oro- 

 genic structure prevails, broad valleys and lofty flat-topped highlands 

 persist, as in Turkestan, lately noted by Davis, Huntington and Fried- 

 erichsen. Our own southwestern country, with its close-patterned 

 structure, presents still other phases, remarkable as the most perfect of 

 all typical Inselberglandschaften. 



Singularly enough, the great law of the base-level of erosion, the 

 most useful in all geologic science, had its birth under the cloudless 

 skies of desiccated lands where in reality no vestige of its operations is 

 discernible. The grand generalization applies strictly to land-surfaces 

 under humid climates. Doubtless for this reason it is that none of our 

 numerous government experts, in their fifty years' experience covering 

 every part of the vast arid domains of the West, failed to perceive any- 



