Page:Popular Science Monthly Volume 82.djvu/477

Rh The distinctive feature of this great new conception of regional eolation is that under the favorable climatic conditions of aridity such as effect more than one half of the entire land-surface of our globe windscour 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

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 orogenic structure prevails, broad valleys and lofty flat-topped highlands persist, as in Turkestan, lately noted by Davis, Huntington and Friederichsen. 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 anything