DEFLATION OP ARID LANDS 581 



deflation, and aeroposition, the equivalents of rock decomposition, trans- 

 portation, and deposition. 



DESTRUCTIVE VERSUS CONSTRUCTIVE EOLATION 



Singularly enough the work of the wind generally has been treated 

 from the side of its constructive rather than of its destructive effects. 

 Drifting sands of the seashore and kindred phenomena have been 

 commonly cited in illustration. So preponderant have been the building 

 up effects supposed to be over the denuding effects that the latter have 

 almost invariably received scant notice. Eussell,^^ along with others, 

 has even gone so far as to explain the vast intermont plains of the 

 Great Basin region as formed by wind-blown soils accumulating to the 

 great thicknesses of 2,000 to 3,000 feet and more, burying the mountains 

 up to their shoulders. This, however, is an extreme view of eolian depo- 

 sition, and in the light of more recent observation must be greatly 

 modified. 



That the wind in the role of a general denuding power is comparable, 

 under favorable climatic conditions, to ordinary water action in a humid 

 climate has never received special attention. Until quite lately this 

 phase of wind work has been passed by without exciting extended com- 

 ment. Several writers have, however, recently incidentally alluded to it. 

 Petrie,^^ for instance, estimates that along the Isthmus of Suez the coun- 

 try has been cut down by the wind at the rate of about 4 inches in a cen- 

 tury. A more vigorous rate of wind excavation is described by Dwight,^^ 

 in the Cape Cod district of Massachusetts, where in a short time sands 

 were blown away to depths of 10 feet and more. It remained for Pas- 

 sarge^^ to emphasize the great denuding powers of the wind and its action 

 as an important agent of general desert-leveling. Walther,^^ Penck,^^ 

 and others have recognized far-reaching possibilities of wind scour, par- 

 ticularly in dry regions. 



PLAINS-FORMING TENDENCY OF WIND ACTION 



The most manifest effect of wind erosion in an arid land is the forma- 

 tion of plains in a manner and on a scale that finds no parallel among 

 water-formed plains. As Davis^* well observes, the scheme of the arid 



28 Geological Magazine, Decade ill, vol. vi, 1889, p. 242. 



29 Proceedings of the Royal Geographical Society, 1889, p. 648. 



30 Travels in New England and New York, vol. ill, p. 101. 

 aiZeitsch. d. deut. geol. Gesellschaft, LVI Bd., Protokol, 1904, p. 193. 

 32Das Gesetz der Wiistenbildung, Berlin, 1900. 



33 American Journal of Science (4), vol. xix, 1905, p. 165. 

 »* Journal of Geology, vol. xiil, 1905, p. 395. 



XLI— Bull. Geol. Soc. Am., Vol. 21, 1909 



