GREAT EROSION AL WORK OF WINDS 471 



appears to be due to the recency and enthusiasm with which by the sci- 

 entific world the great law of the base-level of erosion had been received 

 and to the vast dynamic possibilities which it had opened up. 



Scant indeed is the attention given in the text-books on earth-history 

 to the geologic effects of wind-action. A good and concise summary of 

 our prevailing notions on the subject a decade ago is given by Udden. 

 The great significance and value of the newer generalization lies not 

 alone in the recognition of the geologic potency of wind-power as an 

 agency of erosion, or as a means of forming such vast continental 

 deposits as the loess, but of its tremendous efficiency as a general or 

 regional denuding force. In far-reaching importance it compares fa- 

 vorably with the enunciation of the glacial theory of the last century. 



It has long been the custom not only to treat the subject of general 

 land -sculpturing independently of climatic considerations, but as if the 

 molding of all landscape features was controlled by the same laws. The 

 fertility of suggestion arising from the conception of a definite cycle 

 of development through which all land-forms must pass has tended to 

 exaggerate the evolutionary aspects of the theme at the expense of the 

 genetic means by which the physiographic changes have taken place. 

 Even the latest and most authoritative treatise on physical geography 

 has premised the same deiivation of physiognomy for the glacial Alps 

 and the arid-high plateaux of western America, for the forest-clad 

 Appalachians and the barren South African veldt, for the jungle-matted 

 eastern Andes and the desert Australian interior. Ordinary stream- 

 corrasion is made to account for all. Rain is regarded as the universal 

 and sole graving-tool of land-sculpturing. 



A full comprehension of the pregnant idea that wind-action under 

 the favorable physical conditions imposed by arid climate is a general 

 erosional agent may be said to date from the year 1904 — the time of 

 the appearance of Passarge's brief but quite remarkable essay on " Die 

 Inselberglandschaften im tropischen Afrika." In various parts of the 

 world during the decade previous the conception had in one way or 

 another begun to assume form. The Trans-Caspian region had already 

 furnished some facts bearing upon the new generalization. The vast 

 deserts of the Dark Continent had supplied others. Our American arid 

 lands had brought forth a host of still different suggestions. Indeed, 

 as a definite working hypothesis the general scheme appears to have 

 been first successfully formulated and applied in the great dry region 

 of our own Southwest. 



Whether first definitely outlined by American on the Girghiz steppes, 

 by German on the South African plateau, or by Yankee on the Mexican 

 tableland, it is certain that, as McGee astutely observes, the satisfactory 

 disposal of the rock- waste of the deseit by prodigious wind exportation 

 furnishes the missing link to a rational explanation of all the long puz- 

 zling phenomena presented by arid regions throughout the world. 



