176 Dr Johannes Walther — The North American Deserts. 



is able to detach and sweep down a much larger amount of 

 debris which afterward the Colorado carries out into the gulf of 

 California. 



Thus we see in the canyon of the Colorado an interesting ex- 

 ample of the combined action of erosion and deflation. We 

 recognize in the inner gorge a simple channel of erosion ; we ob- 

 serve that the upper amphitheaters OAve their existence to the 

 cooperation of erosion and deflation. 



Now, what we here see in the Colorado, that we see every- 

 where on earth where the soil is not covered by a mantle of 

 water, snow or vegetation. There is no need of traveling into 

 the deserts in order to recognize the denuding activity of wind ; 

 and in the driest desert the traces of erosion may be observed. 

 There is no region absolutely devoid of precipitation, and, on 

 the other hand, deflation may be observed in the rainiest climate. 

 When on a dry autumn day you walk along the highway and 

 are annoyed by whirling clouds of dust, you are witnessing the 

 denuding effect of wind. Every sand dune is the result of the 

 same force. Every clay bed (" Lehmlager ") teaches how vast 

 deposits are produced by wind, and the loess beds of China are 

 supposed to be merely a product of deflation. We say of the 

 wind that it " sweeps " over the gr.ound ; for this word means 

 nothing else than that the wind cleans the ground of all loose 

 particles that cover it. Translated into technical geologic lan- 

 guage, it is called " deflation," but that means nothing else than 

 the every-day word "sweep." 



-One must learn to recognize the sweeping activity of the wind 

 not only in the desert but everywhere, and in so doing to de- 

 tect in its very beginning the process whose final product von 

 Richthofen sees in the loess. 



