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THE POPULAR SCIENCE MONTHLY 



is now measurable to something of its true proportions. A " sand-storm " 

 or " dust-storm " is really a strong desert air-current two or three hun- 

 dred miles in width instead of a mile wide as in the case of the largest 

 rivers, running forty miles an hour instead of three or four miles, and 

 sweeping along a thousand times as much sedimentative materials. 

 Only by such comparison is the enormous erosive potency of deflative 

 action fully comprehended. 



Wind-formed deposits are mainly laid down far outside the confines 

 of deserts — in the moist verdure-clad lands, or in the sea. Their mag- 

 nitude is very great, as the enormous loess formations, the vast expanses 

 of black soils of the steppes and prairies, and the extensive adobe clays 







Fig. 9. An Oasis in an American Desert (Southern New Mexico). 



of many parts of the world amply attest. Continental deposits of this 

 origin are just beginning to receive from scientists the attention which 

 they merit. 



The law of regional eolation will rank high among modern geolog- 

 ical discoveries. What William Smith's discovery of characteristic 

 fossils for identifying geologic terranes was to stratigraphy and his- 

 torical geology, what Bunsen's theory of magmatic differentiation was 

 to modern petrology, what Agassiz's hypothesis of continental glaciation 

 was to recent geologic history, and what Powell's law of the base-level 

 of erosion was to physiography of to-day, so the general theory of defla- 

 tion, or regional eolation, is to the sciences of desert landscape sculptur- 

 ing, and the formation of continental deposits as vast as any laid down 

 on ocean borders. The theory adequately explains a grander host of 



