GREAT EROSION AL WORK OF WINDS 



469 



Pig. 2. Wind-graved Cliffs of the Mokattam Iln.i.s ; on the borders <>C tlio 



Arabian desert opposite Cairo, Egypt. 



as mighty as any swept into the seas by streams or laid down on the 

 floor of the ocean, are new and important generalizations belonging dis- 

 tinctly to the first lenstrum of our new century. 



Prior to the year 1900 wind-action had been alw.iys regarded as 

 merely one of the minor geologic agents of erosion — a mere idler in its 

 manifestations, and a denuding power at all times negligible. That its 

 real role in geologic economy had been so long so completely overlooked 



L *&r '■■■ -'• • <■ 





Fig. 3. Sharp Meeting of Hard Mountain ROCK and Soft Plains Stisaia; 

 Torreon, Mexico — a characteristic feature of regional eolation. 



