CONTROLLING EROSIONAL AGENTS 541 



may be made of the work of Obruchew/ in central Siberia ; of Walther,® 

 in north Africa; of La Touche/'' in the western Eajputana, in India; 

 of Berg^^ and Ivchenko/- in the region about the Sea of Aral and on 

 the Kirghiz steppes; of Passarge^^ and of Davis/* in the South African 

 veldt; of Penck;^^ of Hundhausen/® in southern France; of Barron, ^^ 

 in eastern Egypt, and of Blackwelder/^ in Wyoming. 



Eecent investigations in arid and semi-arid countries appear to dem- 

 onstrate beyond all shadow of doubt that as a denuding, transportive, 

 and depositional power the wind is not only fully competent to perform 

 such work, but that it is comparable in every way to water action in a 

 moist climate. As lately noted,^^ it is significant that most of the broad 

 intermont plains of the Southwestern Desert, for instance, should be 

 areas of rapid degradation instead of aggradation, as is shown by their 

 remarkable rock-floors, that the little normal water action therein should 

 be confined to the loftier mountains, and that the general plains surface 

 should be so little affected by stream corrasion. General desert leveling 

 and lowering must find for their chief sculpturing agency something 

 other than stream action. All things considered, deflation, or wind- 

 scour, in arid lands not only appears to be the principal erosional 

 process, but water action surprisingly subordinate. 



Under conditions of aridity the relative efficiencies of wind-scour and 

 water action may be roughly measured by the circumstance that the total 

 volume of rock-waste brought down by storm waters, from a desert range 

 in a year may be removed by the winds in a single day. What general 

 erosion by means of water is in a wet climate, eolation is under condi- 

 tions of arid climate. 



EXTENT OF ICE SCORING IN A GLACIAL CLIMATE 



Erosion by ice under conditions of a true glacial climate is probably 

 not nearly so vigorous, widespread, or important as it has been thought 

 to be. Further, it may be questioned whether in the case of great conti- 

 nental ice-fields there is sufficient motion except near the melting mar- 



8 Verb. Imp. min. Gesellsch., St. Petersburg, vol. xxxiii, 1895, p. 260. 



» Das Gesetz d. Wiistenbildimg im Gagenwart u. Vorseit, 1900. 



1° Mem. Geol. Survey India, vol. xxxv, 1902, p. 10. 



^ P^dologie for 1902, p. 37. 



^ Ann. geol. min. Russie. vol. vli, pt. i, 1904, p. 43. 



13 Zeitsch. d. dents, geol. Gesellscb., vol. Ivi, Protokol, 1904, p. 193. 



i*Bull. Geol. Soc. America, vol. 17, 1906, p. 435. 



1^ American .Tournal of Science (4), vol. xix, 1905, p. 167. 



"Globus, vol. ex, 1906, p. 46. 



"Topography of Sinai, western portion, 1907, p. 17. 



18 Journal of Geology, vol. xvil, 1909, p. 429. 



i»Bull. Geol. Soc. America, vol. 21, 1910, p. 587. 



