584 C. R. KEYES — ^RELATIVE EFFICIENCIES OF EROSIONAL PROCESSES 



water action, and especially with water as the most familiar of the erosive 

 agencies, the effects of eolation are apt to be largely overlooked. Eolation 

 is probably an important erosive process far beyond the limits of the arid 

 region, its influence rapidly diminishing as the annual amount of rain^ 

 fall increases. For instance, the eastern boundary of the American arid 

 region may be taken as the western line of Texas and Kansas, but eolative 

 influences are appreciable and important so far east as the Missouri Eiver, 

 and even beyond. 



Some observations on wind erosion have already been recorded from 

 the Great Plains region. Winchell graphically describes the powerful 

 effects of wind scour in the Dakotas. The possible eolian origin of the 

 great loess deposits along the Missouri Eiver has been recently advanced 

 by me.*2 



The region between the arid belt and the Missouri Eiver, known as the 

 Great Plains, was not so very long ago believed to owe its smoothness 

 chiefly to the fact that it was once occupied by Tertiary lakes. Later 

 it was thought that the plains expression was largely the result of fluvia- 

 tile deposition. It now appears more probable that these plains were 

 fashioned mainly by eolation. 



EXTENT AND VOLUME OF EOLIAN TRANSPORTATION 



I do not know that any serious attempts have been yet made to measure 

 the transportative powers of the winds in desert regions. As I have noted 

 recently,*^ the effects of "dust-storms" or "sand-storms" in the arid dis- 

 tricts in producing personal discomforture are so marked that they have 

 commonly blinded all, even the trained scientist, to their real geologic 

 significance. The tremendous power of the sand-storm on the Sahara 

 and Arabian deserts have been known from earliest historic times ; but it 

 has been regarded as merely a freak of idle, shifting sands, rather than of 

 a forceful and persistent geologic agent. Some of the geologic effects of 

 the wind have been discussed recently by Walther,** whose observations 

 were made chiefly on the northern African deserts. Similar wind effects 

 on the bare sand bars of the Missouri Eiver reproduce on a small scale 

 and under humid climate the conditions of great desert regions. 



The "sand-storm" of the desert is really a thing to be feared by the 

 traveler. To be fully appreciated it has to be experienced. On the inter- 

 mont plains of southwestern United States "dust-storms" are of frequent 

 occurrence and they last several days. The volumes of soil flowing along 



« American Journal of Science (4), vol. vi, 1898, p. 299. 



»3 Bulletin of the Geological Society of America, vol. 19, 1908, p. 81. 



*» Abhand. Koniglichen Sach. Gesellschaft d. Wissensch., XVI Bd., 1891, pp. 345-570. 



