694 C. R. KEYES MID-CONTINENTAL EOLATION 



tions similar experiences. Udden^^ describes many such storms which 

 occurred during the years 1894-5. 



In referring recently to the dominant features of the region lying 

 between the Mississippi Elver and the Eocky Mountains, I made^^ the 

 observation that general deserx-leveling, ^nielly through eolation, is 

 doubtless much more extensive than has been commonly supposed; that 

 in the presence of water action, especially since water is the most familiar 

 of the erosive agencies, the effects of wind-work are apt to be largely 

 overlooked, and that eolation is probably an important aggrading process 

 far beyond the limits of an arid region, though its influence rapidly 

 diminishes as the annual amount of rainfall increases. In support of 

 these statements it was noted that while the eastern limits of the Ameri- 

 can arid region may be taken as the western boundary of Texas and Kan- 

 sas, eolative activities are appreciable so far east as the Missouri Eiver, 

 and even beyond. ^^The region lying between the arid belt and the Mis- 

 souri Eiver 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 fluviatile depo- 

 sition. It now appears more probable that these plains were fashioned 

 mainly by eolation."^^ 



AihROPOSITION EAST OF THE ROCKY MOUNTAINS 



Incidentally a number of references are made to eolian deposits on the 

 Great Plains. Cannon,^^ for instance, observes that in eastern Colorado 

 "the heavy deposits of loess that mask the entire plains country attain 

 near Wray, on the Burlington and Missouri Eiver Eailway, a thickness of 

 over 225 feet.^^ . . . "On the ^flats' between the streams the loess is 

 covered by extensive superficial deposits of eolian origin." In discussing 

 the question, "Is the White Eiver Tertiary an eolian formation?'^ Mat- 

 thew^* ascribes the sandstones to possible river action, but the clays seem 

 best to accord with eolic activity, "such as is now going on in the produc- 

 tion of the loess on the open grassy surface of the sub-arid plains." 



That extensive wind-laid terranes are to be included among continental 

 deposits of this country is a still more recent suggestion which I have 

 made concerning the origin of the Great Plains formations.^^ As stated, 

 the important eolic deposits are to be expected on the leeward side of arid 



30 Popular Science Monthly, vol. xlix, 1896, p. 655. 



31 Bull. Geol. Soc. America, vol. 21, 1910, p. 585. 

 82 Loe. cit. 



33Proc. Colorado Sci. Soc, vol. iii, 1890, p. 215. 

 3* American Naturalist, vol. xxxiil, 1899, p. 403. 

 35 Proc. Iowa Acad. Sci., vol. xix, 1911, p. 200. 



