C. B. Keyes — Loess Mantle and Kansan Drift-Sheet. 33 



then arrived at have been without reserve accepted by Lever- 

 ett,* Bain,f Shimek,^ Calvin,§ Udden,| and others who have 

 worked in the region. When I first set forth this evidence I 

 was inclined to derive all of the lcess-materials directly from 

 the extensive mud-flats and sand-bars which line the great 

 stream. These sources no doubt are more than ample to sup- 

 ply the necessary matter for the loess deposits as they appear 

 to-day ; yet it now seems probable, in the light of wider investi- 

 gations, that a greater part of the silty materials comes from 

 more distant localities. Although, at the present moment, 

 quantitative determinations are not available, the volume of 

 wind-borne dusts derived from the dry, upland plains to the 

 west and settling upon and beyond the Missouri River belt 

 must be very great. The latest considerations on this point 

 suggest that not only the contiguous country and the semi- 

 arid belt but the desert regions of southwestern United States 

 are large contributors to the loess of the Mississippi Valley. 



Notwithstanding the fact that it had been long known that 

 the Missouri River loess extended forward from the limits 

 of the drift, there has been little attempt to ascertain the prob- 

 able distances. In all physical respects, except perhaps color, 

 the loess is indistinguishable from the so-called " Plains marls," 

 which so deeply mantle the surface of Kansas and Nebraska ; 

 and it cannot be told from the adobe soils of the arid regions 

 that are unquestionably accumulations of wind-blown dusts. 

 The recognition of the identity of the three deposits not only 

 greatly simplifies the consideration of their origin, but it indi- 

 cates clearly the complete independence of formation of the 

 loess and the drift. The similarity in physical characters is 

 more than co-incidental ; and once the comparison is made of 

 the three soils in the field there remains no hesitancy in pro- 

 nouncing them identical in origin. 



What is really presented by the drift and loess sections at 

 the Missouri River is a marked overlap of eolian dusts coming 

 from the southwest and of glacial deposits derived from the 

 northeast. In spite of the fact that the eolic formations attain 

 vast development in the region under consideration, their true 

 relations and character are greatly obscured by the vigorous 

 action of the rains, this belt being within the influence of moist 

 climate ; they are confused by the presence of extensive glacial 

 formations ; they are easily misinterpreted because the typical 

 deposits have never been traced forward from the glacial 

 boundary ; and they are not generally critically examined by 



* Zeitschrift f . Gletscherkunde, iv, p. 299, 1910. 

 f Iowa Geol. Surv., vol. ix, p. 91, 1899. 

 JProc. Iowa Acad. Sci., vol. xiv, p. 247, 1907. 

 | Iowa Geol. Surv., vol. xi, p. 442, 1901. 

 i Ibid., vol. xi, p. 248, 1901. 



Am. Jour. Sci. — Fourth Series, Vol. XXXIII, No. 193.— January, 1912. 

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