32 C. R. Keyes — Loess Mantle and Kansan Drift-Sheet. 



Art. IV. — Relations of Missouri River Loess Mantle and 

 Kansan Drift-Sheet ; by Charles R. Keyes. 



For the enormous deposits of loess which border the Missouri 

 River a glacial origin has never proved a very satisfactory 

 explanation. Their genetic relations have long continued to 

 be one of the most puzzling geologic problems of the region. 

 Regarding them as wind-formed accumulations has only par- 

 tially removed the difficulties presented. There have always 

 remained many seeming incongruities. 



So long and so closely have the southern limits of the drift- 

 sheet, a remarkable belt of Bluff deposits, or loess, and the 

 course of the Missouri River been associated with one another 

 that something of a genetic relationship between them has 

 been often inferred. The older glacial boundaries practically 

 follow the course of the river from its headwaters to its mouth. 

 In southeast South Dakota a younger drift-sheet also touches 

 the great stream. 



Noteworthy among the peculiarities of the loess of the region 

 are : (1) Its great thickness and conspicuous capping of the 

 bluffs on both sides of the river, a circumstance which early 

 gave it the name of " Bluff Deposit " * ; (2) its effectual man- 

 tling of the Kansan drift-sheet f ; (3) its position in many locali- 

 ties both above and below the drift X \ (4) its greater thick- 

 ness and higher elevation on the east bluff of the river than on 

 the west side, as first suggested by me in Missouri, and after- 

 wards determined by Bain in Iowa ; (5) its extension far for- 

 ward from the drift-border § ; (6) its expansion indefinitely 

 backward over the Kansan drift-sheet || ; (7) its notable non- 

 restriction to the immediate vicinity of the drift-border, but, as 

 recently shown, its extension for great distances westward from 

 the riverl" ; (8) its deposition on the surface of the country inde- 

 pendent of hypsometric conditions** ; (9) the multiple terranal 

 character which it displays in many placesff ; (10) its develop- 

 ment beneath the Kansan drift-sheet. J J 



Since presenting §§ reasons, a decade and a half ago, arguing 

 for an eolian origin of the Missouri River lcess, the conclusions 



* Swallow : Geol. Surv. Missouri, 1st and 2d Ann. Eepts., p. 69, 1855. 

 fTodd: Missouri Geol. Surv., vol. x, p. 129, 1896. 



\ Call and McGee : This Journal (3), vol. xxiv, p. 202, 1882 ; also, Todd 

 and Bain : Proc. Iowa Acad. Sci., vol. ii, p. 20, 1895. 

 §Todd : Missouri Geol. Surv., vol. x, p. 132, 1896. 

 | Bain : Iowa Geol. Surv., vol. ix, p. 91, 1890. 

 *[[ Bull. Geol. Soc. America, vol. xxii, 1911. 

 ** Calvin : Iowa Geol. Surv., vol. xi, p. 444, 1901. 

 ft Wilcox : Iowa Geol. Surv., vol. xiii, p. 716, 1904. 

 itUdden : Iowa Geol. Surv., vol. xi, p. 249, 1901. 

 §§ Keyes : This Journal (4), vol. vi, p. 299, 1898. 



