148 B. SHIMEK PLEISTOCEJsE OF SIOUX FALLS AND VICINITY 



tilted, with gray drift beneath it. In the eastern part of the same cut a 

 thick bed of fossiliferous silt occupies about the same position, but the 

 gravel and silt are not continuous, nor do they seem to be conformable. 



The arrangement of the strata in this section has been a puzzle for a 

 long time. In the light of the evidence of the McClellan Street and Da- 

 kota Avenue silt masses, already described, it is easy to conceive of the silt 

 and sand in sections 13 to 16 as displaced by Kansan ice. The amount 

 of such displacement by glacial ice has probably been generally underesti- 

 mated and will be discussed in a subsequent paper. 



Briefly, it is the writer's present view that the fossiliferous silt and 

 sand Deds in sections 13 to 15 are of Aftonian origin, but displaced by 

 Kansan ice, and that therefore the fauna of these beds is truly Aftonian. 

 It should be noted that every species of fossils, both mammalian and mol- 

 lusca]], is found also in the Aftonian beds of western Iowa. 



Kansan drift. — Characteristics of the two types. — Kansan drift has 

 been incidentally discussed in connection with the older Pleistocene for- 

 mations, and its occurrence in specific exposures is recorded in the list of 

 sections. 



In this region it presents two ordinary types : The un weathered, bluish, 

 calcareous, heavy joint-clay, with pebbles and boulders and with ferru- 

 ginous streaks and cloudings, and the softer, gray weathered type, with 

 occasional ferruginous lines and mottlings. 



The first is the more common and covers largely both the hills on the 

 Iowa side and near Sioux Falls and the plain between Shindlar and Can- 

 ton. It also makes up or covers the knobs north and northeast of Canton 

 and west of Granite on the South Dakota side, which have been regarded 

 as a part of the Altamont moraine. There can be no question concerning 

 the identity of this drift unless all the drift of Avestern and southAvestern 

 Iowa, northern Missouri, and eastern Nebraska is something other than 

 Kansan drift, for in all respects this drift is exactly like that in the 

 regions mentioned. 



Additional evidence that this is truly Kansan is found in the fact that 

 much of this drift is covered with two loesses, one bluish gray, older ; the 

 other yellow and younger. In several hundred sections in Indiana, Illi- 

 nois, Wisconsin, Missouri, Iowa, T^ebraska, South Dakota, and Minnesota, 

 in which two loesses are shown, which the writer has examined in recent 

 years, he has never found the bluish gray (post-Kansan) loess in any 

 other position than immediately above the Kan?an, or its immediate 

 derivatives represented by the Ferreto and the Loveland joint-clay and 

 probably the Buchanan gravels, excepting in a few instances where there 



