136 b. shimek pleistocene of sioux falls and vicinity 



Geology 

 in general 



The Pleistocene formations of this region constitute its most interest- 

 ing and conspicuous feature. In the northern part they rest directly on 

 the Sioux quartzite, and southward to Sioux City they overlie the Cre- 

 taceous. The following members are represented: Nebraskan drift; Af- 

 tonian gravel, sand and silt; Kansan drift; a bluish gray post-Kansan 

 loess, a later yellow loess, and ordinary alluvium, which needs no dis- 

 cussion. 



Practically every exposure between the northwest corner of Iowa and 

 Faindew was examined, in most cases more than once, with remarkably 

 consistent results. The sections of greatest interest naturally fall into 

 two groups : the blulf sections, which are found in the rougher portions 

 of the area, and the bench or terrace sections along the streams. A few 

 typical sections are here presented. 



. BLUFF SECTIONS^ 



1. Fairview section. — One and one-half miles west of Fairview, in sec- 

 tion 16, on the south side of the river, a slide reveals the following sec- 

 tion: 



Loess, capping the hills above. 

 Kansan, 15 feet exposed. 

 Af tonian : 



Alternating layers of silt and sand, 10 feet. 



Coarser sand and fine gravel, 10 feet. 



Nebraskan, 2 feet exposed, its top 45 feet above the river bot- 

 toms. 



The ISTebraskan is here very hard, jointed, in part gray, somewhat fer- 

 ruginous, and with very dark carbonaceous materials in the upper part. 

 The Kansan is typical, bluish, calcareous joint-cla}', with ferruginous 

 streaks and cloudings, and some pebbles and small boulders, being exactly 

 like the ordinary Kansan, which may be traced in a complete series of 

 exposures from northern Missouri and southern Iowa to the region under 

 discussion. 



The Aftonian is also typical, and its position between the Nebraskan 

 and Kansan drifts is unmistakable. 



^ The numbers of these sections appear on the map. 



