236 LIFE OF THE PLEISTOCENE 



Todd 73 records a dark old soil in the Big Sioux Valley, Minnehaha County, 

 east of Sioux Falls, between two till sheets, and lists certain mollusks from the 

 same horizon. Wilder 74 has published a section in which these mollusks occur. 

 According to Carman 75 and Shimek, 76 the territory in the immediate vicinity 

 of Sioux Falls is covered by Kansan drift, and hence the strata containing life 

 which lie beneath the till must be Aftonian. There is no Wisconsin till in this 

 region. Wilder's section and list of fossils appear below: 



Cutting on I. C. RR., one half mile cast of Sioux Falls. 



5. Sandy loess, in places sand 1-3 feet. 



4. Drift, unoxidiaed, with fresh pebbles 6-10 feet. 



3. Silt, slate color, with shells 3 feet. 



2. Gravel, stained, partially decayed 1-2 feet. 



1. Drift with ferretto very distinct 15 feet. 



The following fossils have been reported from No. 3. 



Planorbis bicarinatus (=antrosus) Sphaerium sulcatum ( = simile) 



" parvus Vallonia costata (1 specimen) 



Pkysa heterostropha Mud turtle 



Galba caperata . Equus species (cervical vertebrae) 



Valvata tricarinata Smaller bones (undeterminable) 

 Pisidium compressum 



From near "the brewer}', " in Sioux Falls, two species of mollusks have been 

 recorded: Galba caperata and Planorbis albus. 



Recently, Shimek has given special attention to the region about Sioux 

 Falls and many sections are described by him which contain fossils referable to 

 the Aftonian interval. 77 



At the Otis mill-site section, in Union County, situated on the west side 

 of the Big Sioux River, opposite Chattsworth, Iowa, a dark fossiliferous silt 

 resting on the Cretaceous, contains the following mollusks: 



Planorbis bicarinatus ( = antrosus) Amnicola species 



" dilatatus Pisidium species 



Segmenlina armigera Sphaerium sulcatum (=simile) 



Physa gyrina Unio, fragments 



Galba reflexa Pyramidula cronkhitei anthonyi 



" humilis modicella Strobilops, fragment 

 Valvata tricarinata 



In Sioux Falls the sections indicate that the Kansan ice ploughed up the 

 Aftonian Interglacial silts, causing them to lie between two beds of Kansan 



"Proc. Iowa Acad. Sci., VI, pp. 122-130. 



u Geol. Iowa, X, p. 127. 



' 6 Proc. Iowa Acad. Sci., XX, pp. 237-250. 



'• Bull. Geol. Soc. Amer. XXIII, pp. 125-154. 



" Bull. Geol. Soc. Amer., XXIII, pp. 125-154, 1912. 



