144 B. SHIMEK PLEISTOCENE OF SIOUX FALLS AND VICINITY 



and broken shells), full}' 20 feet long and 4 or 5 feet deep, and present- 

 ing the appearance of having been pushed by drift moving from the 

 north. Another mass of similar silt occurs in Kansan drift on the west 

 side of Dakota Avenue, north of West Third Street. Here a mass of 

 dark silt, in places more than 3 feet deep, is exposed for fully 75 feet. 

 This mass dips downward to the south, and evidently is not silt deposited 

 in situ, but moved by Kansan ice. 



TERRACE OR BENCH SECTIONS 



The foregoing sections, and many others like them, show the structure 

 of the Pleistocene of the uplands, but there are also sections in the ter- 

 races, or benches, which are so conspicuous in the Big Sioux Valley. The 

 more conspicuous terrace sections are here discussed in detail. 



17. Fairview gravel pit. — This is located along the Chicago, Milwaukee 

 and Saint Paul Eailway, 1 mile south of Fairview, South Dakota. Here 

 30 feet of gravel rest on a bed of tough, typical blue-black Xebraskan 

 drift, which is separated from the gravel by a tough, reddish, laminated 

 silt-band. The j^ebraskan is blue-black, tough, and contains planed 

 boulders. 



18. Klondike section. — This is located in a gully in the terrace Just, 

 east of Klondike bridge, and shows 20 feet of cross-bedded sand and 

 gravel, with the uppermost 2 or 3 feet crowded with boulders, resting on 

 a bed of gray, in part blue, very tough joint-clay, which is probably Xe- 

 braskan. Springs flow abundantly from the gravel. 



19. Section west of KlondiJi-e. — This is located on the west side of the 

 river opposite Klondike. It follows the edge of the bench or terrace and 

 shows an exposure of 15 feet of typical blue-black Xebraskan, on which 

 rest about 10 feet of sand and gravel. This is then covered with soil to a 

 depth of 1 to 2 feet. This is one of the finest exposures of Xebraskan 

 observed in South Dakota. Along almost the entire length of this ex- 

 posure springs flow freely from the base of the gravel. 



20. Sections along the north side of section 17, toirnship 99 north. 

 range 48 ivest. — These sections, three in number, are exposed along a 

 small creek about a mile northwest of Klondike, and show gravel resting 

 on a gray or blue-black pebble-bearing Xebraskan ( ?). Tlic eastern sec- 

 tion, vshown in plate 9, figure 2, shows a bench of typical blue-black 

 Nebraskan, 4 to 5 feet exposed, supporting a bed of coarse gravel 4 to 5 

 feet thick. The westernmost section shows a hard gray bed, probably 

 Nebraskan, exposed about 2 feet at the base, and on it there is a con- 

 glomerate stratum about 2 feet thick, on which rest 6 to 15 feet of loose 

 gravel, Numerous springs flow from the gravel. 



