l38 B. SniMEK rLEISTOCENE OF SIOUX FALLS AND ^^CINITY 



been considered older Kansan in this general region, but its position 

 below a fossiliferous silt and sand and its dark color indicate that it is 

 N"ebraskan. Some of its portions are certainly like the coarser Xebraskan 

 at Council Bluffs and Omaha. 



The Aftonian silt, which is sharply set off from the Kansan drift 

 above, but blends with the Aftonian sand below, is whitish, very calcare- 

 ous, *and contains shells of fresh-water mollusks of the usual Aftonian 

 type. 



The Kansan is typical, and at the very top of the ridge is covered with 

 a thin layer of yellow loess. The slopes are liberally dotted with Kansan 

 boulders. 



Other sections appear both above and below section 4. 



5. Section south of Klondike, Iowa. — This is located in Lyon County, 

 in section 21, township 99 north, range 48 west, at the point of the bluff 

 south of the creek below Klondike. It presents the following: 



Kansan, t3^pical, 15 feet exposed. 

 Aftonian : 



Loose sand and gravel, about 24 feet. 



Conglomerate, forming a projecting ledge, 5% feet. 



White, calcareous, marly stratum, probably Aftonian, 5 feet. 

 Nebraskan, typical, more or less exposed to creek, 15 feet. 



This Aftonian is on a level with the bed of gravel in the near-by ter- 

 races. 



Another exposure just east shows about 40 feet of Kansan, with 

 numerous sand boulders and sand lenses, especially in the lower part, 

 indicating that the Kansan plowed the Aftonian sands. 



6. Peterson section. — This is located on the west side of the river just 

 above Klondike. Here a bed of apparently Aftonian sand and fine gravel 

 rises to a heiorht of 20 feet above the river bottoms and is covered bv a 

 mass of typical Kansan, which evidently forms the bulk of the bluff. 

 Along the line of contact the Kansan and Aftonian are more or less 

 mixed. 



This section is opposite the great Klondike terrace. 



Several exposures along the bluff above the Peterson section show 

 Aftonian, which in some cases reaches a height of over 30 feet above the 

 bottom lands. This is uniformly below Kansan drift and gives rise to 

 numerous springs. 



7. Nicholson bridge section. — This is located east of the Nicholson 

 bridge, in section 6, township 99 north, range 48 west, Lyon County, 

 Iowa. It shows : 



