CHAPTER VIII 



THE KANSAN ICE INVASION AND THE YARMOUTH INTERGLA- 



CIAL INTERVAL 



I. The Kansan Ice Invasion 



Following the Aftonian Interglacial interval, climatic conditions again 

 became severe and a second ice sheet, the Kansan, advanced and covered a 

 large portion of the United State ; (Plate XLVI). East of the 110th meridian 

 the ice sheet extended a short distance south and west of the Missouri River in 

 Montana, the Dakotas, Nebraska, Kansas and Missouri. The largest known 

 lobe extended southward west of the Mississippi River and the driftless area, 

 spreading entirely over Iowa and entering Nebraska, Kansas, and Missouri, 

 as well as a narrow strip in western Illinois. 



Another lobe entered Illinois but its extent is not known as it is completely 

 covered by the later Illinoian ice sheet. The Kansan has been definitely 

 located beneath the Illinoian till, however, and its presence is beyond question. 

 The extent of this till beneath later glacial deposits is not known. An old 

 till sheet is known in northern Pennsylvania, but whether it is Kansan or 

 Nebraskan has not been definitely determined. 1 



The Kansan ice picked up pieces of wood, tree trunks and branches and 

 other material on the surface of the Aftonian soil. In some places, as in 

 Monona and Harrison counties, Iowa, the Kansan ice ploughed up the Aftonian 

 and Nebraskan deposits, either incorporating the frozen gravel and sand in the 

 base of itself, or pushing these deposits until they were either vertical or 

 actually lay over the Kansan deposits. 2 



II. The Yarmouth Interglacial Interval 



This interglacial interval is better developed and has been more fully 

 studied in the states of Iowa and Illinois. The sands, gravels, silts, and 

 mucks have preserved a well marked fauna of which the largest number of 



1 Consult the following references for information on this point : 

 Butts, Warren Folio, U. S. Geol. Surv., No. 1 72, pp. 6-7. 

 Leverett, Mon. U.S. Geol. Surv., XLI, pp. 253-254. 

 Munn, Sewickley Folio, U. S. Geol. Surv., No. 176, p. 6. 

 Willard, Tower Folio, U. S. Geol. Surv., No. 168, p. 2. 

 Williams, Proc. Amer. Phil. Soc, XXXVII, pp. 84-87. 

 2 Shimek, Iowa Geol. Surv., XX, p. 351. 



