IOWA ACADEMY OF SCIENCES 75 



by the lowan ice invasion has not been determined. The lowan 

 till certainly does not extend as far south as the Wisconsin in 

 those states. The loess forms a heavy deposit along the border 

 of the Mississippi and Illinois valleys, but is comparatively 

 thin in the region east of the Illinois, its average thickness 

 being scarcely 10 feet. A silt tentatively correlated with the 

 loess covers the Illinoian till sheet, wherever exposed outside 

 the Wisconsin, from the Illinois river eastward to central Ohio. 

 The Sangamon weathered zone between the loess and the 

 Illinoian till sheet is found from central Ohio westward to south- 

 eastern Iowa. i. e , to the limits of the Illinoian till sheet. The 

 lowan loess extends also over the Kansan tillsheet of southern 

 Iowa and adjacent portions of Missouri, Kansas and Nebraska, 

 but this loess is separated from the underlying till by a much 

 longer interval than that between the loess and the Illinoian till 

 sheet, an interval comprising two interglacial stages and one 

 glacial stage. 



Application of Bach'inaa. — -At the tenth annual meeting of this 

 Academj^ Prof. Samuel Calvin, after describing certain gravel 

 deposits in northeastern Iowa, introduced the term Buchanan 

 as a name for an interglacial stage following the Kansan (1), 

 and made the following statement concerning the origin and 

 age of the deposits: 



" As to their origin the Buchanan gravels are made up of 

 materials derived from the Kansan drift. As to age they must 

 havQ been laid down in a body of water immediately behind the 

 retreating edge of the Kansan ice. " 



Manifestly the deposition of the Buchanan gravels covers 

 but a small part of the time between the Kansan retreat and the 

 lowan advance. Unless, therefore, the deposition and subse- 

 quent weathering both be included under this name it does not 

 fill an interglacial stage. Were there no Illinoian glacial stage 

 to break the continuity of interglacial conditions from the 

 Kansan to the lowan stage of glaciation it would not seem 

 necessary to look for other terms. But in view of this glacial 

 interruption there seems need for names which will stand for 

 the weathered zones above and below the Illinoian till sheet. 

 It is for this reason that the name Sangamon is here suggested 

 for a weathered zone separating the Illinoian till from the over- 

 lying loess. In an accompanying paper the name Yarmouth is 

 introduced for the weathered zone between the Illinoian and 



(U Proc. Iowa Acad, of Sciences, Vol, III, 1896, pp. 58-60. 



