286 LIFE OF THE PLEISTOCENE 



and because of the conspicuous development in the Sangamon drainage basin, 

 it seems appropriate to name it the Sangamon Interglacial Stage." 2 



A typical generalized section of the strata in Sangamon County is given 

 by Leverett, after Worthen, and is reproduced below: 



Soil 1-2 feet 



Yellow clay (Iowan loess) 3 " 



Whitish (gray?) jointed clay, with shells (Illinoian loess) 5-8 " 



Black muck with fragments of wood (Sangamon soil) 3-8 " 



Bluish colored boulder clay (Illinoian drift) 8-10 " 



Gray hardpan, very hard (Illinoian) 2 " 



Soft blue clay, without boulders 20-40 " 



This interval is widespread in Illinois, but is not always represented by 

 muck beds. Sometimes it is represented by a leached and somewhat reddish 

 deposit which has been called the 'ferretto' zone by Dr. H. F. Bain. 3 In some 

 areas there is an alternation of sand with peaty beds, this phase being restricted, 

 apparently, to the borders of valleys where stream action has been more or 

 less active, intermittently. The blue loess is also to be included in the Sanga- 

 mon interval, and is to be separated from the upper yellow or Iowan loess. 

 The Sangamon is considered first in those states in which it covers the exposed 

 Illinoian drift, and later in those states to the north and northeast in which 

 this drift sheet is covered by the Wisconsin till. 



B. DISTRIBUTION OF THE SANGAMON BIOTA 

 1. IOWA 



As has already been stated, the Illinoian ice sheet invaded Iowa, pushing 

 the Mississippi River westward for several miles. Illinoian drift is found near 

 Fort Madison northward to near the northern boundary of Scott County. In 

 this area a number of deposits occur which are referable to the Sangamon 

 interval. In Des Moines County, near Burlington, a section exposes the 

 following strata: 4 



1. Brownish yellow clay free from gravel, grading into No. 2 (Iowan loess) 5 feet 



2. Typical ashen compact loess (Illinoian) _ 8 " 



3. Till with abundance of gravel and pebbles (Illinoian) 20 " 



Height of section 33 feet 



2 Leverett, Illinois Glacial Lobe, p. 125; Proc. Iowa Acad. Sci., V, p. 71; Worthen, Geol. 

 111., V, pp. 306-319. 



J Proc. Iowa Acad. Sci., V, p. 91. 



4 Keyes, Iowa Geol. Surv., Ill, p. 156. 



