CHAPTER VI. 



THE SANGAMON SOIL AND WEATHERED ZONE. 



Between the disappearance of the Illinoian ice sheet and the deposi- 

 tion of the Iowan till and loess there occurred an interval of deglaciation 

 about as marked as that between the Kansan and Illinoian stages of gla- 

 ciation, a period marked by leaching and oxidation of the Illinoian drift, of 

 peat and soil accumulation, and of erosion. This interval was long since 

 brought to notice by Prof. A. H. Worthen in his report on Sangamon County, 

 Illinois. 1 For this reason, and because of the conspicuous development in 

 the Sangamon drainage basin, it seems appropriate to name it the Sangamon 

 interglacial stage. This name was suggested by the writer in a paper pre- 

 sented before the Iowa Academy of Sciences in December, 1897. 



The following section, published bv Worthen, was furnished him by a 

 well digger, Joseph Mitchell, who had dug many wells in the northwest 

 part of Sangamon County and in the adjoining portion of Menard County: 2 



Generalized section of wells northwest of Springfield, Illinois. 



Feet. 



Soil 1-2 



Yellow clay 3 



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



Black muck with fragments of wood 3-8 



Bluish colored bowlder clay 8-10 



Gray hard pan (very hard) 2 



Soft blue clay, without bowlders 20-40 



This section represents the formations beneath the upland plain near 

 the western edge of the Sangamon watershed at an altitude 200 feet or 

 more above the level of the mouth of the Sangamon. Worthen remarks 



1 Geol. of Illinois, Vol. V, 1873, pp. 306-319. -Op. cit., p. 307. 



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