IOA7A ACADEMY OF SCIENCES. 77 



-which may or may not be accompanied by a black soil. This 

 reddish-brown surface appears to have been developed in all 

 places where there was fairly good -drainage. But in 

 places where the drainage was imperfect a black muck of con- 

 siderable depth accumulated and the reddened zone was imper- 

 fectly or not at all developed. In western Illinois the exposures 

 of a black soil at the base of the loess are relatively few, but 

 the reddened till surface is a common feature in every town- 

 ship. In much of the white clay district of southern Illinois 

 and in portions of the Sangamon drainage basin a black soil is 

 well developed. A black soil is also well developed in south- 

 eastern Iowa. Where the black soil is best developed leaching 

 is found to have extended in places only 1 to 2 feet into the 

 underlying till, but it often extends to a depth of six feet or 

 more. Where the black soil is absent the leaching generally 

 extends to a depth of six feet below the base of the loess. The 

 variations in depth of leaching appear to depend on the condi- 

 tions for percolation of water, being greatest where percolation 

 is most rapid. 



Noteworthy exposures of the Sangamon soil. — A few instances 

 of the exposures of this soil are selected which will illustrate 

 the variability in its character. The first section, at Ashland, 

 111., is near the place where Professor Worthen reported its 

 occurrence. 



The following series of drift beds was penetrated by a coal 

 shaft at Ashland, the identifications being made by the writer 

 irom samples of the material preserved at the engine house: 



FEET. 



Soil li 



Yellow loess, fossiliferous 9 



Blue loess fossiliferous 2 



Peal with black sandy slush 22 



Bluish gummy clay with few pebbles 20 



Yellow till \ 30 



Total drift 85 



At the air shaft sand was found in the place of blue gummy 

 clay beneath the peaty slush. A similar thick bed of peat has 

 been noted at several other points in that region, one of the 

 most conspicuous being in a well at Virginia City made by 

 Mr. Oldridge. The peat was entered at the base of the loess 

 sX about fifteen feet and continued to a depth of twenty- eight 



