THE WEATHERED ZONE 177 



Feet 



Soil, ItO 2^ 



Yellow clay, ------- 3 



Whitish jointed clay with shells, - - - 5 to 8 



Black muck with fragments of wood, - - 3 to 8 



Bluish colored bowlder clay, - - - - 8 to 10 



Gray hardpan — very hard, ----- 2 



Soft blue clay without bowlders, - - - 20 to 40 



Professor Worthen states that the bed overlying the black 

 muck is undoubtedly loess, also that the black muck indicates 

 conditions suitable for the growth of arboreal vegetation in the 

 interval between the deposition of the bowlder clay and the 

 overlying loess. The name Sangamon is taken from this local- 

 ity where the soil was first reported. 



Geiieral prevalence of a weathered zone at the base of the Iowan 

 loess. — In the locality just mentioned there appears to be only a 

 bed of muck to indicate the interval between the deposition of 

 the bowlder clay and that of the overlying loess, for the clay 

 immediately below the muck is described as of a blue color, a fea- 

 ture which suggests that there was not much oxidation and leach- 

 ing, or else that there was subsequent deoxidization. The more 

 common phase is a reddish brown till surface for which Dr. H. 

 F. Bain has proposed the Italian name "ferretto," 1 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 considerable depth accumulated and 

 the reddened zone was imperfectly 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 com- 

 mon feature in every township. In much of the white clay dis- 

 trict of southern Illinois and in portions of the Sangamon drain- 

 age basin a black soil is well developed. It is also well developed 

 in southeastern Iowa. Where the black soil is best developed 

 leaching is found to have extended in places only one to two 

 feet into the underlying till but it often extends to a depth of 



J See Proc. Iowa Acad, of Sciences, Vol. V, 1898 (in press). 



