76 IOWA ACADEMY OF SCIENCES. 



Kansan till sheets. The name Buchanan may still have the- 

 significance given it by Professor Calvin; and if weathering be 

 included may, perhaps, be used to cover the time involved in. 

 the two interglacial stages with the intervening glacial stage. 



THE SANGAMON WEATHERED ZONE. 



Earliest iZecof/ni^ion. — Apparently the first recognition of the 

 occurrence of a definite soil horizon between the lowan loess 

 and the lUinoian till sheet is that reported by Prof. A. H. 

 Worthen, in the Geology of Illinois (*). In his report on Sang- 

 amon county, Illinois, made in 1873, Professor Worthen called 

 attention to a soil found at the base of the loess in Sangamon 

 and neighboring counties. The soil apparently was first noted 

 by Mr. Joseph Mitchell, in the excavation of wells in the north- 

 west part of the county, and in neighboring portions of Menard 

 county. Mr. Mitchell furnished for publication in the Geology 

 of Illinois the following section of the beds usually penetrated: 



FEET. 



Soil 1 to 2i 



Yellow clay 3 



Whitish jointed clay with shells 5 to 8 



Black muck with frag-ments 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 undoubtedlj'^ 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. 



General prevalence of a 10 iathered zone at the base of the Towan 

 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 feature which suggests that there was not much oxidation 

 and leaching or else there was subsequent deoxidation. The 

 more common phase is a reddish- brown till surface for which 

 Dr. H. P. Bain has proposed the Italian name "ferretto" (f) 



(*) Geol. of llli'io's, Vol. V. 1873, gp. 306 to 319. 



(+) Ste. Pioc. Iowa Acad, of Sciences, Vol. V, 1898, p. 91. 



