THE PEORIAN SOIL AND WEATHERED ZONE 245 



lowan drift. In central and western Illinois the soil is in places 

 underlain by a fossiliferous silt, referred with some confidence 

 to the lowan loess. In eastern Illinois the lowan till may be 

 present. This soil horizon, together with lower soil horizons, 

 was discussed by the writer in a paper presented at the Cleve- 

 land meeting of the American Association for the Advancement 

 of Science. 1 At that time the separation of the lowan sheet 

 from the Illinoian had not been made and all the soils were 

 referred to a single horizon. The later developments have led 

 the writer to separate the soils found at, or slightly below, the 

 Wisconsin drift into two classes — one class being thrown into 

 the Sangamon stage, while the other is thrown into the stage 

 under discussion. It is not possible in all cases to decide to 

 which class a buried soil should be referred, for in some cases 

 its existence is known only through well records. The separa- 

 tions thus made are set forth in detail in a report by the writer 

 yet unpublished. 



In selecting a name for the horizon, the ideal locality would 

 be one in which the earliest sheet of Wisconsin till overlies the 

 lowan till. In the vicinity of Marengo, in McHenry county, a 

 black muck has been found at the base of the Wisconsin drift, 

 and it apparently rests on lowan till. This might be taken as a 

 type locality were it not that the Wisconsin drift at that point 

 may not include the Shelbyville or earliest Wisconsin sheet of 

 till. The same objection may be urged against buried soils 

 found in Kane, De Kalb, La Salle, and Bureau counties, for in 

 all these counties the outer Wisconsin ridge appears to be the 

 Bloomington moraine, and the limits of the Shelbyville may be 

 to the east of this ridge. It has seemed advisable, therefore, in 

 the selection of a type locality to pass to central Illinois, where 

 the Shelbyville sheet extends beyond the later sheets of Wis- 

 consin drift. This, unfortunately, carries us beyond the lowan 

 till, but the loess, whose deposition seems to mark the close of 

 the lowan glaciation is there well developed. The interval 

 between the loess and Shelbyville till sheet probably marks as 



'For abstract of paper see Proc. A. A. A. S., 57th meeting, 1888, pp. 183-184. 



