PRE-II.LINOIAN Till. IX SOUTHERN ILIIXOIS 



13 



materials shown in Table II. This shows a total of 13.2 per cent of foreign 

 material. 



It is not known definitely how thick the lower till is, but about 200 yards 

 north of the exposure, a well at about the same elevation as the base of the 

 cut penetrated 31 feet before encountering bed rock. 



INTERPRETATION 



The upper loess, while not fossiliferous in this place, bears such rela- 

 tions to the Illinoian drift that it is believed to be of early Peorian age. The 

 Illinoian drift in its three phases, i.e., gumbotil, leached till, and fresh till, is 

 normal and typical of the area. 



Since the pre-Illinois loess formation was thoroughly leached prior to 

 the invasion of the Illinoian ice, it must be notablv older. And since it must 



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% 





-X- 





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Fie. 4. — Photograph of jointing in lower till 



have taken a long time to leach 15 feet of loess, assuming it to have been 

 originally calcareous, a probable assumption in the case of loess, this forma- 

 tion seems to be associated with a pre-Illinoian glacial invasion — quite pos- 

 sibly the Kansan — as the early Peorian and early Wisconsin loesses are 

 associated concomitantly with the late phases of the Iowan and early Wis- 

 consin ice invasions, respectively. It could scarcely be associated in age or 

 origin with the underlying till for it is separated therefrom by the gumbotil, 

 and it is clearly not related to the gumbotil. 



The lower till and gumbotil must be either Kansan or Nebraskan. Its 

 relations to the leached gray loess above show that it is vastly older than the 

 loess, for it was deposited, weathered to gumbotil. and much of its upper 

 surface eroded prior to the formation of the loess. It seems best, there- 



