THE PEORIAN SOIL AND WEATHERED ZONE. 187 



LEACHED LOESS BENEATH THE WISCONSIN DRIFT. 



The loess has been traced back in valley exposures several miles 

 beneath the Shelbyville till sheet in northern Tazewell County, Illinois, 

 and beneath the combined Shelbyville and Bloomington sheets in Woodford 

 and Bureau counties. Farther south it has been recognized in well sections 

 in southern Tazewell, northeastern Logan, western Dewitt, southern Macon r 

 and western Sullivan counties, Illinois. The phase known as white clay 

 has been traced several miles up the Kaskaskia and Embarras valleys, in 

 Shelby and Coles counties, beneath the Shelbyville till sheet. 



Of the several exposures in which the loess appears below the Shelby- 

 ville drift, those east of Peoria, in northern Tazewell County, are the best 

 displayed. Decisive evidence is also found at these exposures of an interval 

 of some length between the deposition of the loess and the deposition of 

 the overlying Shelbyville till sheet. In view of these conditions in the 

 vicinity of the city of Peoria, it has seemed appropriate to apply the name 

 Peorian to the interval between the Iowan loess and the Shelbyville till sheet. 



In exposures along the Toledo, Peoria and Western Railway east of 

 Peoria, and also on the east bluff of the Illinois opposite that city, the 

 Shelbyville sheet is underlain by a bed of fossiliferous loess, similar to that 

 found on the surface of the Illinoian outside the limits of the Shelbyville 

 drift sheet, both in texture and in age. The loess is 8 to 12 feet in thick- 

 ness, or about the same as on the uplands outside the Shelbyville sheet. 

 It occurs at a corresponding elevation of about 200 feet above the Illinois 

 River. Beneath it there is exposed fully 100 feet of the older or Illinoian 

 drift sheet. In places the upper part of the loess to a depth of 2 or 3 feet 

 presents a darker brown color than the lower portion and is partially leached 

 of its calcareous ingredients. In one place, about 3 miles west of Wash- 

 ington, a thin soil carrying fragments of wood is exposed in the bluff of 

 Farm Creek at the top of the loess. These exposures east of Peoria were 

 thought to afford excellent opportunities for a comparison of the Peorian 

 and Sangamon weathered zones, and were consequently visited in May, 

 1898, by a party of geologists in company with the writer, including Profs. 

 T. C. Chamberlin, Samuel Calvin, J. A. Udden, Dr. S. W. Beyer, and Dr. 

 H. F. Bain. It seemed to all present that the Sangamon weathered zone 

 calls for more time in its formation than appears to have been required in 



