POSTGLACIAL BIOTA OF THE GREAT LAKES REGION 183 



Wisconsin loess, however, is very scanty when compared with the great loess 

 deposits of the interglacial intervals. 



A. IOWA 



In Clay and Obrien counties, northwest Iowa, on the edge of the early 

 Wisconsin till, loess occurs and varies from several inches to some feet in thick- 

 ness. No mollusks are reported. 218 



B. ILLINOIS 



The early Wisconsin drift bordering the Illinois River from Peoria to Henne- 

 pin received a partial covering of loess. 219 This loess mantle has an average 

 thickness of 2 to 6 feet, and in some places attains a thickness of 10 to 14 feet. 

 The bulk of the thicker deposits is a buff-colored calcareous silt, often contain- 

 ing lime concretions and the shells of mollusks, thus closely resembling the loess 

 of Iowa. The weathered surface is brown and is leached to a depth of from 2 

 to 4 feet. No lists of the particular species contained in these deposits has 

 been seen. Near Palos Park, Cook County, a loess deposit occurs but no fos- 

 sils have been observed. 220 



C. WISCONSIN 



Loess deposits of late Wisconsin age have been reported from Wisconsin 

 by Prof. Salisbury. 221 Near Green Lake, Green Lake County, about two miles 

 northeast of the village of Dartford, the loess rests on Wisconsin drift and 

 is 150-200 feet above Green Lake. This loess contains no fossils, but at the 

 west end of the lake, in section 4, on a slope at a lower level, facing the lake, the 

 loess contains both concretions and gastropod shells. The character of the mol- 

 lusks is not stated and no list is given. Near Devil's Lake, loess occurs, but 

 without evidences of life. 



At Ablemans, eight miles west of the Wisconsin moraine, in a ravine tribu- 

 tary to the Baraboo River, the loess is rich in concretions and gastropod shells. 

 The bones of a small animal were also found 10 feet below the top of the loess. 

 At Logansville the clay in the valley is somewhat loess-like, is distinctly strati- 

 fied, and contains shells. 222 This deposit is probably not true loess, but silt 

 formed by streams. 



218 Geol. Surv. Iowa, XI, p. 485. 



218 Barrows, HI. State Geol. Surv., Bull. 15, p. 48. 



220 Personal communication from Dr. W. W. Atwood. 



221 Journ. Geol, IV, pp. 929-937, 1896. 

 m Salisbury, op. cit., p. 934. 



