444 ' FRANK COLLINS BAKER 



there are, in addition to the silt, the heavy deposits of Wisconsin drift, which 

 have buried the soil and weathered zone to such a depth that it is rarely exposed. 

 However, a few exposures have been found in the deeper valleys, and wells not 

 infrequently penetrate both the silt and soil under the Wisconsin drift (1902, 

 p. 292). 



On another page the same author says : 



In fact, the great majority of buried soils reported in Ohio, Indiana, and 

 Illinois appear to be at this horizon (p. 293). 



The shells in the deposit under discussion are not from one of 

 these old soil horizons. They represent, probably, material that 

 was washed down from flood plains farther upstream, where they 

 had been deposited during periods of flood previous to the advance 

 of the Wisconsin ice cap. The fact that the shells are found from 

 just beneath the surface to the lowest strata accessible, as described 

 by Mr. Fluck, indicates that the burying of the shells occurred 

 more or less continuously during the deposition of the valley deposit. 



What relation the Peorian interval may bear to these shells is 

 not at present known, the lowan invasion apparently not notably 

 affecting this territory so far east of the area of this drift. The 

 mollusks might have Hved during Peorian time and then been 

 buried by the Wisconsin deposits. As the land fauna is so nearly 

 like that of deposits farther south, which are referred to the Sanga- 

 mon interval by Leverett, it seems best to refer the Flat Rock shells 

 to the same horizon. At Lawrenceburg, near the Ohio-Indiana 

 Hne, old soils (forest beds) containing shells are found. Some 

 years ago Mr. A. C. Billups (1902, p. 50) listed many species of 

 land mollusks from the deposits along the Ohio River near Law- 

 renceburg. These are listed in Table III for comparison with the 

 Flat Rock shells, which are also shown in this table. It will be 

 noted that the two faunas are substantially the same. The differ- 

 ence is only what we would find in comparing the recent faunas of 

 two more or less widely separated areas. It would appear, there- 

 fore, that the reference of the Flat Rock River shells to the Sanga- 

 mon interval is well supported by the geological as well as faunal 

 evidences. 



Many deposits in the valleys of streams that formed drainage 

 channels from the Wisconsin ice sheets probably contain the remains 



