177 



of mammals are found. The color varies from yellow to almost white, 

 due probably to modified forms of the same material. The thickness varies 

 from a thin coating to twenty-five feet or more. Where exposures of 

 the loess material occur the faces are vertical and compact, and any 

 markings upon the face remains well preserved indefinitely. (See photo- 

 graph of exposures along Wabash River north of Old Fort Knox, Knox 

 County.) How far the material from the lowan drift extends under the 

 Wisconsin is not known. 



The Wisconsin Stage. — Considerable time elapsed between the main 

 deposition of loess and the invasion of the Wisconsin ice sheet. This 

 time is designated as the Peorian Stage. Erosion produced many changes 

 in the surface of the loe.ss and the underlymg drift. In places extensive 

 deposits of muck and iteat have been found. Following the Peorian Stage 

 there occurred one of the most important stages of glaciation in the en- 

 tire glacial period. "It is marked by heavier deposits of drift than those 

 made at any other invasion. Throughout much of its southern boundary in 

 the United States, a prominent ridge of drift is to be seen rising in places 

 to a height of 100 feet or more above the outlying districts on the south, 

 and merging into plains of drift on the north, which are nearly as elevated 

 as its cx'est. 



"The southern border of this drift sheet is less conspicuous in In- 

 diana than in the States to the east and west. The ridge on its southern 

 border in western Indiana rises scarcely twenty feet above the outer 

 border tract, and it is no more conspicuous in central Indiana. Indeed, 

 from near Greencastle to the vicinity of Columlnis there is not a well 

 defined ridging of drift along the border, the limits there being determined 

 by the concealment of the loess beneath a thin sheet of bouldery drift. 

 From the east border of p]ast White River a few miles below Columbus, 

 northeastwai-d to Whitewater Valley at Alpine, in southern Fayette County, 

 there is a sharply defined ridge of drift standing twenty feet to forty 

 feet above outer border tracts. Upon crossing Whitewater where the 

 border leads southeastward, it is not so well defined as west of the river, 

 though there is usually a ridge about twenty feet in height." 



Thickness of the Drift. — "There are surprising differences in the 

 thickness of the drift within the State. The portion of the older drift 

 exposed to view has, as already noted, an average of about thirty feet. 

 The additional 100 feet of the newer drift is, however, deposited very 



[12— 29034[ 



