78 PLEISTOCENE OF INDIANA AND MICHIGAN. 



The margin of the Wisconsin drift is easily traced through Decatur and Jennings counties 

 by the soil as well as by the topography. The drift area is termed by the residents "black 

 land," whereas the silt-covered outer border district is termed "white clay," "crawfish land," 

 or "slash land." For more than 40 miles in Fayette, Decatur, and Jennings counties the border 

 is so sharp and distinct that it can be located wit hin a few yards. This abrupt change was 

 early pointed out by Elrod, who recognized in a measure its relation to or dependence on glacial 

 events. 1 The line of separation is very regular, passing without deviation over hills and valleys, 

 showing but a rough adaptation to the contours, and giving positive evidence of glacial as opposed 

 to glacio-natant drift deposition. 



MORAINAL TRACT WEST OF EAST WHITE RIVER. 



West of the East White Valley the Wisconsin border is less striking topographically. 

 Instead of a ridge with continuous relief it presents only low swells and short ridges, few of which 

 are more than 10 feet in height, and in many places they are scattered and inconspicuous. 

 The contrast in soil is also less striking as a rule than it is east of the East White River, for the 

 margin of the Wisconsin drift sheet is so thin and in places has so much silt or white clay incor- 

 porated with it that such occurrences can be identified only by close examination. In places 

 the presence of pebbles alone serves to distinguish it from the white clay or surface silt of the 

 outer border district. The admixture of silt, however, is conspicuous for only a mile or two 

 back from the Wisconsin border, the till farther back being of a normal fresh type. And even 

 in places where a large amount of the white clay has been incorporated with the Wisconsin till 

 sufficient calcareous material is present to produce a richer soil than that of the white clay 

 district. In addition to the contrast in soil the Wisconsin drift border is marked by surface 

 bowlders of all sizes up to several feet in diameter. Outside the Wisconsin border the white 

 clay has buried the bowlders of the IUinoian till sheet to a depth of several feet. 



The course of East White River from Taylorsville to Columbus, a distance of 8 miles, was 

 determined apparently by the Wisconsin ice invasion, for the stream is now flowing in a narrow 

 valley just outside the Wisconsin drift border and not in the broad old valley once occupied by 

 a preglacial and presumably by an interglacial predecessor that lies a short distance inside the 

 border. The present stream cuts across the lower ends of tributaries of old streams, which are 

 traceable eastward to the broad valley by sags or depressions. 



ALTITUDE. 



The altitude of the Wisconsin drift border within the State of Indiana has a range of more 

 than 500 feet. In the vicinity of the reentrant angle between the Miami and East White lobes 

 an altitude of fully 1,150 feet is found. From the high points in western Fayette County 

 southwestward to McCoy station in Decatur County the general altitude of the border is between 

 1,000 and 1,100 feet. Southwestward from McCoy it descends continuously from 1,026 feet to 

 891 feet at Letts Corners and 645 feet at Elizabethtown. Along East White River the altitude 

 is between 630 and 720 feet, the latter height being reached near Tajdorsville. Between East 

 White and White rivers few, if any, altitudes exceed S50 feet, though neighboring hills just 

 outside the border rise above 900 feet. In the valley of White River the altitude is less than 

 650 feet. West of White River, between Brooklyn and Monrovia, the border skirts an elevated 

 tract which in places rises to about 950 feet, but the Wisconsin drift itself is nowhere found 

 above 850 feet. The altitude declines to about 750 feet at Mill Creek on the line of Morgan and 

 Putnam counties. In Putnam County it fluctuates nearly 200 feet in- crossing the ridges and 

 valleys, or from 900 to 700 feet. A prominent hill south of Greencastle, though surrounded 

 by Wisconsin drift, seems not to have been overridden, for the upper 50 feet carries a deposit of 

 white clay, as on ridges outside the limits of the Wisconsin drift. The upper limit of the Wis- 

 consin drift there is about 875 feet. The Wisconsin drift extends nearly 3 miles directly south 

 of this hill and fully a mile southwest, and drops to an altitude along the border more than 100 



1 Elrod, Moses, Report on Decatur County: Twelfth Ann. Kept. Indiana Dept. Geology and Nat. Hist., 1882, pp. 140-145. 



