WISCONSIN DRIFT BOEDER. 79 



feet below the top of the hill. In Parke County the altitude is close to 700 feet, but in northwest- 

 ern Vigo, near Wabash River, it is not much above 600 feet. 



CHARACTER. 



From Wayne County, Inch, south westward to the valley of East White River below Colum- 

 bus, a distance of 75 miles, and for a width of 6 or 8 miles, the surface of the border is gently 

 undulating. Few of the knolls or swells are more than 15 or 20 feet in height, and thej may 

 not average more than 10 feet, but they are so numerous and occupy so large a part of the sur- 

 face as to put this border in decided contrast with the flat tract on its inner or western edge as 

 well as with the plain of older drift on its outer. 



West of East White River the knolls are in few places closely aggregated and most of them 

 are small, like those east of the river. For 2 or 3 miles in southeastern Putnam County the 

 border is marked by a low ridge standing 20 to 25 feet above the outer border plain. A con- 

 siderable part of the border from there northwest to the Wabash Valley in Parke County shows 

 closer grouping of the knolls, many of which are 10 to 20 feet in height. 



STRUCTURE OF THE DRIFT. 



CONTRAST WITH OUTLYING DRIFT. 



The drift of the Wisconsin border in Indiana, though feeble in morainic expression and 

 slight in relief above the outer border district, in structure contrasts strikingly with the out- 

 lying drift. Being relatively thin, in most places measuring but 10 to 20 feet, it may be com- 

 pared at numerous points with the underlying drift. Indeed, few regions afford so good an 

 opportunity for contrasting the Illinoian and Wisconsin drift sheets. 



The outlying district shows a weathered till sheet capped by a thin deposit of light-colored 

 pebbleless silt or white clay, generally but 3 to 5 feet in depth. The same weathered till sheet 

 in places capped by its silt is exposed beneath the Wisconsin drift in numerous ravines. 



WEATHERING. 



The weathering of the surface of the Wisconsin drift sheet is decidedly less than that of the 

 upper part of the Illinoian drift buried beneath it. In the Wisconsin drift small pieces of lime- 

 stone are still present at the surface, but in the Illinoian they have been dissolved or leached 

 out by percolating waters to a depth usually of several feet. The weathered portion of the 

 Illinoian is a darker brown than the Wisconsin, and is tinged with red, apparently by the high 

 oxidation of the iron. This tinge is rarely found in the Wisconsin drift surface. The Illinoian 

 till has become partly cemented by the deposition apparently of calcareous and ferruginous 

 material through the agency of percolating waters, but the Wisconsin seldom shows cementa- 

 tion. In consequence of this cementation it is much more difficult to excavate the Illinoian 

 than the Wisconsin till. Cementation of itself is not everywhere a proof of the great age of the 

 till, but where the lower drift sheet is cemented and the upper uncemented it corroborates other 

 evidence to that effect. Moreover, this partly cemented lower drift can be traced continuously 

 from beneath the newer drift into the outer border district and is found to be about equally 

 cemented in both situations. This proves that the cementing material was not derived from 

 the overlying Wisconsin drift, and that cementation was probably largely effected before the 

 deposition of the latter. 



BURIED SOIL. 



The presence of a buried soil under the Wisconsin drift is a matter of common observation, 

 not only along the Wisconsin drift border but throughout the northern half of Indiana and in 

 neighboring States. In Elrod's report on Decatur County 1 the following statements appear: 



The black soil bed is generally present where the bowlder clay and the yellow clay form a junction. It has never 

 been reported as occurring in or under the blue bowlder clay 2 or its equivalent, the white clay of the "flat woods." 



' Twelfth Ann. Rept. Indiana Dept. Geology and Nat. Hist., 18S2, p. 142. 

 2 Probably the partly cemented blue bowlder clay of Illinoian age. 



