BORDER OF THE ILLINOIAN DRIFT, 257 



tain a central knoll rising to a height of 75 to 100 feet, around which are 

 smaller ones ; in other cases there are chains of knolls, and occasionally an 

 isolated knoll appears. The Ohio Valley itself carries several clusters of 

 knolls between Vevay, Ind., and the mouth of the Grreat Miami at the Ohio- 

 Indiana State line. More commonly the drift accumulations in the Ohio 

 Valley have a level top like a terrace and stand 150 to 200 feet above the 

 river. It should not be inferred, however, that this level-topped drift filling 

 represents a fluvial terrace, for it appears to be the product of the ice 

 sheet, just as in the case of level-topped drift surfaces on the uplands. It 

 consists largely of till or of poorly assorted material and is very unequal 

 in amount in different parts of the valley. Occasionally it fills the valley 

 to a height of 150 to 200 feet above low water, while in other places there 

 appears to have been much less filling. 



Near Carrollton, Ky., a definite drift ridge appears between the Ohio 

 and Kentucky rivers, apparently at the extreme limits of glaciation, which, 

 not only because of its position but also because of its contours, may be 

 classed as a moraine. The highest points stand nearly 200 feet above the 

 Ohio River, but the low parts of the crest are scarcely 125 feet above that 

 stream. On either side of it are terraces of the Ohio and Kentucky rivers, 

 standing about 90 feet above the streams. The ridge is scarcely a half mile 

 in width and consequently rises sharply above the terraces. It leads 

 directly east across a gap in the rock ridge between the two rivers. This 

 drift ridge consists largely of till and carries many striated stones. The 

 question whether it may be a reduction by erosion from a drift filling with 

 level top, such as appears at intervals farther up the Ohio, was considered 

 by the writer while on the ground, but it seemed that the contours are better 

 explained as the product of drift deposition than of drainage erosion. From 

 the eastern end of this di'ift ridge the drift border rises to an upland tract 

 with an altitude more than 300 feet above the Ohio. On this upland, which 

 is greatly dissected by valleys and ravines, the drift forms a conspicuous 

 deposit along the ravines that discharge northward to the Ohio, but there 

 is a very meager deposit on the ravines that lead southward to Eagle 

 Creek, a feature which is to be expected where the glacial boundary lies 

 near the divide. 



For a few miles up the river from Vevay, level-topped remnants of a 

 drift filling appear at an altitude about 150 feet above the river. They are 



MON XLI 17 



