6QQ GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



north along- the valleys some distance farther than on the intervening- ridges, 

 g-iving the appearance of spurs. They are perhaps the lines of subglacial 

 drainage, many of the knolls being gravelly and a few having the form of 

 eskers. 



The interlobate portion of this morainic system in western Wyoming 

 County presents in its southern part a very sharp knob-and-basin topography, 

 scarcely an acre of the surface being plane. The knolls rise usually but 20 

 to 30 feet above the basins, and there are many very small, sharp hummocks 

 only 5 to 10 feet in height. Upon passing north-ward in the interlobate 

 belt the knolls become more scattering and among them are areas of 

 considerable extent -svhich have a nearly plane surface. The knolls are, 

 ho-wever, in some cases rather large, some of them being 40 to 50 feet in 

 height. 



The portion of this morainic system bet-ween the interlobate tract and 

 the Grenesee River also presents a sharp knob-and-basin topography, with 

 knolls 10 to 30 feet or more in height inclosing numerous small basins. 

 There is some tendency to aggregation in belts that trend northwest to 

 southeast in line with the trend of the system, but this tendency is scarcely 

 so marked as in the district west of the interlobate tract. There are also 

 strips a mile or so in width in the midst of this system in which knolls are 

 rather rare. These suggest intermorainic tracts, but they are not continued 

 far enough to cause a separation of the system into distinct moraines. 



STRUCTURE OF THE DRIFT. 



In the gently undulating morainic ridges from Euclid, Ohio, eastward 

 into Pennsylvania there is a clayey till similar to that found in the plains 

 farther west, and but few gravel knolls occur. The coarse material becomes 

 more conspicuous as the moraine rises along the escarpment in Erie County, 

 Pa., and Chautauqua County, N. Y., while on some of the high ridges 

 farther east the stones are so abundant as to give the moraine a gravelly 

 appearance. The outer belt in the valley-like depressions at the head of 

 Lake Chautauqua and at Cassadaga and Bear lakes carries a more clayey 

 till than the inner or main belt. There is also a very clayey till in the old 

 Upper Allegheny or Conewango Valley and the old course of South Catta- 

 ra-ngus Creek. But from the crossing of Cattaraugus Creek near Collins 

 Center eastward to the interlobate moraine the till is very stony and gravel 



