526 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



of Powell, and less conspicuously on the Cleveland, Akron and Columbus 

 and the branches of the Big Four Railroad. Field studies show that what 

 is true of the points where railroads cross is true all along the moraine. 

 The abrupt outer border makes it one of the most plainly marked moraines 

 yet traced. There is, in many places, a rise of 20 feet in 100 yards in 

 passing from the plain into the moraine, and in the portion south of Mount 

 Gilead a rise of 35 feet is made in 100 to 150 yards, the moraine rising up 

 like a bluff on the west side of Walnut Creek. 



TOPOGRAPHY. 



While the moraine is a conspicuous topographic feature when separated 

 from other moraines, it becomes obscure when blended with them, for its 

 constituent knolls lack sharp contours, such as characterize the knolls of 

 the main morainic system. As a rule it presents gentle swells 10 to 15 feet 

 or even less in height, covering 2 to 5 acres each. The surface is properly 

 termed undulating and contrasts strikingly with the plane-surfaced tract 

 on the outer boi'der. It has not such contrast with the inner border tract, 

 there being instead a transition from the decidedly undulatory, through 

 gentle waves, to the nearly plane; but there is not on the inner border 

 disti'ict quite so level a tract as on the outer. 



THICKNESS AND STRUGTUKE OF DRIFT. 



So far as yet shown by well borings the drift does not present great 

 variations in thickness, such as have been found to characterize the earlier 

 moraines. The floor upon which it rests, though composed of several 

 distinct kinds of rock, seems to be remarkably free from such inequalities 

 as are common in the hilly districts bordering the basin. It is quite 

 probable, however, that the basin is traversed by valleys which are filled 

 with diift, but a general inspection of the surface does not reveal their 

 position. The large streams have extensive rock exposures where they 

 cross the moraine and also north and south of it. From these exposures 

 and the knowledge obtainable from well records it is thought that the 

 thickness of drift generally falls between 50 and 100 feet, but that it is 

 less than 50 feet in the elevated part of the eastern limb and the extreme 

 northern part of the western limb. 



Natural exposures and wells ahke show that the amount of assorted 

 material is very small. The till, which constitutes the great bulk of the 



