100 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



Tuniing now to the bordering uplands, we find another hne of evidence 

 favoring- reversal. Immediately above its junction with the Clarion the 

 Allegheny cuts through an elevated tract which to the eastward constitutes the 

 divide between waters flowing north and northwest into the Allegheny and 

 those flowing south into the Clarion, while to the westward it constitutes the 

 divide between the northward or eastward flowing tributaries of the Allegheny 

 and the streams flowing south and west to the Beaver and the Shenango (see 

 fig. 5, p. 135). The high divide is broken by a gap scarcely a mile wide and 

 500 to 600 feet in depth where crossed by the Allegheny. The altitude 

 and relief of this divide appear to be due to its relation to draiiiage systems 

 rather than to axes of upheaval, for its trend is in large part independent of 

 such axes. That is to say, it constitutes a natural boundary between the 

 Middle Allegheny and the Clarion-Lower Allegheny drainage basins. 



The slope of rock shelves and remnants of gradation plains north from 

 the supposed divide bring further coijfirmation of the hypothesis of reversal. 

 The rock shelves which stand 375 to 400 feet above the present stream, or 

 1,275 to 1,300 feet above tide, near the supposed divide, show a decline of 

 about 200 feet in the 20 miles northward to the mouth of French Creek. 

 This rate of fall would be natural only in a small stream descending from 

 an elevated table-land. 



The combined force of all the lines of evidence is such that there 

 seems no doubt that there was formerly a divide on the line of the Allegheny 

 ust above the mouth of the Clarion separating the drainage of the old 

 Monongahela system from that of the old Middle Allegheny system. 



MIDDLE OHIO OR OLD KANAWHA SYSTEM. 



Near the eastern border of the flat-topped crest of the Cincinnati arch 

 the streams in the vicinity of the Ohio River have a trend which strongly 

 suggests the former presence of a divide. Those to the east of the arch trend 

 up the present Ohio toward the mouth of the Scioto, while those on the flat 

 crest, from its very eastern border, lead westward down the Ohio. The posi- 

 tion of the old divide at the border of the present Ohio seems to be very near 

 the village of Manchester, Ohio. The valley of the Ohio presents higher 

 blufts in the vicinity of the supposed divide than at points above and below, 

 and the general topographic expi-ession seems adapted to the occurrence of 

 a divide at the place suggested. To this is added the evidence from an 

 abandoned northward outlet, discussed below. 



