258 Chamberlin and Lever ett — Studies of the 



Franklin, where the stream is supposed to have been largest. 

 In the portion between Franklin and the month of the Clarion 

 the average fall is 2 - 6 feet, of which the greatest fall appears 

 between Franklin and Kennerdell where a col is supposed to 

 have been crossed (the fall there being 4*3 feet, while between 

 Kennerdell and the mouth of the Clarion it is less 'than 1*4 

 feet). Passing now to the portion of the Allegheny between 

 the Brady bend and Pittsburg, where excavation was in the 

 softer strata, there is, in a distance of TO miles, an average fall 

 of about 2*8 feet per mile, or about - 4 feet less than in the por- 

 tion where erosion was in the harder strata. The effect of 

 rock resistance would seem, therefore, to be scarcely appre- 

 ciable when measured by this method and hence inadequate to 

 account for the disparity in the size of the valleys under dis- 

 cussion. 



Furthermore, it is significant that the tributaries of the por- 

 tion of the Allegheny above the mouth, of the Clarion had not 

 deepened their channels to levels in harmony with a grada- 

 tion-plane as low as that of the Clarion. While they. have 

 normal gradients on their upper and middle courses, they de- 

 scend by rapids and cascades to the present Allegheny. This 

 is done from a height of about 400 feet, while the tributaries 

 of the Clarion descend in this way from only about 200 feet. 

 This seems to indicate that they have discharged until recently 

 into a stream which had not reached so low a plane as that of 

 the Clarion. 



Turning now to the bordering uplands, we find a second 

 line of evidence favoring reversal. Immediately above the 

 junction with the Clarion, the Allegheny cuts through an ele- 

 vated tract which to the eastward constitutes the divide be- 

 tween waters flowing north and northwest into the Allegheny 

 and those flowing south into the Clarion, while, to the west- 

 ward, it constitutes the divide between the northward and 

 eastward flowing tributaries of the Allegheny, and the streams 

 flowing south and west to the Beaver and Shenango (see 

 map 4). The high divide is broken by only a narrow gap 

 scarcely a half mile wide and 500 to 600 feet in depth where 

 crossed by the Allegheny. The altitude and relief of this 

 divide appears to be due to its relation to drainage 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 nat- 

 ural boundary between the middle Allegheny and the Clarion - 

 Lower Allegheny drainage basins. 



Before passing to the third line of evidence in support of 

 reversal we should note that the portion of the present Alle- 

 gheny between the supposed col at the mouth of the Clarion 

 and the French creek outlet appears to have been made from 



