UPPER OHIO DRAINAGE SYSTEM. 95 



mainly to the southern end. of the Beaver Valley, since the gradation plain 

 there is but little obscured by glacial deposits, though the interpretation of 

 northward drainage was extended to the Lake Erie Basin by way of the 

 Mahoning and Grand River valleys, and was applied to the rock floor beneath 

 the present stream as well as to the high-level terraces. Soon after the 

 publication of this paper the present writer discussed the nature of the 

 evidence and dissented from that part of the interpretation which assigned a 

 northward drainage for the channels that are buried beneath the present 

 streams,"^ while admitting the force of the evidence of the high terraces in 

 favor of northward drainage. 



In a paper prepared in 1894, Chamberlin and Leverett^ discussed this 

 outlet, together with other featru'es in the Upper Ohio region. The evidence 

 was thought to favor a northward discharge through the Beaver prior to 

 the excavation of the deep trench in which the lower portion of the river 

 now flows, but the interpretation of northward drainage through bui-ied 

 channels was shown to be incorrect. ' 



Two years later I. C. White discussed this outlet in connection with a 

 paper on the terrace deposits of the Monongahela River; he considered it a 

 "pretty surely established" line of discharge; but, like Chambei'lin and 

 Leverett, he restricted the northward discharge to a time previous to the 

 opening of the deep trenches of that region.' 



Turning to the Beaver outlet, we find that a gradation plain a mile 

 or more in average width extends the whole length of the Beaver River 

 and descends northward from about 870 feet at the mouth to about 810 feet 

 at the head of the river, or a fall of 60 feet in a distance of 25 miles in the 

 reverse direction from the jDi'esent flow of the stream. From the head of 

 the Beaver, at the junction of the Mahoning and Shenango rivers, the grada- 

 tion plain does not maintain so great a breadth, on either the Mahoning or 

 the Shenango, as that presented by the Beaver. On the Mahoning, which is 

 the line of continuation suggested by Spencer and adopted l)y Foshay, the 

 breadth is reduced near the Pennsylvania-Ohio line to less than one-third 

 of a mile, and the bordering uplands there become very prominent, with 

 an altitude of about 400 feet above the river. On the Shenango there is a 



1 Am. Jour. Sci., 3d series, Vol. XLII, 1891, pp. 200-212. 



^ Idem, Vol. XLVII, 1894, pp. 247-283. 



" Am. Geologist, Vol. XVIII, pp. 368-379, December, 1896. 



