TERILiCES AND VALLEYS IN WESTERN PENNSYLVANIA 153 



bouche into the Allegheny gorge within a mile of one another, 

 and in Glacial time these two valleys were filled by overwash 

 deposits mingled with material from the immediately adjacent 

 slopes." He states also that the rock floor of the abandoned 

 channel is not level, but falls down rapidly toward the river. 

 He does not, however, explain the fact that the col between the 

 heads of the two streams is low and swampy, whereas there is not 

 a case of two large streams rising in an area of swampy ground in 

 the whole unglaciated area of western Pennsylvania, and he says 

 nothing about the broad steep-walled valley through which the 

 small streams flow. 



Frank Leverett (U.S. Geol. Surv. Mon. 41, 242) considers 

 E. H. Williams' view "more consistent with the features than the 

 one presented by Chance," and says further (apparently misinter- 

 preting Williams' view): "It refers the opening of the double 

 channel, resembling the forks of an oxbow, to a shifting of a smaller 

 tributary of the Allegheny from one side to the other of a low hill 

 that stood nearly opposite the point at which the tributary entered 

 the valley." 



■ The data gathered by the writer indicate, first, that the so-called 

 Parker oxbow is an abandoned channel of Allegheny River, and so 

 is properly called an oxbow. The characters which force such a 

 conclusion are: (a) the depression has the size and shape of the 

 Allegheny valley, having a comparatively uniform width of about 

 a mile, and bounding walls from 100 to 300 feet high; (b) the shape 

 is a broad smooth curve with the side of the valley inside the loop 

 gently sloping, and that outside high and steep like the present 

 valley around curves of the river (it resembles, for example, the 

 curve of the Clarion 1 mile south of Turniphole, Foxburg quad- 

 rangle) ; (c) a current with something like the strength of a river 

 must have flowed around the bend, for pebbles up to 6 inches in 

 diameter are found at the most extreme part of the loop. 



Second: The abandoned channel was occupied in a part of 

 Kansan time. The presence of Kansan outwash on the floor, 

 which is at nearly the same elevation as the floor under Kansan 

 material near by, indicates that the last great event before the 

 abandonment of the oxbow was the advance of the Kansan ice 



