274 Chamberlin and. Leveretl — Studies of the 



about 950 feet in a distance of 140 miles. They have been 

 traced down to Toronto, Ohio, where Canadian gravel occurs 

 at the height last named. 



The average thickness of the gravel in this more regular 

 portion is found by combining ten excellent sections to be 83 

 feet; the maximum thickness being 110 feet and the mini- 

 mum 55 feet. This is about double the thickness heretofore 

 given by the senior writer. 



Below this higher sj^stem, thin sheets of gravel occur on the 

 slopes of the valley walls, which might be thought, perhaps, to 

 extend the sections, but which we set aside for consideration 

 later, as they do not seem to us to certainly belong to this 

 series. 



In the irregular portion, several points of special feeding- 

 are recognizable. At Steamburg, New York, the high ter- 

 races slope rather rapidly down the stream, the rate being ten 

 feet per mile. They also slope downward in the opposite 

 direction, i.e., up the stream. As this is also in the portion 

 of the valley whose rock floor descends northward, the drift 

 reaches the great depth of 400 feet. It thins out, however, 

 to a few feet down the river near Kinzua. 



Besides the great accumulations at Clarendon, already men- 

 tioned, there is another special thickening near Reno and Oil 

 City where depths from 100 to 150 feet occur. These are 

 probably referable to the near or immediate presence of the 

 ice edge itself, for the occurrence of foreign drift on the high- 

 lands east of Brandon at 1400 feet A. T., suggests the proba- 

 bility that the ice edge crossed the river there and probably 

 lay near it all the way between this point and Clarendon (see 

 map 1). 



Lower Terraces. — Passing for the moment over intermediate 

 phenomena, we find low in the valleys a series of terraces 

 which conform in general to the slope of the present stream, 

 and usually do not rise more than 50 feet above it, though ex- 

 ceeding this at points of special feeding, as the mouth of the 

 Beaver, where the unusual height of 130 feet is attained. 

 Traced up stream, these terraces are found to head on the 

 outer slopes of the system of terminal moraines before men- 

 tioned, at the points where these cross the respective tributa- 

 ries. The terrace planes graduate into the overwash planes of 

 the moraines and their material graduates into the morainic 

 material itself in a perfectly clear and characteristic way, 

 which leaves no room for doubt respecting their origin. This 

 connection may be seen near Steamburg in the Cool Spring 

 creek valley, near Russellburg on the Conewango, near Chand- 

 ler's valley on Jackson Run, near Wrightsville on the Little 

 Brokenstraw, near Horn's Siding on Big Brokenstraw, near 



