Drainage Features of the Upper Ohio Basin. 273 



on the headwaters of West Hickory creek situated between 

 the above streams. Occasional remnants of gravel deposits on 

 the slopes of the lower courses of these valleys at heights of 

 200 feet or more above the present creek bottom, together 

 with the fact of an open valley to the Allegheny, at least sug- 

 gest the view, if they do not demonstrate it, that these gravel 

 trains were connected with the upper terrace gravels of the 

 Allegheny. 



At Clarendon, there seems ground for believing that the 

 old ice border sent a tongue into the mouth of the old Tio- 

 nesta valley, since it left bowlders on the opposite side of the 

 Allegheny at altitudes 300 feet higher, and the glacial waters 

 built up, with an abrupt north border, the unusual thickness 

 of glacial debris which constitutes the head of the gravel train 

 that follows the modern Tionesta valley. The whole aspect of 

 the deposit is that of a glacial gravel train heading on the edge 

 of the ice. It has the extraordinary height (for a valley train), 

 of 1500 feet A. T. We seem to have, therefore, in this, and in 

 the phenomena on Tidioute, Pit Hole and Hickory creeks, 

 four of the points of origin of the high-level gravel terraces 

 about to be considered. They seem to constitute connecting 

 links between the high terrace gravels and the attenuated drift. 



Terraces. 



From what has already been said respecting the drift border 

 and reversals of drainage, the terrace systems, to which we 

 now turn, would naturally be expected to present much com- 

 plexity of detail, and yet show general systems corresponding 

 to the leading drainage events and glacial incursions. It will, 

 therefore, be convenient to consider the more pronounced sys 

 tems of terraces and then give so much attention as time may 

 permit to minor phases. 



Whatever more there may be, an uppermost and lowermost 

 series of gravel terraces are well characterized. 



The Upper Gravel Terraces. — The upper series of terraces 

 are well developed from the vicinity of Warren, Pennsylvania, 

 to Toronto, Ohio, a distance of 250 miles. They are quite 

 varying in altitude, and in the depth of gravel, on the upper 

 stretches of the Allegheny, where their development was 

 notably influenced by feeders from the adjacent edge of the 

 ice; but in the portion of the valley outside of the imme- 

 diate influence of the ice edge, the series developed into 

 much regularity. The summit altitudes in the upper irregular 

 portion reach from 1200 to 1500 feet A. T. In the lower and 

 more regular portion, the summit heights reach about 1135 

 feet near the mouth of the Clarion, thence descending to 



