DESCRIPTION OF THE OLDEST DRIFT. 231 



an exposure showing the fresh Wisconsin gravel resting on the deeply 

 stained and weathered gravel of the old drift. 



Between Warren and Tidioute there is but a small amount of old drift 

 preserved on the valley borders, and wells in the bottoms indicate that the 

 rock floor is but 25 to 40 feet below the stream. The gravel in the valley 

 bottoms is largely of Wisconsin age. 



In this connection it may be remarked that from Warren down to the 

 mouth of the Allegheny the rock floor is usually within 25 feet of the 

 present stream, and it is not known to lie more than 50 feet below the 

 sti-eam at any point. It thus contrasts strongly with the part of the valley 

 in New York whose rock floor slopes toward the Lake Erie Basin and lies 

 200 to 300 feet or more below the stream. The chief northern tributaries 

 of the Allegheny also have a large amount of drift in their headwater 

 portions and rock floors sloping toward the Lake Erie Basin. These features 

 are discussed in Chapter III. 



At Tidioute there are rock shelves on each side of the Allegheny 

 that carry 80 to 100 feet of old drift, giving the appearance of terraces 

 with an elevation of about 150 feet above the river. The drift appears to 

 be largely g-ravel. A stony drift is found on the slopes of the valley above 

 and also opposite Tidioute up to a height of about 330 feet above the stream, 

 or 1,420 feet above tide, but none was noted at higher levels. Whether the 

 valley was once filled to the upper limit of this drift is not clear. The 

 glacial boundary may extend to the Allegheny at Tidioute. Three miles 

 west of Tidioute, near McGraw post-office, on uplands standing 500 feet or 

 more above the Allegheny, thin deposits of drift occur, and notable deposits 

 occur at about the same distance northwest of Tidioute on the headwaters 

 of East Pine Creek and on Gordon Run. 



At Trunkeyville, on the Allegheny, a few miles below Tidioute, a 

 granite bowlder a foot in diameter was noted on a rock shelf at about 150 

 feet above river level, but no other evidences of glaciation were noted at 

 that place. Possibly it was transported down the valley by the stream, as 

 there are occasional remnants of gravel at levels even higher than the 

 bowlder in that pai't of the valley. At Hickory, the next village below 

 Trankeyville, waterworn pebbles abound on a rock shelf standing about 

 200 feet above the river. 



In the vicinity of the bend near President the Allegheny Valley is 



