242 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



view that the occurreuce of the gravel at low levels can not, in some cases 

 at least, be accounted for by creeping or by landslides ; but since a stream 

 is liable in such places to redeposit material on its inner curve during the 

 deepening of the valley, the writer considers it probable that the gravel 

 has been carried by the river to lower levels than its original position. The 

 original depth can as jet scarcely be determined on its own inherent evi- 

 dence, and the precise extent of the excavation in that part of the valley 

 prior to the gravel deposition may be regarded as uncertain, except as 

 correlated conditions tln*ow light upon it. 



Opposite the n:iouth of the Clarion, on the west side of the Allegheny, 

 there is a recess in the valley wall which carries a deep and extensive 

 deposit of gravel, with an upper limit about 275 feet above the river. 

 There is probably an area of 80 acres with an average depth of 100 feet 

 of gravel. Across it there passes an old channel of the river whose bed 

 is about 250 feet above the present stream. Just east of it is another flat- 

 topped terrace, apparently a reduction from the higher terrace, with an 

 altitude scarcely 200 feet above the river. In both terraces the pebbles are 

 fine, mainly an inch or less in diameter, and include a very few Canadian 

 rocks. 



From tliis recess on the west side the stream appears to have passed 

 eastward across the Allegheny Valley and filled the valley to about the 

 level of an oxbow-like channel east of Parker, brought to notice by Chance.^ 

 This so-called oxbow, however, stands somewhat higher than the broad 

 gradation plain of the Clarion-Lower Allegheny, and has a channel much 

 narrower than that of neighboring portions of the valleys of these streams. 

 The view that it is an old oxbow of either of these streams has recently been 

 called in question by E. H. Williams^ and an alternative view suggested. 

 This later view is one which the writer considers more consistent with the 

 features than the one presented by Chance. It refers the opening of the 

 double channel resembling the forks of an oxbow to a shifting of a small 

 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. 

 At the time of the gravel deposition under consideration, this small oxbow- 

 like channel became partially filled; but, as noted by Wright,^ there was not 



'H. M. Chance: Second Geol. Survey Pennsylvania, Kept. V^ 1880, pp. 17-22. 

 " At Albany meeting of Geological Society of America, Dec. , 1900. 

 'Am. Jour. Sci., 3d series, Vol. XLVII, 1894, pp. 173-175. 



