OUT WASH FROM THE OLDEST DRIFT. 239 



more, and he thinks the gravel extends to the stream level. Pebbles of 

 granite 2 to 2^ inches in diameter, collected by Wheeler on this terrace, 

 were inspected by the writer. 



From the available data it appears that the stream along the Tionesta 

 had sufficient strength to carry gravel down nearly if not quite to the Alle- 

 gheny Valley. Possibly a large filling occurred, which has since been 

 almost entirely removed. In support of this view the deposit at Newtown 

 Mills may be cited. The amount of channeling in the gravel near the 

 bend of the Tionesta also indicates that considerable material was carried 

 down the Tionesta. 



LOWER ALLEGHENY VALLEY. 



The Upper Allegheny, as above noted, appears to have had points of 

 special filling, as at Tidioute and near Oil City, between which were long- 

 stretches in which the amount of filling may have been less. Upon turning 

 to the Lower Allegheny a very different condition is found. The valley 

 there has been filled up with sand and gravel to an even grade, harmonizing 

 in slope with that of the present stream, but 250 feet or more above it. 

 Below the mouth of the Clarion the Allegheny has a well-defined ancient 

 gradation plain, which has been trenched by the river to a depth of 200 

 feet or more, as indicated in Chapter III. The gravel covers this old 

 gradation plain to an average depth of perhaps 80 feet. In places it 

 extends 50 to 100 feet below the gradation plain, as if either that amount 

 of trenching of the old valley floor had preceded the gravel deposition or a 

 secondary filling had taken place during a subsequent excavation. But, as 

 alread}^ shown (Chapter III), the trenching appears not to have been com- 

 pleted until an interglacial stage subsequent to this early gravel deposition. 



From the mouth of the Clarion up to the point where the glacial 

 boundary bears away from the Allegheny (near Kennerdell) the Allegheny 

 Valley is very narrow, being about the width of the inner valley below the 

 mouth of the Clarion. It carries only occasional remnants of gravel out- 

 wash, yet it can scarcely be doubted that there was a filling to correspond 

 with that on the Lower AUeg'heny. Some of the remnants stand at a suf- 

 ficiently high altitude to clearly support this view. 



Since the deposition of the gravel so much erosion has occm-red on the 

 gradation plain of the Lower Allegheny that the original surface of the gravel 

 is preserved in only a few places. In several places the gravel deposits 



