OLD UPPER ALLEGHENY DRAINAGE SYSTEM. 129 



which enters the Allegheny at Irvineton. It continues narrow as far as the 

 mouth of the Clarion River, being in places scarcely one-fourth mile, and 

 rarely exceeding one-half mile, in width. In this narrow portion there are 

 occasional remnants of the fluvial plain of the small predecessor of the 

 middle portion of the Allegheny, which, as indicated below, discharged 

 northwestward along French Creek (reversed), and eventually reached the 

 Lake Erie Basin. 



At the mouth of Clarion River a broad gradation plain comes in from 

 that valley and continues down the Allegheny to its mouth. This has been 

 trenched to a depth of about 200 feet below the level of the old rock floor. 

 The trench or inner valley is usually about one-half mile in width, though 

 it increases to nearly a mile near the mouth of the stream. At the level of 

 the gradation plain there is a general width of about 1 mile. This grada- 

 tion plain is capped by a deposit of sand and gravel, with an average thick- 

 ness of perhaps 40 feet, that serves to accentuate the terrace-like appearance, 

 for it fills up small trenches that had been cut in the gradation plain prior 

 to the gravel filling. It is scarcely necessary to state that above the level 

 of this gradation plain the bluffs are far more worn and receding than in 

 the inner or canyon valley lying below it. 



OLD UPPER ALLEGHENY DRAINAGE SYSTEM. 



Evidence that the upper portion of the Allegheny drainage basin for- 

 merly discharged northwestward to the Lake Erie Basin was presented by 

 Carll some twenty years ago.^ He called attention to the constriction of 

 the present valley near Kinzua, Pa., and noted that the rock floor of the 

 valley slopes northward or in the reverse direction from the present stream 

 from this point to the mouth of Cold Spring Creek, where it is met by a 

 a rock floor sloping with the present stream. He also noted a broad 

 valley deeply filled with diift leading westward from the mouth of Cold 

 Spring Creek to the headwater portion of Conewango Creek. Having no 

 opportunity to examine the divide at the head of Conewango Creek, he 

 suggested an outlet to the Lake Erie Basin along the rather broad valley 

 of Cassadaga Creek, a tributary of the Conewango. In this .suggestion he 

 seems to have been in error, for a much broader valley leads northward 

 across the low divide between Conewango and Cattaraugus creeks, and 



^ Second Geol. Survey Pennsylvania, Rept. P, 1880, pp. 1-10, 330-439. 

 JION XLI 9 



