OLD MIDDLE ALLEGHENY DRAINAGE SYSTEM. 



135 



sion, and sustains such relations as to show clearly that it has suffered no dis- 

 turbance since deposition. The shelves, therefore, antedate the gravel, and 

 are remnants of an old river bottom. The hill standing between the old chan- 

 nel and the present river (see PI. VIII) seems to have been detached from the 

 bluff south of the river. This change was probably brought about at the 

 time the valley became filled greatly with glacial gravel, the amount of filling 

 being sufficient to raise the stream 



above the level of the old neck that 

 joined the hill to the south bluff. 



Following the supposed out- 

 let northwestwai'd, there is an old 

 meandering valley lying near the 

 present French Creek and in part 

 coinciding with it (see fig. 5). On 

 a small eastern tributary of this old 

 valley 3 miles northwest of Frank- 

 lin, wells situated a mile or more 

 back from the junction of the trib- 

 utary with the old valley strike a 

 rock floor at about 1,040 feet above 

 tide, which is about as low a level 

 as the rock floor found in one of 

 the wells in the Franklin oxbow, 

 and is within 25 feet of the bottom 

 of the other. These wells pene- 

 trate about 100 feet of drift of 

 early glacial age. As they are 

 back from the principal valley, the 

 presumption is that the main channel is lower. Farther northwest along the 

 valley, at a point 8 miles from the Allegheny, a well is found which reaches 

 the rockfloor at 1,025 feet above tide — i. e , at a depth intermediate between, 

 the depths of the two wells in the abandoned oxbow at Franklin. This well 

 is situated near the southern edge of the valley and can scarcely be sup- 

 posed to have struck its deepest portion. Again, in an old oxbow 3 miles 

 north of Utica, similar in every way to the oxbow at Franklin except that 

 it lies within the limits of the Wisconsin ice invasion, the floor is shown by 



Fig. 6. — Provable preglacial drainage of part of the Middle 

 Allegheny drainage basin. 



