. Glacial formations and drainage features of the Erie and Ohio basins. d with early glacialgravel (see PI. VIII), one boring reached rock at 1,040 feet above tide,and another penetrated to a level only 1,015 feet above tide without reach-ing rock. The gravel at these points rises to a level much above that of theterraces connected with the outer moraine of the Wisconsin or late ice inva- FlG. 5.—Present drainage of part ot the Middle Alleghenydrainage system. See Carll: Second Geol. Survey Pennsylvania, Bept. !?, p. 334. OLD MIDDLE ALLEGHENY DRAINAGE SYSTEM. 135 siou, and sustains such relati
. Glacial formations and drainage features of the Erie and Ohio basins. d with early glacialgravel (see PI. VIII), one boring reached rock at 1,040 feet above tide,and another penetrated to a level only 1,015 feet above tide without reach-ing rock. The gravel at these points rises to a level much above that of theterraces connected with the outer moraine of the Wisconsin or late ice inva- FlG. 5.—Present drainage of part ot the Middle Alleghenydrainage system. See Carll: Second Geol. Survey Pennsylvania, Bept. !?, p. 334. OLD MIDDLE ALLEGHENY DRAINAGE SYSTEM. 135 siou, and sustains such relations as to show clearly that it has suiTered no dis-turbance since deposition. The shelves, therefore, antedate the gravel, andare remnants of an old river bottom. The hill standing between the old chan-nel and the present river (see PL VIII) seems to have been detached from thebluff south of the river. ! change was probably brought about at thetime the valley became filled greatly with glacial gravel, the amount of fillingbeing sufficient to raise the stream. above the level of the old neck thatjoined the hill to the south bluff. Following the supposed out-let northwestward, there is an oldmeandering valley lying near thepresent French Creek and in partcoinciding with it (see fig. 5). Ona small eastern tributary of this oldvalley 3 miles northwest of Frank-lin, wells situated a mile or moreback from the junction of the trib-utary with the old valley strike arock floor at about 1,040 feet abovetide, which is about as low a levelas the rock floor found in one ofthe wells in the Franklin oxbow,and is within feet of the bottomof the other. These wells pene-trate about 100 feet of drift ofearly glacial age. As they areback from the principal valley, thepresumption is that the main channel is lower. Farther northwest along thevalley, at a point 8 miles from^ the Allegheny, a well is found which reachesthe rock floor at 1,025 feet above tide—i. e, at a depth intermediate
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