260 Chamoerlin and Leverett — Studies of the 



Turning now to the main stream of the supposed old middle 

 Allegheny, we find that the col at Thompson's seems to have 

 had a height of at least 1220 feet A. T. At Tidioute, eight 

 miles below, early glacial gravels rest on a rock shelf (that rep- 

 resents the old river bottom), at 1160 feet A. T. At Reno, 

 a similar shelf stands only 1040 feet A. T., while at Franklin, 

 in an ox-bow filled with early glacial gravel, one boring- 

 reached rock at 1010 feet A. T., while another penetrated to 

 1015 feet A. T. without reaching rock. The gravel at these 

 points rises to a level much above that of the terraces con- 

 nected with the moraine of the later ice invasion 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. Follow- 

 ing along the supposed outlet to the westward, there is an old 

 meandering valley lying near the present French creek and, 

 in part, coinciding with it. (See map 3.) On a small eastern 

 tributary of this old valley three miles northwest of Franklin, 

 wells, situated a mile or more back from the junction of the 

 tributary with the old valley, strike a rock floor at about 1040 

 feet A. T., which is about as low as the rock floor found in 

 one of the wells in the Franklin ox-bow, and is within 25 feet 

 of the bottom of the other. These wells penetrate 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. Continuing northwestward along the valley to a point 

 eight miles from the Allegheny, a well is found which reaches 

 the rock floor at 1025 feet A. T., i. e., at a depth intermediate 

 between the depths of the two wells in the abandoned ox-bow 

 at Franklin. This well is situated near the southern edge of 

 the valley, and can scarcely be supposed to have struck its 

 deepest portion. Farther northwest, in an old ox-bow three 

 miles north of Utica, similar in every way to the ox-bow at 

 Franklin (see map 3), except that it lies within the limits of 

 the later ice invasion, the floor is shown by one well to be 945 

 feet A. T. and by another 960 feet A. T., i. e., 70 feet and 55 

 feet, respectively, below the bottom of the lowest well in the 

 Franklin ox-bow. Still farther northwestward on French 

 creek at Cochranton, Buchanan, and Meadville, there are wells 

 showing excavation to still greater depths ; the first two not 

 reaching the bottom at 915 and 800 feet A. T., respectively, 

 and the last finding rock at 605 feet A. T. The depth of 

 drift at this last point is not less than 4? 5 feet, and the rock 

 bottom is only 32 feet above Lake Erie. Meadville is only 28 

 miles from the Allegheny. To reach this depth on the pres- 

 ent course of the Allegheny it must be followed 150 miles. 



