Drainage Features of the Upper Ohio Basin. 267 



study of the old and the present rock floors on these tributa- 

 ries leads us to locate an old col near Lowell ville, Ohio, just 

 west of the State line, the altitude of which appears to have 

 been at least 1025 feet A. T. This has been trenched to a 

 depth of about 200 feet, and has a width at bottom of from 80 

 to 100 rods in the narrowest portions. Within this narrow 

 portion, there is a still narrower trench, in places restricted to 

 the limits of the present river channel, a width of but 15 to 20 

 rods. (The greater part of the valley is floored with rock at a 

 level 20 feet or so above the present stream, as shown in sec- 

 tion A, fig. 3). In this inner trench, no borings have reached 

 the depth of those near the mouth of the Mahoning before en- 

 tering rock. Two borings, one at Hazleton and the other a 

 mile east of Struthers, Ohio, enter rock at only 80 and TO feet, 

 respectively, below the present stream. These are 140 to 150 

 feet above the low rock floor, near Edenburg, only nine miles 

 below Struthers. The inner veiy narrow trench is obviously 

 a minor feature in the history of the valley. The main work, 

 after reversal, was the cutting of a trench across the old divide 

 about 200 feet deep and 80 to 100 rods wide in its narrowest 

 parts. The most interesting feature of the lower part of the 

 valley is the sudden descent it makes just above Edenburg. 

 Here the buried floor falls 165 feet in a half mile, as shown by 

 four wells.* The declivity may even be more precipitous as 

 the wells are not so situated as to limit the space occupied in 

 the descent more closely. A mile further down the stream, a 

 well penetrates 200 feet of drift, about 190 feet being below 

 the present river. Farther down stream, so far as there is evi- 

 dence, the rock floor rises, and, in the Beaver gorge near the 

 mouth of the Connoquennessing, is within 52 feet of the bot- 

 tom of the present river, or 90 feet above the deepest portion 

 near Edenburg. Profile A, fig. 3, shows this diagrammati- 

 cally. This profile strongly suggests a fall or steep cascade at 

 Edenburg with a pool below. And this suggestion falls in 

 very happily with the indicated history of the region, which 

 seems to be as follows : 



Before the ice invasion forced the waters of the upper por- 

 tion of the Grand river basin across the divide at Lowellville 

 thereby forming the Mahoning river, a tributary about three 

 miles long descended to the main valley now occupied by the 

 Shenango-Beaver river (then probably occupied by the north- 

 ward flowing Monongahela-Beaver system). This small tribu- 

 tary we think joined the main valley at the horizon of the 

 upper terrace level. At any rate, the drainage of the three- 

 mile valley would be quite incompetent to develop a deep 

 pool. 



* We are indebted to Mr. W. H. Raub of Edenburg for these data. 



