LOWER OHIO DRAINAGE SYSTEM. 117 



locality (the Illinoian drift). This abandoned course, unlike the abandoned 

 coiirse of the Middle Ohio from Wheelersburg- to Waverly, was cut down 

 before its abandonment to a level below that of the present Ohio. It corre- 

 sponds apparently to the trenches or canyon valleys of the Middle and 

 Upper Ohio systems. The rock floor of the valley being below the level of 

 the present drainage lines, its slopes can be determined only by means of 

 borings. From the data thus obtained along the abandoned course, as well 

 as along the Ohio below the mouth of the Great Miami, it appears that the 

 rock floor lies about 60 feet below the present low-water level of the Ohio, 

 and has a descent in the present direction of drainage. From a level about 

 375 feet above tide at Cincinnati it falls to 360 feet or less at Rising- 

 Sun, Ind., and to 350 feet or less at the mouth of the Kentucky River. At 

 Cincinnati the tests have been sufliciently numerous to show the full depth 

 where the old Licking crossed the present Ohio. At other points the tests 

 are not so numerous, biit they are sufficient to show that the altitude of the 

 rock floor becomes lower below the mouth of the Great Miami than it is at 

 Cincinnati. Borings in the abandoned channel between Cincinnati and 

 Hamilton show a rock floor as low as those in Cincinliati. So far as the 

 writer is aware, no borings along the Great Miami above Hamilton have 

 reached so low a level before entering rock as those on the Ohio below the 

 mouth of the Great Miami. 



In addition to the slope of the rock floor, there is the further evidence 

 for the route suggested by James, in the presence of a broader valley along 

 that line than on the Miami northward from Hamilton. The latter becomes 

 reduced just above Hamilton to a width of less than a mile, and that, too, 

 at a height of fully 200 feet above the level of the rock floor, and its 

 general width as far up as Dayton is but little more than a mile. The 

 abandoned valley leading west from Hamilton, in the route suggested by 

 James, is IJ to 2 miles in width, and there is no constricted place from 

 there to the Ohio, nor down the Ohio to the mouth of the Kentucky. In 

 this connection it may be remarked that constrictions farther down the 

 Ohio near Madison, Ind., and Leavenworth, Ind., occur in the passage 

 through escarpments of resistant rocks, where the valley has exceptionally 

 high blufl^s, and apparently do not lessen the size of the valley more than 

 would naturally result from the greater resistance of the rock strata. 



The earlier paper presented by Fowke is accompanied by a map which 



