RATE OF FALL OF OHIO RIVER. 83 



2.25 miles. Below the rapids, in the 367 miles to its mouth, the fall of the 

 stream is but 3 inches per mile. 



In addition to the Louisville Rapids there are several other rapids 

 where the stream makes a descent of a few feet over rock. But these rock 

 rapids appear, in most if not all cases, to be simply shelves on the border of 

 channels which extend below the river bed. Through a partial filling of 

 the valley with glacial gravel and sand the stream has been directed across 

 the shelves or rock points on its borders. In the case of the' Louisville 

 Rapids an old channel has been traced past their south border through 

 the city of Louisville.^ At Letart Falls, a few miles above Pomeroy, 

 Ohio, where there are rock rapids with about 3 feet descent, it is found by 

 well data that the rock drops off toward the Ohio side of the valley to a 

 level 25 feet or more below the low-water surface of the stream. Similar 

 conditions are found at Cincinnati, Gallipolis, and Steubenville, Ohio; 

 Parkersburg and Ravenswood, W. Va.; and Rising Sun, Ind. 



The river bed presents an interesting series of shoals and riffles, sepa- 

 rated by pools in which the water is deeper and the fall very low. The 

 summary of the profile made by the army engineers shows 187 pools with 

 a depth of more than 7 feet at low water, which occupy 632.5 miles, an 

 average of 3.47 miles to each pool. In these pools the rate of fall is in 

 some cases less than 1 inch per mile, thoug-h the usual descent is about 2 

 inches. At the riffles the descent seldom exceeds 2 feet per mile, but at 

 Deadmans Riffle, 14 miles below Pittsburg, a descent of 4.41 feet is made 

 in 0.65 mile; and at Letart Falls a descent of 3.2 feet is made within a 

 mile; while at the rapids at Louisville there is, as above noted, a descent of 

 23.09 feet in 2.25 miles. 



The depth of the rock floor of the Ohio beneath the level of the 

 present stream is generally between 30 and 60 feet, though there are points 

 in the lower course where it is known to reach 75 feet. Although several 

 rock formations, which differ greatly in their power to resist stream corra- 

 sion, are encountered in its course from Pittsburg to Cairo, the eff^eet on 

 the giadient of the stream is scarcely appreciable. It appears that the 

 2jresent Ohio Valley had become sufficiently mature at the time of the 



' Data on this channel were furnished the writer by Prof. William J. Davis, of the Louisville 

 school board, and by ilessrs. John Ryan and John C. Oestrich,'of the Louisville Pump Works. Data 

 collected by C. E. Siebenthal suggest another channel north of Jeffersonville, Indiana. See Eept. 

 Geol. Survey Indiana for 1900, pp. 359-364. 



