SURFACE GEOLOGY. 445 



era. So far as I have observed, the work done by the Drift agency itself 

 in sculpturing tbe rock surfaces of Ohio has been almost infinitessimally 

 small. With the valley of the Ohio River and its tributaries on the 

 southern slope of the State before tne Drift era as now, and with the 

 great northern depression, or valley, now filled by Lake Erie, and the 

 streams draining the northern slope into it as now, there was little for 

 the Drift forces to do except to scatter over an old surface its various ma- 

 terials of clays, bowlders, etc. Doubtless wherever there were rock sur- 

 faces exposed, these forces, whatever they may have been, acted as a file 

 or sand-paper upon wood already carved, to smooth down many of the 

 minor asperities, and the tool-marks remain at various points on the 

 smoothed or striated rocks. 



The larger streams in the Second District had at some time antecedent 

 to the Drift era large portions of their beds deeper than now, as shown 

 by wells and borings. They had at no time beds of uniform depth and 

 slope, the softer rook strata over which they flowed being more readily 

 eroded than the harder. From this cause there would be formed pools 

 separated by ripples or waterfalls. The ancient pools are now filled with 

 alluvial materials, excepting where we find the Drift clay, and the latter, 

 so far as I have observed, seldom, if ever, rests directly upon the bed-rock, 

 but upon sand or gravel. The harder rocks were where the ancient 

 rapids or falls are now sometimes seen, and constitute the present bed- 

 rock of the streams. The Ohio River now flows upon a solid rock floor 

 at Letart Falls, in Meigs county, and such bed-rocks are reported by the 

 United States engineers, who have carefully investigated the Ohio River 

 with reference to the improvement of its navigation. Similar rock beds 

 are found in the Muskingum and Hocking rivers. The following facts 

 have been obtained through the courtesy of E W. Sprague, Esq., of Low- 

 ell, Washington county, who was connected with the construction of the 

 slack-water improvement of the Muskingum River : " At Marietta, at 

 the east end of the dam, the solid rock was found twenty-four feet below 

 the low-water mark, but no rock at all was found under the western two- 

 thirds of the dam. At Devol's the dam is built on ' red soap-stone,' no 

 harder rock appearing, except near the lock at the east end." This soap- 

 stone is a common red clay shale found in the upper Coal Measures. At 

 Lowell the dam is "on rock, but when we go above or below, the rock 

 disappears on one side of the river or the other." At Beverly "the dam 

 at the east end is built on rock, but at the west end no rock is found to 

 the depth of sixty feet." " At Luke Chute the lock and east end of dam 

 are built on rock, but at the west end no rock is found to the depth of 

 eighty feet." " At Windsor the dam is built on soap-stone bottom, no 



