SURFACE GEOLOGY. 4A5 
era. So far as I have observed, the work done by the Drift agency itself 
in sculpturing the 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 tue 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 rock 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 ®btained 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 
