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REVIEW OF GEOLOGICAL STRICTURE. 29 
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 pools separated by ripples or water-falls. i hy ie 
The harder rocks were where the ancient rapids or falls are now sometimes seen, and 
constitute the present bed rock of the streams. 
He then cites a number of instances where the Ohio River shows a 
rock bed apparently extending quite across the present stream, and quotes 
from E W. Sprague, Esq., the following facts in regard to the construc- 
tion of the dams on the Muskingum: 4 
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 soapstone,” no harder rock appearing 
except near the lock at the east end. : i Me 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 a depth of eighty feet. At Windsor the dam is built on soapstone bottom, no. rock, 
, hard rock, appearing except near the lock. At McConrelsville the dam is built 
upon a soft, shelly rock. At Rokeby no rock was found, and the dam is built upon a 
sand foundation. At Taylorsville the dam is built upon the bed rock of the river. At 
Zanesville the dam is upon bed rock. At Symmes Creek the dam and lock are upon 
soapstone at the east end, but no rock was found at the west end within a depth of 
sixty feet. 
These facts would, at first sight, seem to refute the theory that the 
Muskingum and Ohio at one time flowed in continuous channels at a 
much lower level than now. They will be seen to be in entire harmony — 
with it, however, when it is explained that the present streams: do not 
follow the exact lines of the old filled up channels, but in many places 
cross spurs or shoulders which projected into the old valleys, as the Ohio 
does at Louisville, (as described on p. 14 of Vol. II, Geology of Ohio). 
By reference to Mr. Sprague’s notes, it will be seen that some of the 
Muskingum dams were built on the solid rock which formed the side of 
the channel, in others the dams were built partly on the rock and partly 
over the old channel, where the rock was not reached at the depth of 
sixty or eighty feet. In one instance, at Rokeby, the dam was constructed 
directly over the old channel and no rock was found. 
The valleys of the Ohio and all its principal tributaries, after being 
deeply excavated, were filled with gravel and sand—by the setting back 
of water into them, and the checking of their currents—to a much higher 
evel than that of the present streams. This old filling has now been 
\partially and irregularly removed, leaving terraces and broad bottom 
lands, under which the old channels are frequently concealed. An im- 
mense number of facts gathered by the writer—chiefly from the borings 
for oil in the valleys of our western rivers—prove that the buried chan- 
