REVIEW OF GEOLOGICAL STKTCTUEE. 29 



by wells and borings. They had at no time bods of uniform depth and slope, the softer 

 rock strata over which tliey fl jwed being more readily eroded than the harder. From 

 this cause there would be pools separated by ripples or water-falls. • « » 

 The harder rocks were where the ancient rapids or falls are now sometimes seen, and 

 constitute the present bed rook 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 : 



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," uo'harder rock appearing 

 except near the lock at the east end. ' ' * 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 rook, but at the west end no rock is fuund 

 to a depth of eighty feet. At Windsor the dam is built on soapstone bottom, no rock, 

 t. 9 , hard rock, appearing except near the lock. At McContelsvilie the dam is built 

 upon a soft, shelly rook. At Hokeby 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 w'Jjich projected into the old valleys, as the Ohio 

 does at Louisville, (as described on p. 14 of Vol. II, Geolopjy 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 fact.=< gathered by the writer — chiefly from the borings 

 for oil in the valleys of our western rivers — prove that the buried chan- 



