Geology of Cincinnati. 25 



river has excavated a channel through solid rock for hundreds of 

 miles to a depth of from 500 to 7,000 feet. In places, over 10,000 

 feet of solid strata have been removed over an area of more than 

 five hundred scpiare miles, and all this in an arid region where the 

 rain fall is limited in amount. The region, once an extensive 

 plateau, is now cut up into innumerable canyons and valleys, 

 ramifying in all directions like the veins in a leaf. In a moun- 

 tamous country the corrading powers of water are correspondingly 

 greater, and what was once a smooth mountain side will in time 

 be cut up into ravines innumerable. Capt. Button in his inter- 

 esting account of the Hawaiian Volcanoes* pictures what will re- 

 sult in the course of thousands of years were the forces now in 

 action to continue their work. "As in every other mountainous 

 country," says he, " the ravines would grow wider, their sloping 

 sides would be gradually pared away, and the rocks reduced by 

 secular decay to sand and soil. The silt would be carried off by 

 the running streams to the ocean, and the remnants of the sloping 

 platforms between the ravines would grow narrower until at length 

 they were reduced to knife edges, and would still continue to 

 dwindle in size." Again, he says :t "Whenever a great valley 

 or gorge is eroded in a large mountain mass, the head of the 

 valley forms an amphitheater, or series of amphitheaters, with 

 abrupt or precipitous ravines immediately beneath the peak. In 

 general terms, as we follow such a ravine from the plains below 

 upward toward the summit, the grade of its bed becomes steeper 

 tQ the very last. Again, where two or more mountain gorges de- 

 scending on different sides ^f the cone reach far up toward the 

 summit so that their upper portions are separated only by a narrow 

 divide, then this divide will always be sharp and well preserved 

 through all stages of erosion." 



To give a {q\\ examples of the wearing powers of water in a 

 short time, I will quote a paragraph from Dana.| '' Lyell 

 mentions the case of the Simeto, in Sicily. In two and a half 

 centuries it had excavated a channel fifty to several hundred feet 

 deep, and in some parts forty to fifty feet wide, although the rock 

 is a hard solid basalt. He also describes a gorge made in a deep 

 bed of decomposed rock, three and a half miles west of Milledge- 

 ville, Georgia, that was at first a mud crack a yard deep in which 



*FifthAnr.uaI Report of U. S. Geol. Sur,, p. 213. 

 f Ibid, p. 207. 

 JManual of Geology, p 647. 



