GLACIAL DAMS. LAKES, AND WATERFALLS. 383 



junction of streams, and consequently at the mouth of Elk 

 River, on the Great Kanawha, in the vicinity of Charleston, 

 vast numbers of them extend to near 250 feet above this river 

 (800 feet above tide), and scattering ones are found up to 390 

 feet (or 945 feet above tide). Here, along with the hard rocks 

 of local origin, we find great numbers that have come from the 

 Bine Ridge in Virginia and North Carolina, nearly two hun- 

 dred miles distant. 



I shall not be surprised if some of my readers regard this 

 theory of an ice-dam at Cincinnati as visionary ; and, indeed, 

 I do not myself present it as established with the same de- 

 gree of certainty with which the more general facts relating 

 to the Ice age are established. Still, I am confident that 

 close reflection upon the evidence already presented will be 

 sufficient to produce conviction to most minds. The bowl- 

 ders found south of the Ohio River, opposite Cincinnati, are 

 too large to have been carried except by ice, and they are so 

 high above the river, and so far back from it. that floating 

 ice could not have been the agent of transportation, except 

 the channel itself were obstructed. Nor is there any im- 

 probability arising from the nature of the case against such 

 an obstruction by ice. For, through a distance of nearly 

 fifty miles, the ice certainly came down to the northern side 

 of the trough. In much broader valleys than this the ordi- 

 nary ice-gorges during a spring freshet produce remarkable 

 results, raising the water to a great height. But the course 

 of the Ohio at Cincinnati is such as to invite gorges upon the 

 largest scale ; and, with a moving ice-front behind, a perma- 

 nent closure is not improbable. If one should surmise that 

 a depth of five hundred feet of water would lift the ice in 

 the channel so as to secure a subglacial outlet, it should be 

 remembered that the specific gravity of ice is such that it 

 would require more than a depth of six hundred feet of 

 water to lift a body of ice which was seven hundred feet 

 thick ; and the bowlders on the south side of the river are so 

 far distant, the one of w T hich we give a cut being seven or 

 eight miles south of the river, that the ice was doubtless 



