213 MAN AND THE GLACIAL PERIOD. 



connection with the Glacial period there was a subsidence 

 of the whole region to an extent of 1,100 feet. 



The principal objection heretofore alleged against this 

 supposition is that there are not corresponding signs of 

 still- water action at the same level on the other side of the 

 Alleghany Mountains. This will certainly be fatal to the 

 subsidence theory, if it proves true. But it is possible that 

 sufficient search for such marks has not yet been made on 

 the eastern side of the mountains. 



The other theory to account for the facts is, that the 

 terraces adduced in proof of the Cincinnati ice-dam were 

 left by the streams in the slow process of lowering their 

 beds from their former high levels. This is the view 

 advocated by President T. C. Chamberlin. But the fresh- 

 ness of the leaves and fragments of wood, such as were 

 noted by Professor White at Morgantown, and the great 

 extent of fine silt occasionally resting upon the summits 

 of the water-sheds, as described above, near Clarksburg, 

 bear strongly against it. Furthermore, to account for the 

 terrace described at Bellevue, which contains Canadian 

 pebbles, President Chamberlin is compelled to connect 

 the deposit with his hypothetical first Glacial epoch, and 

 to assume that all the erosion of the Alleghany and 

 Monougahela Rivers, and indeed of the whole trough of 

 the Ohio River, took place in the interval between the 

 " first " and the " second " Glacial periods (for he would 

 connect the glacial deposits upon the south side of the 

 river at Cincinnati with the first Glacial epoch) — all of 

 which, it would seem, is an unnecessary demand upon the 

 forces of Nature, when the facts are so easily accounted for 

 by the simple supposition of the dam at Cincinnati.* 



* See matter discussed more at length in the lee Age, pp. 326- 

 350, 480-500 ; Bulletin of the United States Geological Survey, No. 

 58, pp. 76-100 ; Popular Science Monthly, vol. xlv, pp. 184-199. Per 

 contra, Mr. Frank Leverett, in American Geologist, vol. x, pp. 18-24. 



