DRAINAGE OF THE GLACIAL PERIOD. 323 



The high level gravel terraces so constantly lining 

 the water-courses in the Middle and Western States, and 

 which formerly were attributed to the advance into these 

 regions of the waters of the ocean, are readily accounted for 

 by the action of the torrents set free by the melting of the 

 ice during the closing years of the great Ice age. One of the 

 striking confirmations of the glacial theory appears in the 

 absence of terraces in the valleys of such minor streams as 

 have their sources south of the glacial limits. For example, 

 in Ohio the small streams in the southeastern part of the 

 State, whose sources are outside of the glacial limits, present 

 a marked contrast to the other streams of the State flowing 

 south, as do also the streams flowing to the north and empty- 

 ing into Lake Erie. The troughs of the Wabash, the two 

 Miamis, the Scioto, the Hocking, and the Muskingum, with 

 their tributaries, are all lined by gravel terraces, rising from 

 fifty to one hundred and fifty feet above the present flood- 

 plains, showing the enormous volume of the streams which 

 flowed through them at the close of the period. The coarse- 

 ness of the material in these terraces also bears witness to the 

 violence of the currents. But between the mouth of the 

 Muskingum, at Marietta, and the mouth of the Little Beaver, 

 the streams entering the Ohio are devoid of terraces, the ex- 

 planation being that their sources lie outside of the glaciated 

 limit, so that they had access neither to the accumulations of 

 the glacial deposits, which furnished material for the terraces, 

 nor to the floods of water that distributed it. To the east- 

 ward, again, upon striking the streams whose drainage-basins 

 lie within the glaciated limit, high terraces, containing north- 

 ern pebbles brought from beyond the water-shed, begin again 

 to appear, both along the margins of the streams in the gla- 

 ciated area, and also through their whole course below the 

 boundary. In the matter of terraces, likewise, the northern 

 tributaries of the Ohio are in stinking contrast with the 

 southern. 



East of the Alleghanies the same contrast appears between 

 the streams rising within the glaciated area and those outside 



