DRAINAGE OF THE GLACIAL PERIOD. 329 



sheet. The floods characterizing that period had access to 

 an unlimited amount of material, which was easily swept into 

 the current, and rolled down the torrential bed toward the 

 Ohio River. Upon reaching the Ohio, the combined cur- 

 rent of the two streams in the larger valley would have far 

 less power of transportation than the constricted current in 

 the channel <>f the glacial tributary. The bowlders would, 

 therefore, be deposited at the mouth of the Beaver, where it 

 joins the Ohio, and, owing to the influence of the current of 

 the Ohio itself, would be carried below the junction of the 

 two rivers. Hence it is that we find so many glacial bowl- 

 ders below the junction, and so few above it. The accumu- 

 lation of a terrace of an equal height above the junction, but 

 consisting of fine and local material, is also what would be 

 required by theory as well as what is found to be the case in 

 fact. Thus we have, in this single instance, one of the best 

 possible verifications of the glacial hypothesis. 



Of the glacial terraces on the Delaware River, from the 

 Water-Gap to Trenton, N*. J., there will be occasion to speak 

 more fully when treating of the subject of man's relation 

 to the Ice age in North America. Nor can we more than 

 allude to those which line the Mohawk and the troughs of the 

 Hudson and its tributaries. It is sufficient to say that the 

 passengers upon the New York Central Railroad can satisfy 

 themselves of the existence of these terraces east of Little 

 Falls, N. Y., and between Schenectady and Albany, by 

 merely looking out of the car- windows toward the north ; 

 and a moment's reflection upon the topography of the coun- 

 try will show that the terraces of the Mohawk and the up- 

 per Hudson are much more recent than those of the Susque- 

 hanna and the Delaware, since glacial streams could not have 

 occupied the Mohawk until after the ice-front had retreated 

 from northeastern Pennsylvania and the highlands of south- 

 ern New York, in which the drainage-basins of the Susque- 

 hanna and the Delaware River are situated. When, there- 

 fore, the glacial floods of the Mohawk were at their height, 

 the Delaware and the Susquehanna had been relieved of 



