l62 



THE POPULAR SCIENCE MONTHLY. 



of gravel in tlie old rock gorge is connected with the Glacial 

 period is clearly shown by the fact that these lower terraces can 

 be followed up the banks of every stream which comes out of the 

 glaciated region to the old ice border, where they emerge into the 

 moraines which were deposited directly by the ice. This is shown 

 in our map, on which a small portion of the glaciated area ap- 

 pears with Big Beaver and Little Beaver Creeks flowing out from 

 it. The gravel terraces at Brilliant and Steubenville are shown 



10 30 



Fig. 4. Map of Middle Ohio Eivee Kegion. 

 Glaciated area, shaded. Terraces shown by dots. 



on this, together with other remnants of this terrace farther up 

 the river. 



Only those streams which rise in the glaciated area have such 

 terraces. The contrast between the Monongahela and the Alle- 

 ghany in this respect is very marked. The Alleghany River 

 throughout its course was gorged with this glacial gravel, but 

 the Monongahela River neither had the gravel within reach nor 

 the floods of water coming from the melting ice to distribute it if 

 it had been within reach, therefore the gravel terraces are absent. 



