744 



THE POPULAR SCIENCE MONTHLY 



of the glaciers that the river began the task of cutting a new 

 channel for itself the one it now occupies; but when the ice 

 reached and crossed the channel and entered Kentucky, this partly 



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made new way was likewise obstructed. As a result the water rose 

 higher and higher, backing farther and farther up its valley, until 

 its estimated depth varied from three hundred to six hundred feet. 



