474 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



moraine indicate that tlie main valleys had suffered a large amount of deep- 

 ening (200 to 300 feet) in the interval between the two ice invasions. 



That much of the so-called "fringe" or sheet of thin drift lying between 

 the Wisconsin morainic system and the glacial boundary is as old as the 

 glacial material on the high-level terraces seems highly probable, since, 

 as stated above, it presents a more aged appearance than that of the Wis- 

 consin system. It also bears a strong resemblance to the attenuated drift 

 border in other regions where the glacial boimdary lies many miles outside 

 the outermost well-defined moraine. 



