212 



G. F. WRIGHT— AGE OF DON RIVER GLACIAL DEPOSITS 



seem unwarranted to draw any sweeping conclusion from their occurrence 

 in the lower part of the fluviatile beds overlying the lowest till. 



Figure 3. — Map of North American Pleistocene Ice-sheet at its maximum Extension 



Showing the approximate southern limit of glaciation, the three main centers of ice 

 accumulation, and the driftless area within the glaciated region. (United States Geo- 

 logical Survey.) 



The Labrador later than the Keewatin Glacier 



In discussing inter- Glacial epochs and their time ratios it would seem 

 that too little attention has been paid to the evidence that in America 

 the glacial movement from the Keewatin center preceded that from 

 Labrador. How far east the early movement of the Keewatin ice-sheet 

 extended it is impossible with our present knowledge to tell with cer- 

 tainty; but Lake Superior copper has been found in the glacial deposits 

 in Columbus, Ohio, and still farther north and east in Medina County, 



