34 



TWELFTH REPORT. 



The lake has two well defined beaches ditfei-ing about 20 feet in level. 

 These beaches have suffered differential uplift in the S^aginaw basin and 

 on the northern j^art of the east slojje of the Thumb, and also in the 

 eastern part of the Lake Erie basin, but elsewhere thev are horizontal. 

 In the horizontal portion the higher beach stands about 6S0 feet above 

 sea level or 100 feet above Lakes Huron and Michigan and the lower one 

 about 6G0 feet above sea level. In western New York the higher beach 

 reaches an elevation of 880 feet, or 200 feet above the horizontal portion. 



Transit ionaJ Jakes. (Grassniere and Elkton heaches). As the ice 

 border shrank into the Ontario basin jjassages were opened for the dis- 



Fig. 7. Lake Algomiiiin and Lake Ironuois, with probable con-elative ice border. Numerals 

 and isobases indicate altitude above sea level of the highest beach of these lakes. 

 Isobases of Michigan and Huron ba^in.s by Taylor and Goldthwaite. 



charge of the waters of Lake AA\arren eastward past Syracuse, New 

 York, to the Mohawk valley, at altitudes low enough to draw down the 

 lake level and cause the abandonment of the Grand River Outlet. The 

 ultimate discharge by the new route was to the Atlantic Ocean at 

 New York instead of to the Gulf of Mexico. Two weak beaches were 

 formed in southeastern Michigaxi, known as the Grassmere and the 

 Elkton, at levels 20 and 40 feet respectively below the level of the lower 

 of the two beaches of Lake Warren. AVhile full tracing has not yet been 

 made around the entire course from Michigan to New York it seems 

 probable that these beaches are to be correlated with two of the eastern 

 outlets, past Syracuse. 



