LAKE WAEREN. 257 



of Lake Agassiz, the shores of the Western Superior lake and of Lake 

 Warren show that the departure of the ice was attended by a northward 

 uplift of tlie land.' 



Lake Warren was probably contemporaneous with the maximum ex- 

 tension of Lake Agassiz, and it may have continued until that lake began 

 to outflow northeastward. It belonged to stages in the departure of the 

 ice-sheet which appear to have permitted confluent sheets of water to 

 stretch as a single lake from the western end of the basin of Lake Ontario 

 over the whole or the greater part of the four higher Laurentian lakes. 

 During the glacial retreat from Lake Michigan and the western portion 

 of Lake Erie each of these areas had an outlet to the Mississippi, that of 

 Lake Michigan crossing the height of land close west of Chicago, only 12 

 or 15 feet above the lake and approximately 595 feet above the sea, while 

 the outflow from Lake Erie passed over the lowest point of the watershed 

 between the Maumee and the Wabash, 770 feet above the present sea-level. 

 The departiire of the ice from the southern peninsula of Michigan, how- 

 ever, gave to the glacial Lake Erie, with its extension northward over Lake 

 St. Clair and the southern end of Lake Huron, a lower outlet across the 

 watershed of the Shiawassee and Grand rivers, allowing the Western Erie 

 glacial lake to flow into the glacial Lake Michigan or Warren by a pass 

 whicli is now 729 feet above the sea. Soon after this the further recession 

 of the ice permitted Lake Warren to extend as one level through connect- 

 ing straits from Lakes Ontario and Erie to Lake Superior, discharging its 

 surplus waters by the Chicago outlet. 



Subsequent stages of the glacial, recession, uncovering an outlet from 

 the Lake Ontario basin by Rome to the Mohawk and Hudson, and the 

 history of the Niagara River and of the glacial Lake Ontario or Iroquois, 

 have been ably discussed by Gilbert.^ On a different theory, not recog- 



'The recent explorations of the ancient elevated shore-lines about Lake Superior and the northern 

 parts of Lakes Michigan and Huron by Dr. A. C. Lawson and Mr. F. B. Taylor, the earlier work by 

 Spencer, Gilbert, and others about Georgian Bay and Lakes Erie and Ontario, and the history of the 

 eight distinct large glacial lakes which successively, and in part contemporaneously, occupied the 

 basins of these Laurentian lakes, are reviewed by the present writer, with citations of the somewhat 

 voluminous literature of this subject, in the American Journal of Science (3), Vol. XLIX, pp. 1-18, with 

 map, Jan., 1895. 



= " Changes of level of the Great Lakes," in The Forum, Vol. V, pp. 417-428, June, 1888; and 

 " History of the Niagara River," in Sixth Annual Report of the Commissioners of the State Reserva- 

 tion at Niagara, for 1889, pp. 61-84, with three maps (also in Smithsonian Annual Report, 1890). 

 MON XXV 17 



