116 LIFE OF THE PLEISTOCENE 



4. Closing Transition Stage. At its end Lake Algonquin appears to have 

 been held up by a small glacial barrier, at some point in the Ottawa Valley east 

 of Mattawa. When this last dam was removed the waters rushed eastward 

 thru the Ottawa, Petawawa, and Madawaska valleys to the Champlain Sea and 

 came to a settled level in the upper lake basin only when the eastward flowing 

 outlet had been established on the coll at North Bay (Taylor). The discharge 

 from Port Huron was abandoned at this time (Plate LIII). 



J. NIPISSING GREAT LAKES (Plate LIII) 



At this time the ice sheet had disappeared from the Great Lakes region 

 and did not act as a barrier. The entire discharge was into the Champlain 

 Sea via the North Bay outlet. These lakes differed but little in outline from 

 those of today. Differential up'lift in the North Bay region soon caused the 

 abandonment of the North Bay outlet which was shifted to Port Huron and 

 Chicago, the waters backing up at these localities. For a time both the North 

 Bay outlet and the Port Huron outlet were active and a transition or two outlet 

 stage ensued. Later, the Chicago outlet took the place of the North Bay outlet 

 but this was abandoned when the Port Huron waters had cut down the outlet, 

 and the present Great Lakes resulted, the Chicago outlet being left as a marsh. 

 The Nipissing beach is one of the strongest of the old lake beaches and has 

 been traced entirely around the Great Lakes. Before reaching its present 

 level, the Great Lakes constructed other beaches, one, known as the Algoma 

 (seen at Algoma Mills, Ontario) is 35 feet below the Nipissing beach and 50 feet 

 above Lake Huron. Other minor transition beaches are known. 



K. THE CHAMPLAIN SUBSTAGE (Plates LII, L'H) 



During the latter part of the Port Huron stage of Lake Algonquin, the land 

 was notably depressed in the eastern part of the territory and became partly 

 submerged by an arm of the sea which filled part of the Lake Ontario basin, 

 extending up the Ottawa Valley past the city of Ottawa and also occupying 

 the Lake Champlain basin, and extending down the Hudson River Valley to 

 the sea at New York. The old shore lines now stand at elevations of from 400 

 to 625 feet above the present sea level. The New England states and a portion 

 of Canada formed an island surrounded by salt water. At this time the east- 

 ern outlet was lower than either the Chicago or St. Clair outlets and the lake 

 was somewhat smaller than at present in both the Michigan and Huron basins. 

 This condition did not last for a great length of time and subsequent uplift 

 caused the sea to recede and the outlet to be transferred again to the St. Clair 

 River and the five Great Lakes assumed their present form, with the outlet 

 thru the St. Clair and St. Lawrence rivers. 



