THE LAST Ol THIL GLACIAL LAKES 



shore of Lake Huron, at Riclimondville on the western shore, 

 at Standisli near Sai;inaw Bay, and near Manistee on the east- 

 ern Lake Michigan shore, are at the same elevation, thus 

 estabhshing the position of the Algonquin hinge line north of 

 which the land has uptilted. At times uplift was slow and 

 steady so that the beaches were actually split while forming, 

 and several beaches of the lowering lake actually come to- 

 gether at a common point — just to add to the complexities. 



The records made along the eastern boundary of the glacier 

 during Lake Algonquin time have not been fully worked out; 

 but when the ice sheet in the St. Lawrence valley had re- 

 treated to the northern edge of the Adirondack Mountains, 

 a new outlet for Lake Iroquois somewhat lower than that at 

 Rome, New York, was found, and a channel was scoured 

 along the northern mountain slope toward Lake Champlain. 

 Continental uplift shortened the life of this stage, which is 

 known as Lake Frontenac. 



When the ice barrier withdrew farther north the land was 

 so low that the sea, which had gradually risen with the return 

 to it of vast quantities of glacial waters, entered the valley of 

 the St. Lawrence (as earlier it had entered the valley of the 

 Hudson), filling the Ontario basin with ocean water, 

 as is shown by the remains of marine or salt-water animals left 

 in the deposits. This marine embayment has been named 

 Gilbert Gulf. 



As it must come to everything, an end came to Lake Al- 

 gonquin. The barrier holding it to the highest level finally 

 gave way when the ice retreated north of North Bay, On- 

 tario, and opened an outlet even lower than the Kirkfield 

 outlet. Then through a short river bordering the ice front the 

 waters of the upper lakes poured into the marine gulf which 

 had flooded the valleys of the St. Lawrence and Ottawa rivers, 

 of Lake Champlain and Hudson River. This great marine 

 estuary is known as the Champlain Sea. Evidence is lacking to 

 determine the time duration of this, the Ottawa, stage of the 



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