GEOLOGY OF THE TORONTO REGION 



thus far no deposits formed in these interglacial 

 lakes, except perhaps near Toronto, have been iden- 

 tified. Each retreat of the ice must also have been 

 followed up by bodies of water whose outlet was 

 blocked toward the east. The last ice retreat, that 

 of the Wisconsin sheet, has left unmistakable evi- 

 dence of a succession of glacial lakes which covered 

 much of the region. Of these lakes two are of 

 greatest importance Lake Iroquois, which occupied 

 the basin of Lake Ontario, but at a higher level ; and 

 Lake Algonquin, which covered most of the great 

 upper lakes with a single vast sheet of water. 



These ancient lakes have been somewhat carefully 

 mapped, and their shores are as mature and often 

 almost as well preserved as those of the present 

 Great Lakes, though now, of course, covered with 

 vegetation. 



LAKE IBOQUOIS. 



The shores of Lake Iroquois, with their wave-cut 

 cliffs and well-defined gravel bars, have been traced 

 almost all round Lake Ontario, by Gilbert and Fair- 

 child in New York, and by Spencer and Coleman in 

 Ontario; but there is a wide gap at the north-east 

 end of the basin, where no shore has been found. 

 The shore in that quarter was of ice. Since the 

 St. Lawrence outlet was blocked, Lake Iroquois 

 emptied through the Mohawk Valley in New York 

 into the Hudson. The beach is continuous except 

 where cut by river valleys and at Scarborough 

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