matured /l&frades, 



on. Before the ice age there was supposed to 

 be no connection between Lake Michigan and 

 Lake Huron, as there is now, through the 

 Straits of Mackinac. 



Another preglacial river had its rise in the 

 region of Lake Huron and flowed through an 

 old river bed extending from the Georgian 

 Bay in a southeasterly direction through the 

 province of Ontario, and emptied into the 

 present Lake Ontario. From Lake Ontario 

 there is an old river bed running through the 

 Valley of the Mohawk which empties into the 

 Hudson at Troy. Neither of these two rivers, 

 having their sources in the north, found an 

 outlet through the present St. Lawrence 

 River. During the time of the glacial period 

 there is evidence that there was more than one 

 center of snow and ice accumulation and each 

 of these great centers probably had several 

 subcenters. This theory has color given to it 

 by the directions of movement shown by the 

 glacial drift. 



The rounded appearance of bowlders was 

 caused by the grinding action of the ice. 

 These bowlders, when they were first torn from 

 their rocky beds by the irresistible power of 

 ice pressure, were rough and jagged in shape, 

 the same as any rock would be, torn from a 

 quarry by a blast They have been smoothed 

 and rounded by rubbing against the moving 

 ice and against each other in the progress of 



