GEOLOGY OF THE TORONTO REGION 



The hills of Archaean rocks to the north of the 

 Palaeozoic beds were powerfully scoured on the 

 northeastern (stoss) side, showing roches mouton- 

 nees forms, but the lee side is often rugged and more 

 or less covered with boulder clay or loose erratic 

 blocks. 



Some have supposed that the basins of the lakes 

 were largely hollowed by the continental ice sheets, 

 but it is improbable that any important amount of 

 excavation was accomplished in this way. The dam- 

 ming of valleys by morainic materials was far more 

 important and no doubt gave rise to the innumerable 

 rocky lakes of the Archaean region to the north. 



The heaping up of a great interlobate morainic 

 mass between the valleys of Lake Ontario and Lake 

 Huron blocked the channel of the ancient Laurentian 

 River and deflected the waters round the southwest- 

 ern peninsula of Ontario into Lake Erie and the 

 Niagara River, thus changing the whole arrangement 

 of land and water. 



This land of irregular morainic ridges may be 

 followed from a point near Trenton to Aurora, north 

 of Toronto, and then to the top of the escarpment 

 toward the west; while less conspicuous loops sur- 

 round the southwestern end of the Ontario basin. 



INTERGLACIAI, PERIODS. 



Between the sheets of boulder clay there are beds 

 of stratified sand and clay evidently formed by water, 

 and hence interglacial. The earliest of these inter- 

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