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- 
nées 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. 
InrerGLactaL Prriops. 
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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