NATURAL HISTORY, TORONTO REGION 



grey clay, due to the grinding up of grey shales ; but 

 it becomes red or brown where the underlying rock is 

 of that colour, e.g., over the Queenston shale, showing 

 how local the source of the clay has been. 



There are at least five sheets of boulder clay of 

 different ages exposed in the vicinity of Toronto, but 

 in most other parts of the lake 'region only one or two 

 are to be found. The oldest tills are harder and more 

 resistant to weathering than the later ones. The 

 latest sheet is considered to have been formed by the 

 Wisconsin ice sheet of American geologists. The 

 oldest may be Pre-Kansan. It has not been possible 

 to separate these till sheets with any certainty up 

 to the present, except at Scarborough Heights, where 

 almost the whole series is displayed. 



The ice which covered the region came from the 

 Labrador centre, but did not pass, as might have 

 been expected, southwards or southwestwards across 

 the country, since the valleys of the present Great 

 Lakes deflected it into more westward directions. 

 The ice followed these wide and deep depressions as 

 great lobes, which were confluent when the glaciation 

 was at its maximum, but which separated again 

 when the ice sheets began to wane. 



The ice sheets, after passing through the Ontario 

 valley, spread out towards its western end and then 

 climbed the escarpment, leaving polished and striated 

 surfaces on the Niagara limestone beyond the cliffs. 

 Striae and even deep gouges and grooves were left 

 on the Devonian limestones around Lake Erie. 

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