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The geological history of the region in Post-glacial times begins with the removal of the remnants of ice which blocked the St. Lawrence outlet, when the water sank from the Iroquois stage to sea level for a time, though the great inflow of fresh water prevented the basin from becoming salt. Meantime, the region to the northeast was slowly rising and at length cut off the basin of Ontario from the Gulf of St. Lawrence, when Lake Ontario came into being. It probably fell far short of its present westward extension at first, but the differential elevation of its outlet at the Thousand Islands has backed up the water, which now stands 246 feet above the sea.



There are many varieties of soil in the district surrounding Toronto, resulting from the events of Pleistocene times just detailed. Residual soils due to the decay of ancient rocks in place scarcely exist in the region, which is almost wholly covered with glacial drift or with old lake deposits. The glacial materials include certain moraines to the north so thickly strewn with stones as to be almost valueless to the farmer, a few kames of barren gravel, and some wide stretches of hopeless outwash sand, all practically useless when stripped of their forest growth ; but they also supply the strong clay soils of the broad rolling surface of till covering much of the province, sometimes rather stony, but rich in lime, potash and phosphorus derived from the ground-


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