NATURAL HISTORY, TORONTO REGION 
mation, the Ordovician, follows after an interval 
long enough to destroy the Laurentian mountains, 
which were carved down to low hills, the region 
having been reduced to a peneplain. 
Though the Archaean rocks are not found in place 
within ninety miles of Toronto, specimens of all 
their varieties, including marble, may be collected 
from the drift boulders in the neighborhood of the 
city. 
The old Archaean surface sinks gently beneath 
the next sheet of rock and advancing southwards 
may be found by drilling at greater and greater 
depths below the surface. At Thornhill, fourteen 
miles north of Toronto, it has been found in a well 
at 1,200 feet below the surface and 600 feet below 
the level of Lake Ontario. At Toronto granite and 
gneiss and sometimes crystalline limestone are found 
at depths of 1,100 to 1,300 feet below Lake Ontario, 
showing a slope of about forty feet to the mile in the 
old land surface. It is nearly 1,000 feet below sea 
level at Toronto, and 2,500 on the north shore of 
Lake Erie. 
As the ancient surface must have been leveled to 
a peneplain by denuding forces which can only act 
above the level of the sea, it is evident that vast areas 
of the old continental mass were warped down to 
form sea bottom before the Palaeozoic history of the 
region began. 
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