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. 



