GEOLOGY OF THE TORONTO REGION 
PALAEOZOIC. 
ORDOVICIAN. 
The rocks of the Archaean are usually well 
exposed on the flanks of hills, while the valleys are 
more or less drift-covered; but the Palaeozoic rocks 
seldom rise as hills and their beds have only a slight 
dip, so that they are commonly buried under boulder 
clay or old lake deposits. Their outcrops are to be 
looked for mainly along lake shores or river valleys 
and there are hundreds of square miles of southern 
Ontario where no exposures of solid rock have been 
found. 
The Ordovician (Lower Silurian or Cambro- 
Silurian) forms the bed rock in most of the Toronto 
region, occurring at many points on the shore of 
Lake Ontario and less often at a distance from it. 
The subdivisions usually recognized are as follows: 
Queenston. 
Lorraine. 
Utica. 
Collingwood. 
Trenton. 
Black River. 
Ordovician 
Feathering out toward the north upon the uneven 
surface of the Archaean peneplain south of Bala, 
Washago and other points between Georgian Bay and 
the Thousand Islands one finds solid beds of Black 
River limestone. They are well exposed in quarries 
57 
