NATURAL HISTORY, TORONTO REGION 
Spirifera duodenarius. 
Stropheodonta demissa. 
Conocardium cuneus. 
Paracyelas elliptica. 
Platyceras carinatum. 
Proetus rowi. 
PLEISTOCENE. ‘ 
GENERAL FEATURES. 
As previously mentioned, the greater part of the 
region under consideration is covered with drift 
deposits of the Pleistocene, sometimes to the thick- 
ness of 600 or 700 feet; and a very complex history 
has been worked out from them. Between the 
Devonian and the end of the Pliocene no record has 
been preserved, but it is certain that superficial ero- 
sion went on to a great extent in the long period of 
dry land conditions after the middle Palaeozoic. 
There was time to strip much of the Palaeozoic beds 
from the Archaean floor and to cut back for many 
miles toward the west and south the Silurian shales 
under their protective capping of Niagara limestone, 
thus producing the striking escarpment which crosses 
the province. Great river valleys were carved below 
the present level of the sea, showing that the land 
stood higher than now, the most important being 
the “ Laurentian River,” as it has been named by 
Dr. Spencer, which drained the Upper Lakes region 
through what is now Georgian Bay to the Ontario 
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