MINERALS AND GEOLOGY OF CANADA. 457 
along the gneissoid belt of the Upper St. Lawrence: the line, it will 
be remembered, which separates the eastern or marine deposits of this 
period from those of lacustrine origi. In this connexion, it is inter- 
esting to observe that in the township of Pakenham (as discovered by 
Andrew Dickson, Esq.,) and also in that of Augusta, both immediately 
adjacent to this gneissoid belt, a few fresh-water types have been 
found in conjunction with shells of Zellina Grenlandica, (fig. 246), 
a marine or brackish-water species. 'The destruction of this barrier— 
whether of ice or rock—accompanied probably, and perhaps occa- 
sioned, by a gradual and periodically-interrupted depression of the 
eastern country, eventually lowered the waters to their present levels, 
and caused the formation, by denuding action, of the various ridges 
and terraces which occur so prominently throughout the lake districts. 
Those north of Toronto, described as ridges by Sir Charles Lyell, and 
thought by him to be of marine origin, are really a succession of ter- 
races rising one above another up to a height of about 760 feet above 
the present surface of Lake Ontario, and then successively descending 
towards Lake Simcoe and Georgian Bay—their abrupt or escarped 
faces being always in the direction of the nearest lake. 
The mollusca of this region during the Post-glacial period, appear ° 
to have been throughout identical with those of our present lakes and 
rivers; and most of the mammalia were of the same genera and 
species as those which now inhabit Canada. Of this latter class, the 
more common remains comprise the jaws and other parts of the 
common beaver (Castor fiber); the horns and bones of the Wapiti 
(Elaphus Oanadensis*) ; and the teeth and skull of the black bear 
(Ursus Americanus). Two at least, however, of the mammals that roam- 
ed over the shores of the great lake region during the period in question, 
are extinct. ‘These are the Mammoth, an extinct species of Elephant, 
. (Elephas primigenius); and the 
Mastodon (M. Oluoticus?). Their 
remains, hitherto found with us, 
mostly of detached molar 
teeth (fig. 248); but examples, 
o-: or less. entire, of the skull and 
Fig. 248. tusks have also been discovered. 
a—Molar tooth of Elephas primigenius. : 2 C 
é—Molar tooth of Mastodon Ohioticus. ‘Lhe sediments in which these OCeuas 
22) TO TS) se ee ee 
* The Wapiti, although at one time common throughout Canada, is now only to be found 
in the extreme northern and north-western regions. and will probably become extinct at no 
distant day. 
Vou. VIII. 2H 
