456 A POPULAR EXPOSITION OF THE 
In Western Canada, or rather in that portion of the Province west 
of the gneissoid belt that crosses the St. Lawrence at the Thousand 
Isles, the Post-glacial deposits consist principally of beds of sand, 
often exhibiting an oblique stratification (see fig. 54 in Parr III.) 
No marine remains of any kind have been detected in these beds. 
The shells of fresh-water mollusca, on the other hand, occur in them 
at many localities. These belong to species which still inhabit our 
lakes and streams, and comprise, more especially, the following genera : 
Unio, Cyclas, Amnicola, Valvata, Melania, Planorbis, Limnea, and 
Physa. Several species of Helix accompany these at some localities. 
Examples of fresh-water deposits of this kind, formed by causes no 
longer in action where such deposits now occur, have been recognized 
in the vicinities of Collingwood and Owen Sound; Angus station on 
the Northern Railway; Barrie, Orillia, Paris, Brantford, Toronto, 
Belleville, and other places, at various elevations from 30 or 40 to 
over 500 feet above Lake Ontario—the present surface of the latter 
being 232 feet above the sea. Fresh-water shells occur also in Post- 
glacial deposits around Niagara Falls, where, as pointed out by Sir 
Charles Lyell, many years ago, they evidently indicate the former bed 
of the Niagara River. It is only, however, within the last two or 
three years, that the occurrence of these shells throughout the lake 
area generally, has been definitely ascertained, and the true character 
of the beds in which they occur correctly shewn.* As the shells in 
question occur all over this region, and at various heights above the 
existing levels of the lakes—and as they could not have been drifted 
into their present positions by freshets, or left there, viewed collec- 
tively, by the drying up of ponds, lowering of streams, or other 
causes—they appear to indicate incontestibly the former union of our 
great lake-waters, and the consequent extension of these into a vast, 
inland, fresh-water sea. The barrier that kept up these waters on the east 
—perhaps a glacier or ice-stream, see below—was undoubtedly situated 
* The first publication on this subject was by Robert Bell, of the Geological Survey of 
Canada, in the Canadian Naturalist for February, 1861. This was followed by a more ex< 
tended article by the author of this work (who had previously communicated some of his 
observations to Mr. Bell), read before the Canadian Institute in March, 1861, and published 
in the Canadian Journal, vol. vi.. p. 221, and in the Philosophical Magazine for July of that 
year. In this paper, the former union of our lake waters, and the lacustrine origin of the 
terraces north of Toronto, &¢., was first s:nintained. A succeeding paper by the author 
(Canadian Jowrnal, November, 1861, vol. vi., p. 497), described a remarkable locality—first 
made known to him by one of his students, Mr. A. EB. Williamson, of Toronto—in which 
unios and other fresh-water types occur in great abundance, near the Nottawasaga River, 
between Lake Simcoe and Georgian Bay. ; 
