226 DRIFT DEPOSITS AND ANCIENT EXTENSION 
the sea. Pieces of nacreous shell (belonging to a species of unio?) 
were also found in gravel, in the vicinity of Barrie, at an estimated 
height of about thirty feet above Lake Simcoe. I have found lacus- 
trine and terrestrial shells in many other places, but these I omit 
from mention, as the shells occurred on the sites of ancient swamps, 
in gullies, or in flat lands adjacent to running streams; or in other 
doubtful situations in which they may have been deposited by freshets 
and other agencies of comparatively recent date. 
Mr. Robert Bell, of the Geological Survey of Canada, has added 
greatly to the above localities, in @ valuable paper published in the 
Canadian Naturalist for February of this year (1861). Amongst 
other spots in which he has discovered fresh-water shells, the environs 
of Collingwood and Owen Sound may be cited. At the former, ex- 
amples of Planorbis trivolvis, associated with several species of helix, 
were found by him at an elevation of seventy-eight feet above Lake 
Huron. Specimens of Melania conica have been obtained, according 
to Mr. Bell, from another spot in this locality. Dr. Benjamin 
Workman, of Toronto, has also communicated the discovery of ex- 
amples of a Melania and Unio ellipsis, on the high banks of the Don, 
about thirty feet above the lake. These may have been deposited 
by the river, however, when flowing at a higher level ; but they were 
covered, according to Dr. Workman, by a considerable deposit of 
sand. 
The upper deposits of the Drift period are separable with difficulty 
in many places from those of more recent age. As the one period 
merged gradually into the other, this must necessarily be the case. 
Among the more recent deposits of Western Canada, however, our 
river “ flats’? may be more especially cited, as those of the Grand 
River, filled with the remains of land mollusca. Also, the closely- 
similar deposits of the ancient bed of the Niagara, so high above the 
present Jevel of that river; together with the shell-marls and calca-- 
reous tufas of our Jakes and streams; and our deposits of bog iron 
ore and iron ochres. 
§ 2. Deductions. 
The following deductions appear to flow naturally from the obser- 
vations recorded above : 
1. A general depression of the land, at the commencement of the 
Drift period, must have taken place to such an extent as to admit of 
