Great Lake Basins of the St. Lawrence. 277 
underlying rocks to the immediate east, south and west of 
the lake, and the way in which they converge at the south- 
ern extremity of the Georgian Bay. A similar opinion 
may be ventured regarding the Medina sandstones. Prof. 
Bell, referring to Lake Ontario and certain other lakes, 
thinks that the glaciers descending from the higher grounds 
against the upturned edges of the softer rocks, tore them up 
rapidly, and carried away the debris, thus leaving the lake 
basins. The sharply defined edges of the escarpment, its 
generally bold face, and the comparatively short distance 
it has apparently receded, would, however, rather indicate 
in its case atmospheric effects, the wearing force of rivers, 
and the undermining action of waves upon an open lake or 
sea coast. 
Sir William Logan, in the Geology of Canada, points out 
the resemblance of the Niagara escarpment, in places, to 
an ancient sea cliff. He also shows that it merely requires 
a depression of 442 feet to bring the ocean into Lake Ontario 
by way of the Hudson River and the Mohawk Valley, as 
well as by the St. Lawrence, and to inundate the whole of 
Central Ontario, although he did not then think that there 
was evidence that such an inroad had taken place. Such a 
depression would lead to the ocean penetrating as far west 
as the Niagara escarpment, and as far northward, in some 
places, as the Laurentian hills. The Georgian Bay would 
still be 140 feet above the ocean level, but if the thick de- 
posits of sands, gravels and clays, between it and Lake 
Ontario, the positions of some of which are attributable to 
relatively very recent times, had not then existed, or were 
cut through at any point, the Georgian Bay would have 
been lowered to the ocean level, and have formed part of 
the same interior ocean as Lake Ontario, This would bring 
to the surface the presently submerged ridge between the 
jruce peninsula and the Manitoulin Islands, owing to the 
lowering of Lakes Huron and Michigan to the level of the 
surface of the ridge. The outlet of these lakes would there- 
after be over this ridge, and not by way of Lakes St. Clair 
and Erie. Now, the deep water cliffs on the eastern side of 
