332 On the Geology of the Northwestern Regions of America. 
Sazicava rugosa, &c.); the whole crowned by an immense pro- 
fusion of boulders and erratic blocks. The country forming the 
Hudson’s Bay Territories is too flat for the immense erratic for- 
mation extending over every part of it to be explained by refer- 
ence to the motion of glaciers; and I think it is more probably 
due to the action of icebergs and floating masses of ice, still so 
common along these coasts, and which are without ow" per- 
forming at the present day precisely a similar office, in strewing 
the bed of the ocean in which they ry found with the ‘iwc 
transported from the adjacent shores 
ith reference to the character jer the pleistocene or drift 
formation, it may be mentioned that as we ascend the rivers of 
this region, especially along the basins of Lake Winipeg and its 
affluents in the prairie districts, the sandy and clayey deposits are 
found to abound with land and freshwater shells, suchas Unio, 
Helix, Pupa, &c., of species now living on the borders, or in the 
beds of the rivers and lakes. The cliffs containing these shells 
are often raised more than 100 feet above the present levels of 
the banks of the streams, and appear to be ancient lake- or river- 
terraces ; leading to a belief that, great as is the present extent 
of freshwater surface in the North American Continent, it was at 
one time still greater, and that the existing series of lakes; from 
the St. Lawrence northward, were perhaps anciently united in 
one or more vast freshw ater seas, having their western margins 
indicated, perhaps, by the peculiar elongated strip ernie by 
the lignite-formation previously described, which presents pre- 
cisely the appearance which would result from a long on of 
shelving beach, piled with masses of drift-wood accumulated 
through long successive periods, similar to what is now found 
covering the + shores of the inland lakes and portions of the coasts 
of the Arctic Seas. 
It has been stated as an exemplification of the wide changes 
which would result from a comparatively small alteration in the 
present level, even of such mountainous districts as Canada and 
the Northeastern States of the Union, that “a subsidence of 400 
feet would cause the waters of Lake Ontario, to flow through 
the valleys of the Mohawk and Hndson into the Atlantic, and at 
the same time: convert Lake Champlain into a maritime strait, 
thereby forming islands of the States of New York, New Eng- 
land, and Maine, and of the British Colonies of New Brunswick 
and Nova Scotia.” A subsidence of one-fourth of that amount 
in the prairie districts of the Saskatchewan, continued to Great 
the Appendix to Dr. Scoresby’s ‘Journal of a Voyage to the Northern 
Whale Fishery, Professor Jameson enumerates among the 5 specimens found on an 
iceberg near pe Brewster the following :— 
1. Transition clay slate. 4, Hornblende mica-slate. 
2. Slaty talcose granite. 5. is * 2 
3. Granular felspar. 6. Basaltic greenstone. = 
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