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angles to each other, as in the monoclinic system, but both 
inclined to the vertical axis. 
THE PRESIDENT gave the second paper announced for the 
evening, “ On the Structure and Origin of the Great Lakes,” 
of which the following is a brief abstract. 
The surface-contour of a country at any given time is the 
result of the counter-action of two ever-contending forces, 
elevation and erosion. After sketching the character of the 
Laurentian Highlands of Canada, which represent the oldest 
land on our continent, as everywhere planed down and worn 
away, from their ancient height, into low, smooth, rolling 
hills, he traced the formation of the great ‘plain-country 
which borders them all around. The wear of untold ages, 
and the repeated invasions of the Paleozoic seas [see page 
123], have formed from these primeval mountains the broad 
area of sedimentary rocks, Silurian, Devonian, and Carboni- 
ferous, which spreads away southward and westward from 
their base, for the most part unaltered and undisturbed. 
These Laurentian hills must have been anciently snow- 
capped and ice-clad. Of course this was the case in the 
glaciai epoch; but it may, perhaps often, have occurred be- 
fore. If we study the action of glaciers now, we find that 
the head of the ice-mass, on reaching the lowland, or the sea- 
bottom, if it strikes the coast—tends to plow out a valley or 
depression in the soft material of the soil or the sea-bed. If 
the glacial action is long-continued or oft-repeated, such 
valleys may become very deep ; this we know is the case on 
the Greenland coast, even where the force of the glaciers is 
lessened and limited by the buoying-up and breaking off of 
their outer ends by the sea. 
In the light of such considerations, we may now observe 
the characters of our Western Lakes. 
The whole chain of the Great North American Lakes may 
be seen to occupy a series of basins excavated in the plateau 
which skirts the base of the Canadian Highlands. Save in 
the case of Lake Superior, the outlines of which are partially 
determined by upheaval, all the lake basins are excavated in 
nearly horizontal sedimentary rocks. Their sides and bot- 
toms, so far as can be examined, are planed and grooved in 
a manner which is produced only by glacial action; and the 
proof is conclusive that each of these basins has been filled, 
and at least partly excavated, by a mass of moving ice. The 
direction of the furrows on the rock, and the trail, left behind 
