Great Lake Basins of the St. Lawrence. 249 
and in the fauna of their depths, as will be shown hereafter. 
That in the St. Lawrence Basin this inland sea graduated 
by a general elevation of the land and by local warpings of 
the strata into the more circumscribed fresh-water lake 
before referred to as including the area of the present lakes, 
there seems no question. That, however, prior to this an 
interglacial period prevailed, to be followed by a second 
glacial period, there is not in Eastern Canada very satisfac- 
tory evidence, whatever credence we may give to the 
vegetal deposits relied on by some American geologists 
to prove more than one interglacial period, and to the peaty 
remains in the Canadian superficial deposits towards the 
Rocky Mountains. 
The grave difficulties which on general physical grounds 
stand in the way of the larger conception of a continental 
ice-sheet, need not be repeated here. It may be well, how- 
ever, to allude to one circumstance—the immense mass of 
the superficial deposits—which hasbeen relied on as neces- 
sitating a glacial theory for its explanation, and which has 
a direct association with the history of the St. Lawrence 
Basin. It has been usual to ascribe largely to glacial action 
what must be the effects of ages of subereal and sub-aqueous 
erosion and decay in this great lake basin since the Carbo- 
niferous age. Whilst most sections were above water for 
vast periods prior to the Carboniferous, the whole of the im- 
mense area drained by the Great Lakes has, subsequent to 
that period, and as far onwards as quaternary times, been 
dry land, excepting to the extent that these lakes, or any of 
them, may have themselves been in existence during the 
immense intermediate periods—periods measured not by 
centuries alone, but probably by countless centuries of cen- 
turies. All of the agencies ordinarily at work in producing 
growth, disintegration and decay were then in operation, 
and have been continuously since. Forests covered the 
land, and vegetation in its decay everywhere yearly con- 
tributed to the soil; torrents found their way to the rivers, 
and the rivers to the lakes and to the ocean, creating on 
their way boulders and gravel, and depositing clays and 
