248 Canadian Record of Science. 
and geological features of the surrounding country, the 
fauna of their depths, and the flora of their shores, furnish 
us with facts for the compilation of their history ? 
The object of the present paper is to suggest what has 
been the origin of the contours of the Great Lakes as they 
now present themselves. All writers on the subject are 
probably agreed that at a relatively recent quaternary 
period these lakes have been united consequent on a depres- 
sion of the land, greatest at Lake Superior, and lessening 
towards the present St. Lawrence outlet. That in the pre- 
vious glacial period this greater lake was a still larger inland 
sea extending farther southward, into which glaciers from 
the then more elevated Laurentian area, and rivers having 
their sources at the glaciers, flowed, and across whose sur- 
faces floated icebergs and icefloes, carrying their burdens 
of boulders and debris in the direction in which the currents 
impelled them, has always appeared the most reasonable 
view to take. The depression would be a natural result of 
a rise of land to the north. It has not hitherto been suf- 
ficiently considered that whatever changes in level take 
place, the maintaining of an equilibrium in the earth’s 
crust can in general terms be predicated. If there is a 
great subsidence in the land over any extended area, it may 
be assumed that there is a corresponding rise in the land 
over some other area. Thus, if over the Laurentian region 
there was an increase in height which gave some slope and 
consequently denuding power to the glaciers which flowed 
to the north and northeastward on the one side of the Lau- 
rentian axis, as shown by Drs. G. M. Dawson and Bell, and 
to the southwestward on the other, then we can accept the 
assumption that immediately to the southward or north- 
ward, or both, there might reasonably be an extensive de- 
pression of the land and an inflow of the sea. This inflow 
on the southward side also found its way, no doubt contem- 
poraneously, as far west as the Rocky Mountains, as the 
enormous boulders and other features discovered by Dr. 
G. M. Dawson indicate. And there seems to be corrobora- 
tive evidence of this inflow in the flora around the lakes 
