The Great Lake Basins of Canada. 143 
popularly known as the Great Lakes, but also those vast 
stretches of water which form the sources or expansions of 
the Mackenzie, Churchill and other rivers which fall into 
the Arctic Sea or Hudson Bay. Lake Superior was alluded 
to as being in part of volcanic origin, whilst the vast basin 
of Hudson Bay was referred to as being in some respects 
due to similar causes. On the other hand, Lake Athabasca, 
Great Slave Lake, Lake Winnipeg, the Georgian Bay and 
Lake Ontario lie more or less along the line where the 
limestones and sandstones meet the older Laurentian and 
Huronian strata, and he attributed their excavation to the 
action in post-tertiary times of glaciers, which, descending 
from the then greater elevations to the northward, had in 
their southern course torn away, one after another, the 
upturned edges of these softer limestones and sandstones. 
This process going on for ages, resulted in the formation of 
these lake basins. 
‘ Dr. Bell also pointed out that dykes of greenstone, Xc., 
often formed the original lines along which the channels of 
rivers, arms of lakes, and fiords were by denuding forces 
cut. 
The whole subject still merits careful investigation. Dr. 
Bell’s opinion that the Great Luke basins have a glacial 
origin, is the commonly received impression among scien- 
tists. Too much importance has, however, been attached 
to the influence of glaciers. It has been recently shown 
by Prof. J. W. Spencer that they have much less eroding 
power than has been attributed to them. If we draw rea- 
sonable conclusions, especially from correlated physical con- 
ditions as they now exist, serious difficulties present them- 
selves in the way of accepting the theory, still adhered to 
by American geologists, of a vast, continuous, continental 
glacier covering the Arctic and northern temperate regions 
of North America, and with its enormous tongues of ice 
forking into Massachusetts, New York, Indiana, Illinois, 
lowa and Wisconsin. Equally are there difficulties in the 
way of accepting the great thickness of the ice-sheet, which 
some, judging from the crushing power of a column of ice, 
