144 Canadian Record of Science. 
have estimated in places at several miles. Scientists have 
apparently somewhat overlooked the vast effects of erosion 
by atmospheric and other agencies in Miocene and Pliocene 
ages which immediately preceded the glacial epoch, and 
the great deposits of decomposed rock which must have 
accumulated during these ages in northern temperate 
America. Nor have they fully considered the immense 
elevation, if even by accumulated ice, necessary in our 
Laurentian area and southwestward, to admit of great gla- 
ciers finding their way in a massive stream for, as in the 
Lake Michigan glacier, four hundred and more miles from 
the Laurentian or Huronian mountains, and, generally, in 
a direction which is presently up instead of down the natu- 
ral incline of the St. Lawrence valley and Great Lake basins. 
For a glacier from the Laurentian mountains to have reached 
even the head of Lake Michigan would, at the rate of pro- 
gress of the enormous Humboldt glacier in Greenland, as 
measured by Dr. Hayes, have taken about 21,000 years; 
and whilst the climates are, for argument, assumed to have 
been similar, the Greenland slope is greater than that 
through Lake Michigan could possibly have been. 
If, again, the Great Lake basins had been each over- 
spread by a vast moving glacier, there is a strong proba- 
bility that during the onward progress and the subsequent 
slow recession of the ice, the inequalities of the lake bot- 
toms must have been worn away or largely filled up with 
the debris which continually accompanied the glaciers. 
Nevertheless, Lake Michigan has a depth varying from 
700 to 1800 feet, and, excepting Lakes Erie and St. Clair, 
the other lakes have equally varying depths. 
It has, also, not been considered that continental glaciers 
even only one mile in thickness, extending over the Arctic 
and northern temperate regions of Hurope, Asia and 
America, would represent a depth of about 500 to 600 feet 
taken uniformly everywhere from the waters of the ocean 
and transformed into ice, even supposing that a milder cli- 
mate existed at the Antartic Pole. Apart from the effects 
on the general level of the continents which the weight of 
