could dig out and root out a hole, as in the case of Lake Superior,
_nine hundred feet deep!_

{p. 96}

And, if it did this, why were not similar holes excavated wherever
there were ice-sheets--to wit, all over the northern and southern
portions of the globe? Why should a general cause produce only local
results?

Sir Charles Lyell shows[1] that glaciers do not cut out holes like
the depressions in which the Great Lakes lie; he also shows that
these lakes are not due to a sinking down of the crust of the earth,
because the strata are continuous and unbroken beneath them. He also
calls attention to the fact that there is a continuous belt of such
lakes, reaching from the northwestern part of the United States,
through the Hudson Bay Territory, Canada, and Maine, to Finland, and
that this belt does not reach below 50° north latitude in Europe and
40° in America. Do these lie in the track of the great collision? The
comet, as the striæ indicate, came from the north.

The mass of Donati's comet was estimated by MM. Faye and Roche at
about the seven-hundredth part of the bulk of the earth. M. Faye says:

"That is the weight of a sea of forty thousand square miles one
hundred and nine yards deep; and it must be owned that a like mass,
animated with considerable velocity, might well produce, by its shock
with the earth, very perceptible results."[2]

We have but to suppose, (a not unreasonable supposition,) that the