ef Summer, and the mild interglacial age will have passed away,
and again the Northern Hemisphere will be visited by snow and ice of a
truly. Glacial Age. If, therefore, a period of high eccentricity lasts
through the many thousand years, we must expect more than one return of
glacial cold interspersed by mild interglacial climates.

We have tried in these last few pages to give a clear statement of what
is known as Croll's theory of the Glacial Age. There is no question but
what the earth does thus vary in its position with regard to the sun,
and beyond a doubt this must produce some effect on the climate, and
we can truthfully state that the more the complicated question of the
climate of the earth is studied, the more grounds do scholars find for
affirming that indirectly this effect must have been very great. And yet
we can not say that this theory is accepted as a satisfactory one even
by the majority of scholars. Many of those who do not reject it think
it not proven. Therefore, before interrogating the astronomer as to the
data of the Glacial Age, according to the terms of this theory, let us
see what other causes are, adduced; then we can more readily accept
or reject the conclusions as to the antiquity of man which this theory
would necessitate us to adopt.

The only other cause to which we can assign the glacial cold, that is
considered with any favor by geologists, is geographical; that is to
say, depending on the distribution of land and water. Glaciers depend on
the amount of snow-fall. In any country where the amount of snow-fall
is so great that it is not all evaporated or melted by the Summer's sun,
and consequently increases from year to year, glaciers must soon appear,
and these icy rivers would ere-long, flow away to lower levels. If we
suppose, with Sir Charles Lyell, that the lands of the globe were all to
be gathered around the equator, and the waters were gathered around the
poles, it is manifest that there would be no such a thing as extremes of
temperature, and it is, perhaps, doubtful whether ice would form, even
in polar areas.<18> At any rate, no glaciers could be formed, as there
would be no land on which snow could gather in great quantities.

If, however, we reverse this picture, and conceive of the land gathered
in a compact mass around the poles, shutting out the water, but consider
the equatorial region of the earth to be occupied by the waters of the
ocean, we would manifestly have a