le to such geologists as are willing to admit the advance and
retreat of the great glacier, but yet doubt the fact of the interglacial
mild climate.

But now to return to the question of time about two hundred and twenty
thousand years ago. Then the Northern Hemisphere, according to this
theory, was in the grasp of a Glacial Age. According to Mr. Wallace,
as long as the eccentricity remained high, there could be no great
amelioration of climate, except along the southern border of the ice
sheet, which might, for causes named, vary some distance during the
Great Year. Two hundred thousand years ago the eccentricity, then very
high, reached a turning point. It then steadily, though gradually,
diminished for fifty thousand years; at that time the eccentricity
was so small, though considerably larger than at present, that it is
doubtful if it was of any service in producing a change of climate.<31>
At that time, also, the Northern Hemisphere was passing through the
Summer season of the Great Year. We ought, therefore, to have had a mild
interglacial season. Except in high northern latitudes the ice should
have disappeared. This change we would expect to find more marked in
Europe than in America.

We need only recall how strong are the evidences on this point. Nearly
all European writers admit at least one such mild interval, and though
not wanting evidence of such a period in America, our geologists are
much less confident of its occurrence.

But from that point the eccentricity again increased. So when the long
flight of years again brought secular Winter to the Northern Hemisphere,
the glaciers would speedily appear, and as eccentricity was again high,
they would again hold the country in their grasp. Fifty thousand years
later, or one hundred thousand years ago, it passed its turning point
again; eighty thousand years ago, it became so small that it probably
ceased to effect the climate. Since then it has not been very large.
Twenty-five thousand years ago it was less than it is now, but it is
again growing smaller. According to this theory, then, the Glacial Age
commenced about two hundred and twenty thousand years ago. It continued,
with one interruption of mild climate, for one hundred and forty
thousand years, and finally passed away eighty thousand years ago.

What shall we say to these results? If true, what a wonderful antiquity
is here unfolded for the human race, and what a wonderful lapse of time
is includ