terminal moraines, all point to a much shorter period since the ice
age than it used to be supposed, and indicate that the time does not
exceed 10,000 years.

To the ordinary mind the ice age no doubt seems like a myth, but to the
man of science who has made a study of all of these evidences it is as
real as any fact in history, and much more real than some of the history
we read. In the former case we are dealing with evidences that appeal to
our senses, while in the latter we are dealing with the recollections of
men concerning what purport to have been actual transactions, and we
know enough about the human mind to make it difficult sometimes to draw
the line between the actual and the imaginary.

The glacial period is not only closely related to the topography of
North America and parts of Europe in the changing of river beds, the
formation of lakes, the transportation of rock, the grinding down of
mountains and spreading the debris over thousands of miles in extent,
but it is related in an intimate way to many of the sciences, such as
botany and zooelogy. A study of the flight of animals and plants in front
of the great advancing ice sheet is a subject of intense interest. The
migration of great forests would seem to be an impossible thing when
viewed from the standpoint of a casual observer. It is true that
individual trees could not take themselves up and move forward in
advance of the oncoming ice, but they could and did send their children
on ahead, and when the ice had overtaken the children there were still
the children's children ad infinitum.

By an examination of the map it will be seen that the land gathers about
the north pole, while the south pole is surrounded chiefly by great
oceans. As we have hinted before, in preglacial times the temperate zone
extended much farther north than it does to-day, and north of that there
was an arctic zone (which to-day is largely covered with ice sheets),
where forests, plants, and animals flourished that were fitted for an
arctic climate. When the glacial period set in and the ice sheet began
its southern journey this zone or climate was moved southward in front
of the ice, thus forming, as it were, a moving zone whose climatic
conditions were similar to those of the arctic regions (at least so far
as temperature was concerned) in preglacial times. The ice movement was
so gradual that time was given for forests to spring up in advance of it
that moved southward at