about the same rate as that of the moving ice.
Undoubtedly the average movement was very slow and was probably
thousands of years reaching its southernmost limit, which is now marked
by the terminal moraine. Thus it will be seen that while the individual
trees and plants could not move, the forest as a whole could. It was
gradually being cut down on its northern limit and as gradually it grew
up on the southern limit of the zone; the ice movement being so slow
that the young tree of to-day on the southern limit becomes a full-grown
king of the forest by the time the relentless icebergs reach it and cut
it down and thus the process went on until the plants, trees, and
animals of the arctic region were driven hundreds of miles south of the
great chain of lakes on the northern boundary of the United States.

Many of the animals of preglacial times were unable to stand the strain
of the ever-changing climatic conditions and have become extinct, but
their fossil remains are left to tell the story to the present and
future ages. Much of the history of those times is a sealed book, but
the persevering energy of the glacialist and archaeologist is gradually
turning the leaves of this old book and revealing new chapters of the
wonderful story of the ice.

As the ice receded the arctic zone again traveled northward, and many
animals, plants, and trees that had survived the vicissitudes of the ice
age, traveled back with it. Some of them, however, became acclimated and
by adapting themselves to the new conditions remained behind to live and
grow with the aborigines of preglacial times. Some of the plants and
flowers that grew in profusion immediately under the edge of the great
ice sheet were unable to live under the new conditions of increased
warmth--that came with the retrograde movement of the ice--and either
had to follow closely the receding ice or escape to higher altitudes,
where they found a congenial clime. Thus it is that we have arctic
plants and flowers above the timber line and near the snow line of our
high mountains. In proof of this theory it has been found that these
arctic plants do not exist upon high mountains, such as the Peak of
Teneriffe, where they have been isolated from the glaciated region. The
Peak of Teneriffe is situated on one of the Canary Islands, surrounded
by water, so that there was no possible chance for the arctic plants to
seek refuge on these isolated elevations, such as the continental
mo