stone boulder used for
throwing and hammering, the developed product made by chipping and
polishing the natural boulder, making it more useful and more
beautiful, and so for all the {62} multitude of implements used in the
hunt and in domestic affairs. Not only do we have here an illustration
of continuous progress in invention and use, but also an adaptation of
new material, for we pass from the use of stone to that of metals,
probably in the prehistoric period, although the beginnings of the use
of bronze and iron come mainly within the periods of historical records.

It is not possible here to follow the interesting history of the
glacial movement, but a few words of explanation seem necessary. The
Ice Age, or the glacial period, refers to a span of time ranging from
500,000 years ago, at the beginning of the first glaciation, to the
close of the post-glacial period, about 25,000 years ago. During this
period great ice caps, ranging in the valleys and spreading out on the
plains over a broad area, proceeded from the north of Europe to the
south, covering at the extreme stages nearly the entire surface of the
continent. This great movement consists of four distinct forward
movements and their return movements. There is evidence to show that
before the south movement of the first great ice cap, a temperate
climate extended very far toward the pole and gave opportunity for
vegetation now extinct in that region.

But as the river of ice proceeded south, plants and animals retreated
before it, some of them changing their nature to endure the excessive
cold. Then came a climatic change which melted the ice and gradually
drove the margin of the glacier farther north. Immediately under the
influence of the warm winds the vegetation and animals followed slowly
at a distance the movement of the glacier. Then followed a long
inter-glacial period before the southerly movement of the returning ice
cap. This in turn retreated to the north, and thus four separate times
this great movement, one of the greatest geological phenomena of the
earth, occurred, leaving an opportunity to study four different glacial
periods with three warmer interglacial and one warm post-glacial.

This movement gave great opportunity for the study of {63} geology,
paleontology, and the archeology of man. That is, the story of the
relationship of the earth to plant, animal, and man was revealed. The
regularity of these movements and the amount