The fourth method is to study the procession of man by (4) cultures, or the industrial and ornamental implements that have been preserved in the river drift, rocks, and caves of the earth from the time that man used them until they were discovered. Just as we have to-day models of the improvement of the sewing-machine, the reaper, or the flying-machine, each one a little more perfect, so we shall find in the relics of prehistoric times this same gradual development—first a stone in its natural state used for cutting, then chipped to make it more perfect, and finally beautified in form and perfected by polishing.

Thus we shall find progress from the natural 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 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 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 of material evidence found furnish a great opportunity for measuring geological time movements and hence the life of plants and animals, including man.

The table on page 64 will contribute to the clearness of this brief statement about the glacial periods.

THE ICE AGE IN EUROPE[[5]]
Geological time-unit 25,000 years
RELA-
TIVE TOTAL
TIME TIME HUMAN ANIMAL AND
GLACIERS UNIT YRS. YRS. LIFE PLANT LIFE
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Post-Glacial 1 25,000 25,000 Crô-Magnon Horse, Stag, Rein-
Daum Azilian deer, Musk-Ox,
Geschintz Magdalenian Arctic Fox, Pine,
Bühl Solutrian Birch, Oak
Aurignacian
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4th Glacial 1 25,000 50,000 Mousterian Reindeer, period of
Wurm Ice Neanderthal Tundra, Alpine,
Steppe, Meadow
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Q 3d Inter- 4 100,000 150,000 Pre-Neander- Last warm Asiatic
U glacial thal and African ani-
A Piltdown mals
R ---------------------------------------------------------------------------
T 3d Glacial 1 25,000 175,000 Woolly Mammoth,
E Riss Rhinoceros,
R Reindeer
N ---------------------------------------------------------------------------
A 2d Inter- 8 200,000 375,000 Heidelberg African and Asiatic
R glacial Race Animals, Ele-
Y Mindel-Riss phant, Hippo-
potamus
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2d Glacial 1 25,000 400,000 Cold weather
Mindel animals
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1st Inter- 3 75,000 475,000 Pithecan- Hippopotamus,
glacial thropus Elephant, Afri-
Erectus can and Asiatic
plants
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1st Glacial 1 25,000 500,000
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