THE ICE: AGE 
Africa seem to show that during at least part of the Pleisto- 
cene or Glacial Period the two regions were connected. 
It is unlikely that man during the Old Stone Age had 
learned how to build canoes or rafts, so wherever he spread, 
he probably did so by walking. 
On the other hand, during a portion of the Ice Age, 
great gulfs stretched down across what is now dry land 
from the Arctic Ocean to the Caspian and Aral seas (then 
probably united) and to Lake Baikal in eastern Siberia. 
One proof of this is that in all three of these now quite 
landlocked bodies of water occur seals, which could only 
have reached them when they were connected by sea with 
the waters of the Arctic regions. 
A final characteristic result of the Ice Age to be men- 
tioned is the “river terraces” it formed. As the climate 
grew warmer with the approach of an interglacial stage, 
the melting of the ice sheets set free vast quantities of 
water, which caused great floods and freshets. These 
carried with: them much of the débris brought down by 
the glaciers from the uplands, and spread it over the 
river bottoms as sand or gravel. With the disappearance 
of the ice, the rivers, deprived of most of their supply of 
water, of course shrank in size, and began to cut for them- 
selves channels in the great beds of sand and gravel that 
they had brought down in the preceding glacial stage. 
Thus terraces formed, and sometimes we find more than 
one, the highest in each case being the most ancient. 
In the gravel and sand of certain of these river terraces, 
we find some of the earliest remains of man’s handiwork, 
in the form of rough stone implements. These include 
the Pre-Chellean, the Chellean, and the Acheulian cul- 
ture stages, when man had not yet been forced to become 
a cave dweller, but lived in open camps or at most on 
the sunny side of overhanging blufts. 
The sequence of the warm and cold epochs which to- 
gether composed the Glacial Period has been well worked 
out in the region of the Alps by Penck and Bruckner. 
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