File:Carnegie Institution of Washington publication (1914) (20348101970).jpg

Title: Carnegie Institution of Washington publication
Identifier: carnegieinstitut192carn (find matches)
Year: 1914 (1910s)
Authors: Carnegie Institution of Washington
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Publisher: Washington, Carnegie Institution of Washington
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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266 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. of the melting glaciers the land was strewn with erratics, with thick accumulations of heterogeneous rocks deposited at the edge of ice-sheets and known as moraines, and with great fans of boulder-clays and sands, all of this being the diluvium or deluge material of the older philosophers and the drift or tills of modern students of earth science. Throughout more than a century of study we have learned how glaciers do their work and what results are accomplished by their motion plus the action of temperature, air, and water. The present geographic distribution of the glaciers, together with that of the glacial deposits, shows us that during the Pleistocene or glacial period the temperature of the entire earth was lowered. We also know that this cold period was not a uniformly continuous one, but that during the Pleistocene there were no less than four intermediate warmer cUmates, so warm indeed that during one of them Uons and hippopotamuses lived in western Europe along with primitive man. We may now be living in another inter- glacial warm period, though more probably we are just emerging from the Pleistocene ice age. Figure 87 gives the known distribution of Pleistocene glacial materials.
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Fig. 87.—Map of Pleistocene Glaciation. With the reduction of temperature, great variations also took place in the local supply of moisture, in the number of dark days, and in the air currents. How great these changes were in Pleistocene time is now being revealed to us through the work of the geologists, paleontologists, and ethnologists of Europe, where this record is far more detailed than in North America. These observations picture a fierce struggle on the part of the hardier organisms against the colder climates, a blotting out of those addicted to confirmed habits and to warmer conditions, and a driving southward of certain elements of the flora and fauna from the glaciated into the non-glaciated regions. The result was the disestablish-

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