Identifier: environmentofcam39sali (find matches)
Title: The environment of Camp Grant
Year: 1918 (1910s)
Authors: Salisbury, Rollin D., 1858-1922 Barrows, Harlan H. (Harlan Harland), b. 1877
Subjects: Geology
Publisher: Urbana, Ill.
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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by long accumulation the ice formed from snow becomes verythick, it begins to spread. The ice-cover of Greenland is creeping slowlyout from the central part of the island where the ice is thickest, towardthe borders where it is thin. Similarly, the ice-sheet which formerly cov-ered some millions of square miles *in the northeastern part of North 40 THE ENVIRONMENT OF CAMP GRANT America (fig. 20), moved slowly out from certain centers where it wasthickest, toward its edges where it was thin. This period of the earthshistory, known as the Glacial Period, was relatively recent compared withthe time when the limestone of the region was being deposited on the seabottom; but in terms of human history it was long ago. One of the strange things about the glacial period is the fact thatthere were several great ice-sheets, one after another, separated by periodswhen the climate was relatively mild. During at least one of these inter-glacial epochs, we know that the climate was warmer than now.
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Fig. 20.—Map showing the extent of glaciation in North America,al Paper 106, U. S. Geological Survey. Profession- HISTORY OF THE LAND 41 All the ice-sheets were not equally extensive, and no two of themcovered exactly the same area. The region about Camp Grant was over-spread by at least two of them, and perhaps by more. That more than

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