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Page:Popular Science Monthly Volume 4.djvu/673

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THE AGE OF ICE.

tem of planets through a much warmer region than the space now encircling us.

Centres of Dispersion.—All existing glaciers flow from higher to lower levels as a rule—the only exception being that already stated, when the ice may be forced up-hill for a short distance. This may be well exemplified in the Alpine glaciers of the present day. These streams of ice all flow from the summits and axes of particular mountains along the valleys, and spread over the neighboring plains. The action is radial—proceeding from a central point or line outward.

Fig. 10.
PSM V04 D673 Alpine glacier.jpg
Alpine Glacier. (H. M. Skae.)

The geologists have concluded that most of the ancient ice-movements in Northern Europe have been from centres of dispersion, like those in Switzerland. Examples are numerous. One of the most interesting is exhibited in Switzerland. The traveler finds there two prominent centres of glacial radiation—the Bernese and the Mont Blanc regions. Glaciers now flow westerly into the great valley of Switzerland and toward the Rhone from the former, and in the latter group the streams discharge upon the Italian plains on the south, and toward the vale of Chamouni on the north. A careful study of the vale of Chamouni shows that ice once filled it to the brim, for the embossed rocks carry striæ even to the height of 5,000 feet.