Glacial Period
a period or epoch distinct glacial periods are traceable in ing the Newer Pliocene, and terminated the Alps, the earlier one the more severe period or GLACIER of the two. It was during the glacial period that the Alpine plants, now found on the summit of European mountains, passed S. from the Arctic regions. During the later of the two glacial periods man existed; whether he did so during the earlier one is a matter of dispute.
See GEOLOGY.
GLACIER (glas'i-er), a river of ice.
A glacier commences primarily as a frozen mass of snow, formed above the line of perpetual congelation, and consolidated partly by pressure and partly by the freezing of water infiltered into it from its surface. In the Swiss Alps the glaciers are between 20 and 30 miles long, their greatest breadth 2 or 3 miles, and their depth more than 600 feet. Why the glacier descends has been a very disputed question. Tyndall attributed it chiefly to regelation, that is, to parts of it melting and freezing again. When, in descending a mountain-side, the glacier has to force its way through a narrow channel, the brittle ice is crushed and broken, but by virtue of "regelation" it freezes anew when it has cleared the obstruction. Tyndall imitated the whole process artificially on a small scale, and his is now the accepted explanation of glacier movement. As a glacier descends, it carries with it stones, which, on its melting, are deposited in a moraine.
It makes also a dome-shaped mass of smoother rock, called in Switzerland roches moutonnées.