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From The Collaborative International Dictionary of English v.0.48:
Glacier \Gla"cier\, n. [F. glacier, fr. glace ice, L. glacies.] An immense field or stream of ice, formed in the region of perpetual snow, and moving slowly down a mountain slope or valley, as in the Alps, or over an extended area, as in Greenland. [1913 Webster] Note: The mass of compacted snow forming the upper part of a glacier is called the firn, or n['e]v['e]; the glacier proper consist of solid ice, deeply crevassed where broken up by irregularities in the slope or direction of its path. A glacier usually carries with it accumulations of stones and dirt called moraines, which are designated, according to their position, as lateral, medial, or terminal (see Moraine). The common rate of flow of the Alpine glaciers is from ten to twenty inches per day in summer, and about half that in winter. [1913 Webster] Glacier theory (Geol.), the theory that large parts of the frigid and temperate zones were covered with ice during the glacial, or ice, period, and that, by the agency of this ice, the loose materials on the earth's surface, called drift or diluvium, were transported and accumulated. [1913 Webster]