\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.
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.
{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.