\Gla"cial\, a. [L. glacialis, from glacies ice: cf. F.
glacial.]
1. Pertaining to ice or to its action; consisting of ice;
   frozen; icy; esp., pertaining to glaciers; as, glacial
   phenomena. --Lyell.
2. (Chem.) Resembling ice; having the appearance and
   consistency of ice; -- said of certain solid compounds;
   as, glacial phosphoric or acetic acids.
{Glacial acid} (Chem.), an acid of such strength or purity as
   to crystallize at an ordinary temperature, in an icelike
   form; as acetic or carbolic acid.
{Glacial drift} (Geol.), earth and rocks which have been
   transported by moving ice, land ice, or icebergs; bowlder
   drift.
{Glacial} {epoch or period} (Geol.), a period during which
   the climate of the modern temperate regions was polar, and
   ice covered large portions of the northern hemisphere to
   the mountain tops.
{Glacial} {theory or hypothesis}. (Geol.) See {Glacier
   theory}, under {Glacier}.