Source : Webster's Revised Unabridged Dictionary (1913)

Geology \Ge*ol"o*gy\, n.; pl. {Geologies}. [Gr. ge`a, gh^, the
   earth + -logy: cf. F. g['e]ologie.]
   1. The science which treats:
      (a) Of the structure and mineral constitution of the
          globe; structural geology.
      (b) Of its history as regards rocks, minerals, rivers,
          valleys, mountains, climates, life, etc.; historical
          geology.
      (c) Of the causes and methods by which its structure,
          features, changes, and conditions have been produced;
          dynamical geology. See Chart of {The Geological
          Series}.

   2. A treatise on the science.