The Collaborative International Dictionary of English v.0.48:

Geology \Ge*ol"o*gy\, n.; pl. Geologies. [Gr. ge`a, gh^, the
   earth + -logy: cf. F. g['e]ologie.]
   [1913 Webster]
   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.
          [1913 Webster]

   2. A treatise on the science.
      [1913 Webster]