\Nep*tu"ni*an\, a. [L. Neptunius belonging to Neptune:
cf. F. neptunien.]
1. Of or pertaining to the ocean or sea.
2. (Geol.) Formed by water or aqueous solution; as, Neptunian
   rocks.
{Neptunian races} (Ethnol.), the Malay and Polynesian races.
{Neptunian theory} (Geol.), the theory of Werner, which
   referred the formation of all rocks and strata to the
   agency of water; -- opposed to the Plutonic theory.

\Nep*tu"ni*an\, Neptunist \Nep"tu*nist\, n. [Cf. F.
neptinien, neptuniste.] (Geol.)
One who adopts the neptunian theory.