The Collaborative International Dictionary of English v.0.48:

Hypogene \Hyp"o*gene\, a. [Pref. hypo- + the root of Gr. ? to be
   born: cf. F. hypog[`e]ne.] (Geol.)
   Formed or crystallized at depths beneath the earth's surface;
   -- said of granite, gneiss, and other rocks, whose
   crystallization is believed of have taken place beneath a
   great thickness of overlying rocks. Opposed to epigene.
   [1913 Webster]