Hyp"o*gene (?), a. [Pref. hypo- + the root of Gr. &?; to be born: cf. F. hypogène.] (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.