The Collaborative International Dictionary of English v.0.48:

Geognostic \Ge`og*nos"tic\, Geognostical \Ge`og*nos"tic*al\, a.
   [Cf. F. g['e]ognostique.]
   Of or pertaining to geognosy, or to a knowledge of the
   structure of the earth; geological. [R.]
   [1913 Webster]