"dirt-eating," 1820, from Greek *geophagia (according to OED the actual Greek is geotragia), from geo-, comb. form of ge "earth" (see Gaia) + phagein "to eat." See also pica (n.2).
A diseased appetite ... prevails in several parts of Alabama, where they eat clay. I heard various speculations on the origin of this singular propensity, called 'geophagy' in some medical books. [Lyell, "Second Visit to U.S.," 1850]