\Lith"o*sphere\, n. [Litho- + sphere.] (Phys. Geog.)
(a) The solid earth as distinguished from its fluid
    envelopes, the hydrosphere and atmosphere.
(b) The outer part of the solid earth, the portion undergoing
    change through the gradual transfer of material by
    volcanic eruption, the circulation of underground water,
    and the process of erosion and deposition. It is,
    therefore, regarded as a third mobile envelope comparable
    with the hydrosphere and atmosphere.