A knowledge of the mechanical behavior of geologic materials (rocks and minerals) has become increasingly important in mining and civil engineering, geology, geophysics and more recently in a number of defense and aerospace fields. This research describes an investigation of one particular aspect of the mechanical behavior of these materials namely the determination of their inelastic properties. The investigation consisted of two stages; first, the development of suitable test facilities and experimental techniques, and second, the detailed study of the deformation properties of a relatively simple geologic materials namely, Wombeyan marble. / Ph. D.