Pertaining to autochthons; indigenous; sprung from the soil; aboriginal.In pathology, not extraneous; originating at the place where found.In petrol., noting rocks which have originated in situ, such as peat, rock-salt, and stalagmitic limestone; also applied to constituent minerals of rocks which have crystallized in the place they now occupy. Autochthonous materials are contrasted with the mechanically derived particles of clastic rocks.