Geological Contact

the contact surface of rocks that form contiguous sections of the earth’s crust. Geological contacts are classified as normal, or stratigraphic, when sedimentary or effusive rock is deposited on older rock; intrusive, if comparatively young intrusive rock has broken through older rock, causing various changes in it; and tectonic, when rocks of different content, origin, and age adjoin along the surface of a tectonic fault.