The Gault Clay is a formation of stiff blue clay deposited in a calm, fairly deep water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). It is well exposed in the costal cliffs at Copt Point in Folkestone, Kent, England, where it overlays the Lower Greensand Formation.

The Gault Clay often contains numerous phosphatic nodules and may also contain sand as well as small grains of the mineral glauconite. Crystals of the mineral selenite are fairly common in places, as are nodules of pyrite.

The Gault Clay yields abundant marine fossils, including ammonites (such as Hoplites, Hamites, Euhoplites, Anahoplites, and Dimorphoplites), belemnites (such as Neohibolites), bivalves (such as Birostrina and Pectinucula), gastropods (such as Anchura), solitary corals, fish remains (including shark teeth), scattered crinoid remains, and crustaceans (such as the crab Notopocorystes). Occasional fragments of fossil wood may also be found.

The Gault Formation consists of both the Gault Clay and Upper Greensand.

The Gault exposure at Copt Point, which is the type locality for the formation, is 40 m in thickness.

See also

• Geology of the United Kingdom