Gault

Gault, a provincial name for a blue clay applied in English geology to the Albian or lower division of the Upper Cretaceous rocks. As developed in England, it is generally a stiff blue marine clay, sometimes slightly calcareous, sandy, or micaceous, containing abundant nodules of iron-pyrites, generally a layer of phosphatic nodules near its base, and a large number and variety of pyritised or phosphatised fossils. It often overlaps the subjacent rocks unconformably and varies from 100 to 150 or even 200 feet in thickness. In the Isle of Wight it is termed "blue slipper," from the tendency of overlying porous strata to slide over it, producing landslips (q.v.). The Gault may be examined about Barnwell in Cambridgeshire, at various points in the Weald, and especially near Folkestone, where it has been subdivided into eleven paleeontological zones (q.v.), of which seven belong to the Lower Gault or Hamites rotundus section, and four to the Upper Gault or Inoceramus sulcatus section. Of 240 fossils, 124 are peculiar tc the Lower, 59 to the Upper, and only 39 common to both. Gastropods and bivalves abound in the Lower, with such cephalopods as Hamites, "n ceres, Anci/loceras, etc., and several species of small crabs; whilst Scapliites occurs in the Upper, and numerous ammonites throughout both divisions, often retaining their nacreous or pearly lustre. Dentalium and Belemnites are also common, and fir-cones indicate the proximity of land. The Gault forms a stiff soil mostly in pasture and known as "black land." It bears fine trees, especially oaks, and it is dug for brick-making.