Gault

Gault (a local name in Cambridgeshire for clay) is one of the subdivisions of the Cretaceous System (q.v.). The gault is a stiff, bluish-gray clay, which here and there contains indurated nodules and septaria. Now and again it becomes somewhat calcareous, or sandy and micaceous. In some parts of Sussex a band of phosphatic nodules occurs at its base. The deposit is of variable thickness—reaching in some places over 300 feet, while occasionally it hardly attains a greater thickness than 50 feet, and forms a well-marked geological horizon—forming the bottom member of the Upper Cretaceous rocks. It is abundantly fossiliferous, the remains being almost exclusively marine, only a few drifted land-plants having been met with. One of the best exposures of the gault in England is at Folkestone. In the Isle of Wight this formation is known as the 'blue slipper,' from the readiness of the overlying beds to slip or slide over its surface. The picturesque 'Undercliff' owes its origin to these landslides. The gault is extensively employed in the manufacture of bricks and tiles; it forms a retentive and rather unproductive soil.