6 GAULT. 



XV. The Tipper Clays and Sand Rock consist of forty feet of dark clay with pyrites, 

 separated by eighteen feet of white and green-coloured sand from a mass of clays and 

 sands sixty feet thick. The bed 47 of this group is dug near Rocken End for the 

 manufacture of glass ; it contains no fossils. 



XVI. Various Sands and Clay constitute the remainder of the section ; they measure 

 about 120 feet in thickness, and are overlain by the Gault. 



The Lower Greensand represents the upper portion of the rocks known as the 

 Terrain Neoconiien of MM. Thurmann and d'Orbigny ; Terrain Jurassique superieur of M. 

 Matheron ; Couches adosse'es au Jura of Von Buch ; Formation Waldienne et Neocomienne 

 of I\IM. Dufrenoy and Elie de Beaumont ; Calcaire a Sjmtaiiyues, L'Argile ostreene, of 

 M. Cornuel ; Arr/iles tegulines et gres vert and " Terrain Neocomien " (Wealden) of M. 

 Leymerie. The French geologists consider the Wealden clay and Hastings sand as the 

 inferior, and the Lower Greensand the superioi-, portion of their Neocomien, whilst English 

 geologists describe the Wealden and Lower Greensand as distinct formations. 



THE GAULT. 



In several coast-sections the Gault is seen separating the Lower from the Upper 

 Greensand ; this bed of dark clay is called " the blue slipper," from the tendency of the 

 overlying strata to form landslips by gliding over its surface. The charming scenery of 

 the Undercliff has been in a great measure produced by the foundering of the'Upper 

 Greensand and Cretaceous rocks over the Gault clay ; the rain-water having saturated these 

 porous beds, bursts forth in springs, which wet the surface of the clay, and occasions 

 slips of the superincumbent strata. A rich fertile soil is thus formed upon a broad terrace 

 of stiff clay, exposed to the south, and sheltered from the north by a high mural 

 escarpment of Upper Greensand. Under these favourable physical conditions vegetation 

 springs up in great luxuriance, on a natural terrace high above the sea, producing a 

 coast-scene unequalled in beauty in the British Isles. 



The Gault is about 100 feet in thickness, and in the Isle of Wight contains few fossils, 

 as Inocerainus sulcatus, Sow., and/, concentricus. Sow. ; near Folkstone and Charmouth it 

 lias yielded many beautifid shells in high preservation. I shall figure some rare Echinidce 

 from this bed at Folkstone. 



The Bed Chalk is a remarkable stratum, supposed to be the equivalent of the Gault ; 

 it is limited both in thickness and extent, for if we take, says the Rev.^T. Wiltshire, one 

 hundred feet as its maximum and four feet as its minimum thickness, and 100 miles as its 

 extreme length, we shall not be far from the truth. It is said to be peculiar to the English 

 Chalk. It is well exposed at Speeton, near Filey, on the Yorkshire coast, and at Hunstanton 

 Cliff, near Lynn, Norfolk ; in both localities it is a red calcareous rock, deeply coloured by 



