IN THE ANGLO-PARIS BASIN 43 



Bristow et al. (1889), Jukes-Browne (1900), and Osborne-White (1921) all give a 

 roughly uniform thickness of 100 feet (30-48 m.) for the Gault throughout the Island. 

 However, this is certainly not correct for although the thickness is about 100 feet 

 (30-48 m.) at Redcliff, it is reduced to about 65 feet (19-81 m.) at Compton Bay, and 

 may be over 100 feet (30-48 m.) in the southern part of the Island. Kitchin & 

 Pringle (1922 ; 160-161) recognised that Middle Albian sediments of the ' interruptus 

 Zone ' were present at Culver and in the south of the Island, but they considered that 

 the Gault in Compton Bay was wholly Upper Gault. They based their conclusion 

 on the old record of Inoceramus sulcatus (Norman 1887 ; 70), but it will be shown 

 below that this argument together with their view that the ' — so-called " Carstone " 

 of this locality — ' did not represent the true top of the Lower Greensand, is com- 

 pletely fallacious. Spath (1926b ; 422, and in Jackson 1939 ; 74) considered that the 

 Gault represented only the dentatus Zone and that the ' lower benettianus (=inaequin- 

 odum) zone ' passed into the Carstone beneath. This latter conclusion was confirmed 

 by Casey (1961a ; 515) based on material collected by C. W. Wright and the author. 



(a) Redcliff 



The Gault in the hollow between Redcliff and the Upper Greensand face at the W. 

 end of Culver Down (SZ 62758550) is badly slumped and overgrown. However, 

 from time to time exposures of a few feet of clay dipping steeply NE. have been seen 

 near the top and the base of the Formation. The Gault is here about 100 feet 

 (30-48 m.) thick but it is impossible at this time to obtain an accurate measurement. 

 From sections exposed near the base it can be seen that there is a fawn band within 

 six feet (1-828 m.) of the junction with the underlying pebbly Carstone. This fawn 

 band contains crushed Hopiites (H.) spp. with pyritic films replacing the shells, 

 together with a few part-phosphatised specimens. On the basis of the ammonites 

 so far seen, a basal spathi Subzone age is indicated. However, a similar unit at Bon- 

 church has yielded rare but definite lyelli Subzone fossils. 



Mr. J. McA. Hart collected a pyritised Euhoplites of Upper Gault aspect from a 

 small exposure near the top of the Gault and below Jukes-Browne's Division A. This 

 indicates that at Redcliff the lower part of the Upper Albian is within the clay facies. 



(b) Rookley 



Perhaps the most important section available in the Isle of Wight at this time is 

 exposed in the extensive workings of Island Bricks Ltd., at Rookley. The sequence 

 extends from well down in the Carstone up into the Gault and is shown graphically 

 in text-fig. 19. It has never been described in detail but has been mentioned by 

 Pritchett & Jackson (1941). The pit is cut by an E.-W. fault down-throwing to the 

 south, and the southern part of the section is tectonically disturbed. The sequence 

 north of the fault dips NW. at 6° and shows variations in the thickness of certain 

 beds which cannot be ascribed to a later tectonic cause. These are here considered 

 to be due to slumping before consolidation of the sediment. 



