72 MIDDLE ALBIAN STRATIGRAPHY 



probably present at Winchester, and may well be present in the unexposed lowest 

 part of the Gault at Selborne in the western Weald in view of the close similarity 

 which exists in the detailed lithological sequence between this locality and the Horton 

 Clay pit, Upper Beeding (text-fig. 14). Sediments of this Subzone are known to 

 intervene between the ' Iron Grit ' and the spathi Subzone sediments along the out- 

 crop between Nyewood and Storrington, but they are thin and gritty (p. 34). In the 

 southern part of the Isle of Wight, however, sediments of this age are again compar- 

 atively well developed. The spathi Subzone sequence recognised at Selborne thins 

 southwards to Nyewood but lithologically it remains the same (Owen 1963a & text- 

 fig. 30). In the Isle of Wight, however, the sediment sequence is quite different. In 

 the absence of sections it is not possible at this time to determine whether the Ports- 

 down swell affected deposition during later Middle Albian Subzones. 



It is becoming apparent that the thinning of the Lower Greensand and the Gault 

 at Compton Bay relates to yet another ' swell ', probably that indicated by the 

 Ringwood gravity high, evidence of which is provided by the British Petroleum Co., 

 borings at Fordingbridge, Hants (Falcon & Kent i960 ; 48-49), and Bere Regis, 

 Dorset (Falcon & Kent i960 ; 7), in which the Gault was found to rest directly upon 

 the Kimmeridge and Oxford Clays respectively. 



(ii) LONDON BASIN, EAST ANGLIA, AND KENT 

 (a) London Basin, S. Essex & N. Kent 



Borings north of the Thames at Canvey Island (Smart, Sabine & Bullerwell et al., 

 1964) Fobbing (Dewey et al., 1925) Beckton Gasworks No. 4 (Barrow & Wills 1913), 

 Essex ; Tottenham Court Road (Prestwich 1878, Judd 1884), Willesden No. 1 (Falcon 

 & Kent i960 ; 15), London ; and Bushey, Hertfordshire, provide evidence that the 

 Upper Gault rests directly upon either the Palaeozoic rocks of the Mesozoic floor or 

 upon a thin development of Jurassic or Lower Greensand sediments. However, in 

 the Gas Council Cliffe group of borings encompassing the area of the East Tilbury 

 Marshes, Essex, and across the Thames in the Cliffe and Higham parishes of Kent, 

 Middle Albian sediments are represented in a sequence closely comparable to that 

 seen in the Lower Gault of the Maidstone By-Pass (p. 18), and, moreover, they show 

 no sign of either a land area or submarine cliff only a few miles to the north. 



The Lower Gault of the Cliffe group of borings rests upon a thin development of 

 Lower Greensand which in turn rests upon Oxford Clay preserved in a late Jurassic- 

 early Cretaceous graben structure, or in the case of the two most southerly borings 

 upon Devonian sediments as at Canvey Island and Fobbing situated to the north of 

 the graben. The stratigraphy of these borings, the structure of the area, and its 

 tectonic history, are discussed more fully elsewhere (Owen in press) . In this work it 

 is concluded that the absence of Lower Gault over much of the area north of the 

 Thames in London and South Essex, is due to a further movement of the northern 

 fault of this graben in early Upper Albian times. 



Further west in northern Surrey, three borings have yielded information about 

 Middle Albian sediments. These are located at Addington, Richmond and Egham 



