Geology and Physiography ii 



around Haddenham. The upper part of the Kitneridge Clay is absent, the 

 Lower Greensand resting unconformably on it. At Upware, a few feet 

 of Kimeridge Clay (exact age unknown) wedges out under the Lower 

 Greensand against the CoraUian ridge. Lithologically, the Kimeridge 

 Clay is distinguished from the other Jurassic Clays by the presence of 

 paper shales. Near Southery in West Norfolk, Dr Arkell records, from 

 borings, thicknesses of about 145 ft. of Kimeridge Clay, but the faunal 

 succession is incomplete. 



THE LOWER GREENSAND 



The Lower Greensand, largely covered by drift, extends from Gamlingay 

 in a north-easterly direction to the Fenland, where it caps the ridges at 

 Haddenham and Ely; outcrops are also found upon the flank of the 

 Upware- Wicken ridge. It is an important water-bearing formation. The 

 best exposure is to the south-west of the County boundary at Sandy 

 (Beds), where strongly false-bedded, yellow sands occur; and, about 

 100 ft. above the base, a pebble bed has been recorded containing derived 

 ammonites {Pavlovia spp.) characteristic of the Hartwell Clay. At Upware, 

 the Lower Greensand is represented by about 12 ft. of yellow sand, with 

 a basal conglomerate with layers of phosphatic nodules; this oversteps the 

 Kimeridge Clay on to the Corallian. The rare Aptian ammonites at Upware 

 include phosphatised fme-grained internal casts, which Keeping suggested 

 were derived ; they are identified by Dr Spath as species of Deshayesites, 

 characteristic of the upper Lower Aptian. There are also a few forms, with 

 the shell preserved round a sandstone matrix, which are possibly indigenous. 

 Unfortunately these caimot be determined with certainty, but Dr Spath 

 compares them with Columbiceras which is said to occur elsewhere in the 

 lower Upper Aptian. A badly preserved internal cast of ?Tropaenm sp., 

 identified by Keeping as Ancyloceras hillsi, contains a similar matrix. 



Keeping attempted to identify the various derived fossils found in the 

 Lower Greensand of Upware, Potton and Sandy, and he claimed that 

 Wealden, Neocoiruan, Portlandian, Kimeridgian, Corallian and Ox- 

 fordian forms are to be found. His identifications, especially those of the 

 ammonites, are, however, in need of revision. Since the Lower Greensand 

 rests in different places on Oxford Clay, Ampthill Clay, the Upware 

 Corallian and Kimeridge Clay, fossils derived from these formations 

 are to be expected. A Carboniferous trilobite has been found at Sandy, 

 and fossils identified as of Lower Palaeozoic age at Potton (Beds). 



The indigenous fossils at Upware included abundant porifera, polyzoa, 

 lamellibranchs, and especially brachiopods. The bracliiopods of Brickhill 



