DERIVED FOSSILS. 155 



The matrix in all the known localities, except Upware, appears 

 to be similar, namely, a hard green-grey sandstone most like the 

 hard consolidated masses in the Lowest Cretaceous Sands of Lin- 

 colnshire. 



At Upware it occurs as internal casts in a compact earthy 

 phosphate of lime, often much rolled and penetrated by boring- 

 bivalves. 



Localities. Upware, Brickhill, Potton. 



In the gravels and drift of Suffolk and Norfolk. 



Also in boulders in Lincolnshire (S. Willingham), and West 

 Dereham ; Downham Market ; Ely ; also Feltwell in Norfolk. 



C. Derived Fossils belonging originally to the 

 Jurassic Age. 



(See ante, pp. 41 — 46.) 



(They occur as a rule in a phosphatised and much rolled 



condition.) 



Belemnites explanatus, Phillips. Monog. Behmnites, Pal. Society, 



t. xxxvi., figs. 94—96, p. 128. 



In the alveolar cavities groups of Serpula tricar inata (a Jurassic 

 fussil) are found adhering. 



The species is abundant in the Ampthill Clay, and in the 

 Kimmeridge Clay of Hartwell, Wheatley, &c. 



Locality. Upware. 



Ammonites giganteus, Sby. ? 



Fragments of very large Ammonites which probably belong to 

 this species are found in the Brickhill area. 



Ammonites biplex, Sowerby. 



(Plate viii., fig. 11.) 



Typical forms of this species abound in all the Neocomian 

 phosphatic deposits of Cambridgeshire and Bedfordshire, and they 

 are also conspicuous in the similar beds in Lincolnshire. In some 

 of the pits, especially near Brickhill, they actually form a large 

 proportion of the heaps of phosphatic nodules. They. are invariably 



