18 THE INDIGENOUS FAUNA. 



be the case if the fossils of the one were derived from the 

 other 1 . 



Lastly, this belief in the indigenous character of many of the 

 vertebrates was greatly strengthened, and, indeed, became a con- 

 viction, when I again examined the lithological condition of the 

 bones; for most of .these are but slightly, if at all phosphatised, 

 but are impregnated with iron oxide; and yet these are the very 

 fossils which we should most certainly expect to be phosphatised, 

 both because of the presence of phosphate of lime in their original 

 composition and because of their many irregularities of surface 

 which are just the kind of spots where phosphatic matter is most 

 prone to accrete. 



But in examining a large series of the bones, I find that some 

 of them are phosphatised, and very thoroughly phosphatised too, 

 with here and there little masses of phosphatic matter adhering. 

 Examples of this may be seen in the Woodwardian Museum 

 amongst the Ichthyosaur vertebras; in the Pliosaurs (Case vi., a. 

 1 3), and in the Plesiosaurs ; (an example of the latter with ad- 

 herent phosphate may be seen in v. b. 4). It is these, and these 

 only, that are 'derived' fossils, washed out of the Jurassic 

 clays. 



I must here state that in an unassorted heap of the Potton bones 

 the truly derived phosphatised bones would form a much greater 

 proportion than in the cases of the Wood ward ia a Museum, for 

 these being the most worn and least well-conditioned of the 

 specimens, have been to a large extent picked out and rejected 

 from the better collections. 



Of the Cephalopoda we have but very scanty representatives 

 from the Upware and Brick hill beds, but these species are of great 

 interest and importance to us on account of their limited ranges in 

 space and time. Thus the Ammonites Cornuelianus is characteristic 

 of the Hythe beds of the south of England and of the Aptien of 

 southern Europe, and Am. Deshayesii is equally an Upper Neo- 



1 Exx. At Ely, in the Kimmeridge Clay, Gyrodus and Asteracanthua are the 

 most abundant fishes; other Ganoids, such as Ditaxiodus, &c., also occur, but 

 Sphairodus gigas is unknown. On the other hand, in the Neocomian, Ditaxiodus 

 and many other Kimmeridgian fish are unknown, and the Spharodus teeth are 

 some of the commonest fossils. The same argument is equally strong with the 

 Heptiles. 



