38 THE 'derived' fossils. 



In the subjoined table the principal species of the derived 

 Neocomian fossils are given, together with an account of their 

 distribution in space and time : — 



Ancyloceras gigas, Sby. Atherfield clay ; Aptien of Bedoule, Bouches 

 de Rhone (d'Orb.). 



Ammonites Cornuelianus, d'Orb. Aptien of Paris area ; Up ware, 

 Neocomian; Atherfield?; Hythe, Perte du Phone, Aptien ; Ber- 

 nese Alps. 



" A characteristic Aptien species," Pictet and Renevier. 



Ammonites Martini, d'Orb. Aptien, Paris area; Atherfield clay, 

 beds 12 — 29, Fitton (Forbes and Ibbetson); Constantine, Africa, 

 Upper Neocomian ; Beansset, Var. Up. Neocomian. 



Ammonites Deshayesii, Leym. Atherfield clay, beds 6 — 10, Fitton; 

 Aptien, Paris area ; Speeton, Upper Neocomian ; Brunswick, 

 Up. Neoc. ; Folkestone, Junction Bed ; Constantine, Africa ; 

 Beausset, Var. Up. Neoc; Pyrenees, urgo- Aptien. 



Perna Mulletti, Desh. Neocomian proper of Paris area ; in England 

 mostly in the Upper Neocomian, Atherfield clay, and Cement 

 beds of Speeton ; Tealby, Mid. Neocom. ; Schoeppenstedt, Lower 

 Neocomian ; Lander on, Lower Neocom. ; Switzerland, Valengien, 

 Urgonien. 



Perna Ricordiana, d'Orb. Neocomian proper of Paris area ; Ather- 

 field beds, Shanklin sands, St Croix, Perte du Rhone, Aptien. 



Thetis minor, Sby. Shanklin, Speeton, Upper Neocomian. 



Cardium subhillanum, Leym. Upware, Neocomian ; Neocom. proper 

 of Paris area ; Switzerland, Yalengien ; d'Arzier, Landeron, 

 Marnes d'Hauterive, Lower Neocomian. 



Trigonia ornata, d'Orb. Hythe ; Atherfield Perna bed ; Perte du 

 Rhone, Aptien. 



From this list we see that some of the derived species are 

 actually of late Neocomian or even Aptien age. But the indige- 

 nous fossils prove the Kodide beds themselves to be of Aptien age. 



The same kind of anomaly seems to exist in the Neocomian 

 rocks of Mont Saleve, where the fossils are casts of Neocomian 

 shells, &c, and the Serpula and Polyzoa have attached themselves 

 to the surfaces of these casts — a circumstance which M. de Loriol 

 states he is unable to explain 1 . 



Here then we are in a difficulty, for the history of a derived 

 fossil is usually a long and important one, identical indeed with 

 that of unconformity. We read its story as having lived its clay 

 in the seas of its birth, and been buried in the accumulation of 

 sediment, when the surrounding rock penetrated it and it became 



1 See de Loriol, p. 5, "Mont Saleve." 



