326 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Pecten quinquecostatus. Trigonia divaricata, d^Orb, 



Pterodonta, d'Orb. Unio Martini, d'Orb. 



Rostellaria Robinaldina. ? Ammonites Desliayesii. 

 Trigonia caudata, Agassiz. 



The group called Argile a Plicatules, in M. Cornuel's section, 

 nearly agrees I believe witli the Terrain Aptien of M. d'Orbigny, 

 which the latter conceives to constitute a well-marked and perma- 

 nent division in the subcretaceous series. But in the Atherfield 

 section the only Plicatula that has been found appears at the bottom 

 in the lowest Perna group ; and if the species in the following list, 

 which comes to me from Mr. Morris, be characteristic of this pro- 

 posed division, its universal prevalence is more than doubtful, since 

 a great majority of the species are found, almost exclusively, in the 

 much lower members of our section, and some of them only there. 



" T^rain Aj)tien." ^^"^^^ of occurrence near Atherfield. 



Astarte sinuata ? Lower Perna bed. 



Panopsea Prevostii, Atherfield clay. 



Mactra Carteroni. Specimens from the Crackers' group No. 4 have been 



Thetis laevigata. thus named by M. d'Orbigny. Species of the genus 



(Thetis) pervade the whole section from No. 1 

 to 45. 



Corbula striatula. Lower Perna bed. 



Gervillia linguloides. In No. 4 of ' the Crackers * group. 



Forbesiana {solenoi- In the upper Perna bed, Atherfield clay, and * Crackers* 



des of Geol. Mus.). group. 



Jvima Cottaldina. Upper Perna bed, and upper part of * Crackers ' in 



9-10. 



Natica Cornueliana. In ba, lower nodules of ' the Crackers ' group. 



Ammonites Martini. In the sand (18) of the lower Crioceras group. 



Deshayesii. Found principally in the lower part of the section from 



2 to 9, the Perna group and ' Crackers ;' also in 

 15, with Scaphites, and in 34a of the upper Cri- 

 oceras group. 



I have already intimated the general grounds on which it might 

 be questioned whether any natural subdivisions do universally exist : 

 the argument derivable from the facts just stated would be, that, ad- 

 mitting such a division to be discoverable, the assigned species are 

 not characteristic of it. 



The true relations of the strata near Vassy, between the lower 

 "Marnes" of M. Cornuel and the representative of the Portland 

 stone, have been a subject of difficulty to the author himself; and I 

 cannot help thinking that these strata really represent a part of our 

 Purbeck series, — the lowest member of the Wealden ; — which would 

 increase the probability that the ferruginous sands above them belong 

 to those of Hastings. M. Cornuel states that there is a discordance of 

 stratification between the list of questionable beds, which he calls *' ter- 

 rain suprajurassique,^' and those of Portland ; and the principal species 

 which he assigns to his "oolite vacuolaire^^"" is a Cyrena, of which 



* It may be mentioned, as an empirical point of resemblance, that an oolitic 

 stone which has very much the general character oi freshwater limestone, and in 



