PRESTWICH BRITISH AND FOREIGN TERTIARIES. 225 



larger lists of the Calcaire grossier fossils, it is principally the new 

 and peculiar species of these lower strata which remain to be 

 described. 



Further, to take the " Lignites" as subordinate to the " Glauconie 

 inferieure." From M. Graves's list of the shells belonging to the 

 Oise "Lignites," including those of the Aisne of M. d'Archiac, we 

 obtain the following data* : — 



Range 

 Total. upwards. Peculiar. 

 Fossils of the Lignites 



and associated clays .. . 37 14 23 



Adding to these three additional species found in 

 the Rheims district t, and three new species re- 

 cently described by M. Watelet from Soissons ... 6 



29, — or 78 per cent. 



If we add these numbers to those before obtained of the fossils of 

 the lower Sands of the Oise and Champagne, the following will be an 

 approximate result of the distribution of the fauna of these strata, — 

 those included in the three lowest divisions of M. d'Archiac : — 



Total of Species ranging Species peculiar Per-centage of 

 species. upwards. to the series. peculiar species. 

 152 55 97 64 



only 36 per cent, of the known species thus ranging up into the beds 

 above these divisions. The independence of this fauna, although not 

 appearing at present so great as I believe it will be ultimately found, 

 is nevertheless important, and furnishes us with sufficient data for 

 the subsequent argument. 



The generally excellent state of preservation of the fossils of 

 the Lits Coquilliers, their abundance, and the large proportion of 

 described species | afford us much better means of judging of the 

 fauna of that period. They have been made the subject of especial 

 research by M. d'Archiac, M. Melleville, and M. Graves, in whose 

 works we find large and carefully drawn up lists, and by whom the 

 position of these beds in the geological series has been accurately 

 determined ; the only question about which there is, as before- 

 mentioned, a difference of opinion amongst the French geologists, 

 being as to whether this deposit should be grouped with the beds 

 beneath or with those above it. The following table, showing the 

 range and distribution of the Mollusks found in the Lits Coquilliers 



* I do not include in this list the very remarkable land and freshwater shells 

 of Rilly, as they form too exceptional a group to be used as a term of comparison. 

 M. de Boissy has described and figured thirty-nine species, all peculiar to these 

 beds (Mem. Soc. Geol. de France, 2 ser. vol. iii. p. 257, 1848). This deposit I 

 consider subordinate to the Lignite series ; M. Hebert places it lower, or under 

 the marine sands of Rheims. In either case, however, it would belong to this 

 lower eocene series. 



f Soc. Hist. Arch, et Scient. de Soissons, 1851. 



X M. Deshayes has described and figured the greater number of the fossils of 

 Retheuil, Pierrefonds, and Cuise-La-Motte in his valuable " Description des 

 Coquilles fossiles des Environs de Paris." M. Melleville has, however, since de- 

 scribed a considerable number of new species (pp. cit.) 



VOL. XI. — PART I. R 



