225 



taille ne permet de I'obtenir que rarement entier. L'ooUthe 

 n'etant pas speciale a cette sub-division, j'ai cru devoir adopter 

 le nom de Diceratien." 



M. Btjvigniek, in 1852, and M. Ed. Piette, in 1857, liave 

 made important works on tlie department of the Meuse, the 

 "Calcaire a Astartes de Verdun" forme a la partie superieure de 

 calcaires blancs crayeux, quelquefois gris marno-compactes ; et a 

 la partie inferieure d'argiles grises on jaunatres assez passantes, 

 avec Ostrea Bruntrutana,Astarte minima, Melania striata, Geromya 

 inflata, Cardium Buvigineri. This formation attains here a 

 thickness of 130 metres and rests upon the coral rag de St. 

 Mihel, consisting of white chalky Limestones of great purity, 

 containing Nerinoea Bruntrutana, N. nodosa, and Diceras arietina 

 in its upper portions ; Ostrea gregaria, Cidaris BlumenhacUi, 

 Hemicidaris crenularis, Thamnastrcea affinis, Calamophyllia flabel- 

 lum, and Gal. articulosa in its lower division. The coral rag 

 attains a thickness of 130 metres = 400 feet. 



S^QTJANIEN. 



The Sequanien or Nerincen zone, which forms so important a 

 member of the CoraUian series in France and Switzerland, is 

 not represented in England. The fine white Limestones, for 

 the most part, composing these rocks are formed of the debris 

 of coral-reefs that played so important a part in the seas of the 

 upper Jurassic epoch; and if strata synchronous with those 

 forming this stage ever existed in our area they have been 

 eroded and subsequently removed from English soil by denu- 

 dation. This fact affords a good illustration of an observation 

 previously made in reference to the existence and development 

 of different zones of the Lias and Lower Oolites. In some 

 locahties, for example, we find certain terrains largely thickened 

 and containing few characteristic fossils ; in others the zone may 

 be absent, or present and feebly developed, and the thin rudi- 

 mentary beds composing it may be largely charged with their 

 leading shells ; so that in studying the Jui-assic formations, with 

 a view to establish their synchronism, it is on the palaeontology 



R 2 



