AMMONITES — ZOOLOGICAL, ETC. 



west and east of France, the superposition of the inclosing 

 strata, and the order of succession of the same strata 

 I am able, without noticing the colour or the argilla- 

 ceous or siliceous nature of the rocks, to determine without 

 doubt by means of the Ammonites and the other animals 

 preserved with them : 1 st that there has been evidently three 

 grand geological periods, entirely separate and distinct, in the 

 cretaceous formation ; and 2ndly that each of these periods 

 had a separate and well characterised Fauna, especially 

 amongst the Ammonites found in each. 



§ 2. Division of the cretaceous formation into three distinct 



groups. 



To understand the generalisations which follow, I have 

 thought it advisable to explain the three grand divisions of 

 the cretaceous formation, such as I conceive them to be, 

 with their synonymes in different authors and languages. 



1st Group. Neocomien. — This is the Terrain cretace in- 

 ferieur of M. EUe de Beaumont; the Terrain Neocomien of 

 M. MontmoUin and the groupe inferieur of M. d'Archiac* 

 I divide it into two series of deposits. 



The Lower Neocomien, comprising the limestones, clay 

 a spatangues and blue marlsf of Haute Marne, Saint Dizier 

 and Wassy; the equivalent limestones of Vendeuvre, Ma- 

 roUe (Aube) and Neuchatel (Switzerland) ; the limestones 

 and marles of Girondas (Vaucluse), Saint Juhen (Flautes- 

 Alpes), Escragnolle, Lattes, Caussols (Var), Lagne, Castel- 

 lane, Cheiron, Sisteron, Robion, Bareme, Leons (Basses- 

 Alpes), Cassis (Bouches-du-Rhone), &c. &c. 



Upper Neocomien, comprising the upper marls of 

 Cassis (Bouches du Rhone), Vergons (Basses-Alpes) and 

 Gargas (Vaucluse) ; the clays ivith oysters and plicatulcB, 



* Perhaps the weald or weald day may form a portion of the Neocomien. 

 t These deposits have been described by M. Carnuel de Wassy. 



