258 T. Davidson — Continental Geology. 



magnificent fauna characterised by the unrolled Cephalopoda of the 

 South, which very nearly corresponds to the Barremien of M. 

 Coquand. Belem. dilatatus, Amm. tetJiys, A. Bouyanus, etc. Ancy- 

 loceras Emerici, A. TabarelU, etc. Tereh. diphjoides, etc. 



" No. 5. — JJrgonien. Well characterized in the Swiss Jura, and 

 having a closer connection with the yellow stone of Neufchatel than 

 any other Aptien stage. It is questioned by some French geologists, 

 because in certain southern localities of the basin of the Ehone it is 

 reduced to beds, but slightly characteristic, containing Orbitolites, 

 which elsewhere are strictly Aptien. In the Jura it forms two 

 stages ; the lowest is the richest. The forementioned memoir of M. 

 Jaccard (map of Switzerland) contains a list of upwards of 120 

 species (Nerinea orbensis, N. Crozetensis, Pleurotomaria orhensis, 

 Pygunis productus, Heteraster Couloni, etc.). The upper stage, in 

 the Jura, seems exactly parallel with the limestone of Orgon, and 

 contains the same Caprotince, Lima Orbignyana, etc. 



"No. 6. — Aptien. A stage entirely distinct from the JJrgonien in 

 Switzerland. It forms two beds, inseparable on account of the great 

 number of species common to both. The lower or Bhodanien 

 (Amm. Martini, A. f meatus, A. Campichei, A. Desliayesi, etc. Bel. 

 semicanaliculatus, etc.) possesses a numerous fauna (see our publica- 

 tions). The upper bed is composed of hard green sandstones, and has 

 a close resemblance to the Gault and is parallel to the bed con- 

 taining Ostrea aquila. These two beds, upon the whole, exactly 

 correspond to the Lower Green Sand, a fact proved and established 

 by us long since. 



" According to our views, there is consequently in the South of 

 England no Cretaceous deposit more ancient than our Aptien. As 

 to the Speeton Clay, it is impossible for us to have an exact idea of 

 it, notwithstanding Mr. Judd's description. It is necessary that a 

 paper, accompanied by good plates, should replace, by its clear 

 evidence, those catalogues replete with references to unpublished or 

 little known species. Pray use your influence to induce Mr. Judd 

 to render science the important service of completing this work.^ 



"No. 7. — Gault. The true Gault of Folkstone of the Yonne and 

 the Aube is represented with us sometimes by one and sometimes by 

 two beds, designated by the names of Lower and Middle Gault. It 

 is rich in fossils. 



"No. 8. — Upper Gault presents various aspects. In the Swiss 

 Jura it is a mixture of species found in the Gault {Amm. inflatus, A. 

 Velledce) with forms ordinarily more recent (Pecten asper, etc.), 

 and with some new species. It is the Vraconien of M. Eenevier. 

 In the Alps of the Canton de Vaud (Col de Cheville) an association 

 tolerably similar is found very distinct from the Lower Gault. In 

 the Alps of Savoy, on the contrary, there is frequently a mixture of 

 species belonging to the Lower and the Upper Gault. The Vraconien 

 appears to us entirely contemporaneous with the Upper Gault of 



1 Mr. Judd informs me that he has at present in preparation descriptions accom- 

 panied by illustrations of the species which occur in the beds of the Speeton Clay, 

 so that M. Pictet's earnest request will shortly be complied with. 



