T. Davidson — Notes on Continental Geology. 301 



plete their views I now publish a letter recently received from M. 

 Hebert, which he requests me to add to the present notes. 



" Paris, l^th May 1 869. 



M. Pictet, who maintains the utmost courtesy in our discussions, communicated to 

 me some time ago an extract of the opinion he sent you regarding' the linicslone with, 

 Ter. diphi/a. It seems necessary in my turn to address you for the sole purpose of 

 stating my opinion precisely. It shall be a short one, repeating very nearly what you 

 will find in the Bulletin of the meeting of the 9th Nov., 1868, p. 138, and which will 

 be speedily forwarded to you. If you read what I have published upon this question 

 you will observe that I have hitherto only drawn up conclusions concerning the 

 limestones lolth Ter. diphya ov jnnitor of the Porte-de- France and those of Aizy which 

 contain the same fauna. This fauna, composed in a great measure of Oepluilopoda, is, 

 to my mind, certainly Neocomiun. The more I study the question the fewer are the 

 doubts I have on this subject, because I find a greater number of species really 

 Neocomian. But in the limestones with Cephalopoda there is intercalated at Aizy a 

 thin bed of small extent, disappearing at a little distance, containing a mixture of this 

 fauna with another which resembles the Coralline fauna. In like manner at Stram- 

 berg to the fauna with Neocomian Cephalopoda., of the Porte-de- France, is made the 

 addition of iJiceras, of Brachipoda and of Nerincea, which had until now seemed 

 identical with Coralline species. This portion of the fauna of Stramberg does not 

 exist at the Porte-de- France, but is found identically the same at Inwald (Galicia), 

 at Saleve, at Echaillon, in the lower Alps, and in the Gard ; but in all these localities 

 of the Carpathians, of Switzerland, of the Dauphine, and of Provence, this Coralline 

 fauna has hitherto included none of the Neocomian Cephalopoda of the Porte-de- 

 France, or of Stramberg ; this remark ought not to be lost sight of by Geologists. 



It is true that a more attentive examination has singularly reduced the number of 

 identities admitted between this Coi-alline fauna and the veritable Coral Hag of the 

 north and of the Jura ; but we must not forget that the reputed Jurassic species are not 

 found either at Aizy, or at Stramberg, save in those beds that are true breccias 

 resulting from the destruction of an older deposit. Therefore the question concern- 

 ing the limestone with Cephalopoda appears to me as much settled, as the question 

 regarding the beds with Diceras and Nerincea seem to me to be obscure. In fact, Ave 

 do not yet know very positively if there is a single form identical with the Jurassic 

 species. In the case of some identities still maintained we do not know whether they 

 are contemporaneous with the deposit, or are species which have been introduced 

 from a lower bed. We have now to study this curious fauna of Inwald, of Echaillon, 

 of Saleve, of the Serane (Gard). The most complete collections from these formations 

 have been generously placed at my disposal by Messrs. Zejszner, Lory, Pillet, Wallet, 

 and Jeanjean. Shall 1 have leisure and capability to derive therefrom a correspond- 

 ing advantage ? That is the question. 



Anyhow it is certain that from the Carpathians to Montpellier the beds with 

 Terebratula Moravica (Glock) constitute a stage distinct from the limestone with 

 Tereb. diphya, ov janitor, that we shall probably be able to observe in the south of 

 France the stratigraphical relation of the two systems, and from notes recently sent to 

 the Geological Society by M. Coquand, I can almost deduce that Tereb. Moravica 

 is regularly inferior to 2'ereb. janitor. This, however, is not asserted decidedly as yet. 



Pray inform your English colleagues that I have proceeded with the greatest 

 caution, and that I have confined my observations to the beds with Tereb. diphya. 

 These are the ones I have considered to be Neocomian. I have brought forward 

 nothing in regard to the position of the formation wiih Tereb. Moravica. I am 

 doubtful of the latter belonging to the Coralline period, but I know nothing of it. 

 This to me is the actual horn of the problem. Cppel had referred to the Titonic 

 formation, the Portland limestone, the beds of Boulogne, of Solenhofen, Nattheira, 

 etc. Zittel, on the contrary, rejects with good reason all these from the 'J'itonic 

 stage, and I think we must also eliminate the limestone with Tereb. diphya as 

 Titonic ; there consequently only remains the limestone with Tereb. Moravica, which 

 really appears to me very curious ; but I cannot as yet pronounce upon its age 

 decisively. These explanations will show you that M. Pictet and I are very close 

 upon a mutual understanding, since the objections of my eminent colleague and friend 

 rest now almost entirely upon the fauna of the bed containing Tereb. Moravica, and 

 that I consider it in no way demonstrated that the fossils of these beds are con- 

 temporaneous with those containing Tereb. Janitor." 



