256 T, Davidson — Continental Geology. 



in the sequence of deposits, but these two breaks have not begun 

 or terminated at the same time. The Supra-jurassic deposit, in 

 which I was the first to show the existence of fresh-water fossils 

 (Comptes Eendus de I'Acad. des Sciences, Oct., 1849), might perhaps 

 have continued, whilst the first beds with T. janitor were being 

 deposited, but additional confirmation by renewed stratigraphical 

 and palaeontological researches will be required before we can fix 

 our ideas on the succession or partial synchronism of these breaks or 

 gaps, which are very evident, and call loudly for further research, 

 especially in the immediate parts between the Jura and the Alps." 



To his table of the Middle and Lower Cretaceous period [ante, p. 

 265), M. Pictet adds the following explanatory notes : — 



"No. 1. — Tithonic stage or limestone of Stramherg. I commence 

 my table (in the ascending order) by a stage of which the position 

 is still doubtful, thus raising one of the most controverted questions 

 of the day. On this subject there exists a misunderstanding between 

 M. Hebert and myself, but this disagreement has been much 

 exaggerated. The facts are as follows : M. Hebert was the first 

 to observe the Cretaceous aspect of the fauna of the Porte-de- 

 France ; to him therefore, incontrovertibly, belongs the merit of 

 having first drawn public attention to this fact. This observation 

 of M. Hebert's struck me the more forcibly from my having at the 

 same time had occasion to study the remarkable fauna of Berrias, 

 and that I found therein the confirmation of M. Hebert's idea 

 of the existence of Neocomien faunas more ancient than those 

 already known. I believe I was the first to determine that the 

 section of the Porte-de-France contains three different stages. The 

 Jurassic, at the base, the true Neocomien at the top, and the Stram- 

 berg limestone in the middle. In the first instance I was cen- 

 sured for seeking to establish comparisons with the deposits of 

 the Carpathians ; subsequently, the necessity of so doing has been 

 acknowledged, so much so indeed, that the only question now at 

 issue, is that of determining the age of the Stramberg limestone 

 (no one disputes its identity with the limestone of Aizy), 



" In the table published (Melanges Paleontologiques, 4th decade) 

 I traced a line A which separates the Stramberg limestone from the 

 underlying Jurassic period, and another line B which separates it 

 from the limestone of Berrias situated above. I then suggested that 

 the boundary of the Jurassic period was either on the line A or on 

 the line B, or between the two. M. Hebert accepts the line A as 

 the separation. We were no longer agreed when it was necessary 

 to come to a definite understanding. M. Hebert thinks the question 

 has been sufficiently answered, and admits without reservation 

 that the Stramberg limestone belongs to the Neocomien period. I 

 cannot so speedily arrive at that conclusion ; I recommend more 

 study, and require further evidence ere I decide. 



"I coincide in his opinion that the evidence derived from the 

 Cephalopoda is in favour of the idea that the Stramberg limestone 

 is Cretaceous. Since the valuable researches of M. Zittel there 

 is an increased analogy, a striking one, between Stramberg and the 



