the Limits of the Jurassic and Cretaceous Periods. 323 



facts, I obtained for the Bibliotheque Universelle a notice* which 

 formed the primary basis of the discussions in which I have taken 

 part, and which have repeatedly occupied the Geological Society 

 of France. 



The principal object of this note was to establish, in the first 

 place, the existence of the inferior limestones already mentioned, 

 which carry the origin of the Cretaceous period to a more ancient 

 epoch than had been supposed. Then passing to the investiga- 

 tion of the limestones of the Porte-de- France, the section of 

 which was well known from the excellent works of M. Lory, 

 M. Hebert came to the conclusion, from exclusively palseontolo- 

 gical considerations, that these limestones should be ascribed to 

 the Neocomian period, and not to the Oxfordian stage, as they 

 usually had been. 



Our learned friend founds his conclusions upon the investiga- 

 tion of fossils communicated by MM. Lory and Chaper, and 

 cites, as an important character of these beds, the presence of 

 Terebratula diphya, which, according to him, is incontestably 

 Neocomian and only forms a single species; for, he says, the 

 most careful examination does not enable us to find the smallest 

 constant specific character between this and T. diphyoidesf. 



This novel and bold opinion as to the age of the Terebratula- 

 diphya limestones of the Porte-de-France was received with some 

 astonishment, and became immediately the subject of discussions. 

 I must explain in a few words how I was led to mix myself up 

 in them. I one day received a visit from Brother Euthymus, 

 who brought me a series of fossils from Berrias, in which I 

 speedily recognized a fauna with Neocomian characters, but 

 consisting for the most part of unknown species. Brother Eu- 

 thymus was kind enough to accompany me into the department 

 of the Ardeche ; and then, thanks to the assistance of the autho- 

 rities of Privas, and to investigations made at Berrias itself under 

 the auspices of M. de Malbos, I was able to publish a monograph 

 on the Limestone with Terebratula diphyoides of Berrias J, and 

 thus to add, to the first discovery of M. Hebert, the description 

 of a Neocomian fauna of greater antiquity than any of those 

 then known. 



* Hebert, " Sur les limites de la periode Jurassique et de la periode 

 Cretacee, et specialement sur les calcaires a Terebratula diphya," Bibl. Univ., 

 Arch., August 1866. A similar notice was published in 1869 in the 

 Comptes Rendus, vol. lxiv. p. 1053 ; this was completed by a second note 

 in the Bull, de laSoc. Geol. 1867, vol. xxiv. p. 389. 



t In his subsequent works, M. Hebert has been less positive ; and if I 

 here repeat his first assertion, which has since been much softened, it is 

 solely to show the necessity of a monograph upon the Terebratula of the 

 diphya-grou\). 



X Melanges paleontologiques, 2 me livr. vol. i. p. 41. 



Y2 



