the Limits of the Jurassic and Cretaceous Periods. 325 



Berrias probably represents an horizon immediately below our 

 Valangian. In the Department of the Bouches-du-Rhone M. 

 Coquand has found this Berrias limestone immediately covered 

 by the bed with Natica leviathan, a fossil characteristic of the 

 Lower Valangian. 



Thus it will be seen that the great features of the question 

 were pretty well sketched out in these first works. It remains 

 for us to see what has been its subsequent development. 



Every one now seems to be nearly agreed as to the facts which 

 we have just related. The succession of the formations is not 

 contested ; and it is useless to refer here to some divergences of 

 detail which do not in any way affect the general solution of the 

 question*. 



Numerous works published of late years show that this succes- 

 sion of faunas has been the same at many points distant from 

 each other. MM. von Hauer, Suess, Zittel, Benecke, Mojsisovics, 

 Neumayr, &c. have ascertained facts remarkably in accordance 

 with those which I have just indicated ; and we may regard it as 

 a settled point that from the Carpathians to the Mediterranean, 

 wherever the Tithonian formation is met with, the stages are 

 usually arranged in conformity with the following section : — 



1 . Neocomian stage, properly so called. 



2. Valangian stage, and marls with Belemnites latus. 



3. Berrias limestone. 



4. Tithonian stage. 



5. Bed with large Aptychi. 



6. Jurassic fauna with Ammonites tenuilobatus. 



The principal question, that of the limit of the Jurassic and 

 Cretaceous periods, may therefore be presented here as the alter- 

 native between the following solutions. 



The line of separation may be the line A of my memoir — that 

 is to say, the line passing between Nos. 4 and 5. 



It may be drawn a little lower — that is to say, between Nos. 5 

 and 6. 



This line of separation may also be the line B of my memoir, 

 and pass between Nos. 3 and 4. 



* In particular M. Hebert and myself have not always interpreted the 

 species in the same way. For my own part I persist in the greater part of 

 my determinations, but I must remark that these differences of apprecia- 

 tion cannot at all modify the results indicated. Moreover it would be easy 

 for me to show that the signification of my assertions has often been too. 

 much extended. Thus, when I proved (with MM. Bayle and Chaper) that 

 Ammonites Stazyscii and A. Liebigi&re not A. Grasianus and subfimbriatus, 

 I was told in reply that these two species pass into the Neocomian, which 

 I have never denied: and so forth. 



