230 B^vieios — Fictet's. Jurassic and Cretaceous Bocks. 



I. — On the Limits of the Jurassic and Cketaceojjs Formations. 

 By F. J. Pictet. 



[Rapport fait a la session de 1869 de la Society Helvetique des Sciences Naturelles.] 



IT lias been generally admitted that the Kimmeridgian and Port- 

 landian stages form everywhere the upper limit of the Jurassic 

 period, and that the Neocomian (including the Valangian stage) form 

 the lower limit of the Cretaceous period. These limits appear 

 reasonable from the existence of intermediate freshwater deposits 

 (Wealden). 



Late researches have tended to render somewhat indefinite th.e 

 boundary between these peiiods, and numerous discussions have 

 taken place, of which the author gives a resume in the present 

 sketch. 



Oppel, in 1865, determined the existence of certain strata, charac- 

 terised by a very rich fauna, between the upper Jurassic (Kimme- 

 ridgian stage) and the Neocomian, to which he applied the name 

 Tithoriic. 



The succession of the beds is not contested. Numerous published 

 works show the succession of faunas has been the same at many 

 points far distant from one another, and it may be considered as a 

 fact that from the Carpathians to the Mediterranean, in all places 

 where the Tithonic stage has been met with, the series is disposed 

 as follows : — 



1. Neocomian stage (proper). 



2. Valangian stage, and Marls with Belemnites Idtus.. 



3. Limestone of Bemas. 



4. Tithonic stage. 



5. Bed with large specimens of Aptychws. 



6. Jurassic fauna with Ammonites tenuildbatus. 



The limit of the Jurassic and Cretaceous periods may be drawn 

 between stages 4 and 5, or between 5 and 6. But M. Pictet asks, 

 is it not possible that there has been no interruption between the 

 two periods? 



The question, he maintains, can only be solved by a general com- 

 parison of the beds in question over a large area. 



Reviewing the researches of Palseontologists in various localities, 

 he gives the following arrangement to show the succession of beds 

 where the Tithonic stage is well developed : — 



1. Lower Neocomian stage and Limestone of Berrias {Terehrcvtula 



diphyoides). 



2. Upper Tithonic fauna, or Limestone of Stramberg (Terehratula 



Janitor). 

 S. Lower Tithonic fauna of Eogoznik, Blue Marble of the 



Apennines, and probably the Limestone with Terebratula, 



diphya of the Tyrol. 

 4. Fauna with Ammonites tenuiloiatus. 



Nos. 3 and 4 have characters eminently Jurassic ; No. 2 is rather 

 Cretaceous ; and in No. 4 are found the usual forms of this period. 



