A. PAVLOW — MARINE MESOZOIC FORMATIONS. 61 



The second paper read was : 



ON THE MARINE BEDS CLOSING THE JURASSIC AND OPENING THE CRETA- 

 CEOUS, WITH THE HISTORY OF THEIR FAUNA. 



BY PROFESSOR ALEXIS PAVLOW, OP THE UNIVERSITY OF MOSCOW, RUSSIA. 



As regards the Paleozoic system, comparative or systematic geology has recently 

 made great progress, thanks to the excellent work of American and European geol- 

 ogists ; the correspondence of stages in the two continents has been established, and 

 the history of the Paleozoic seas is, in its principal features, the same for the whole 

 northern hemisphere. The case is different for the Mesozoic beds, especially for 

 those that close the Jurassic system and begin the Cretaceous. A kind of separat- 

 ism is observed in them : In the Anglo-Parisian basin and in part in Germany the 

 upper stage of the Jura is called by the name of Portlandian, and the Cretaceous is 

 held to begin with the Neocomian ; in the southern part of France, in Spain, and 

 in the Alps it is the Tithonic stage that tops the Jurassic, and the Tithonic in its 

 turn is overlain by the Berrias ; in northern England the boundary between the 

 two systems passes through a series of beds called the Speeton clay ; in Russia, the 

 name of Volgian stage has been created to designate the upper beds of the Jura 

 and the lower beds of the Cretaceous. Every country claims at this epoch its pe- 

 culiar geologic history, and the geologists of the various countries are busy describ- 

 ing the peculiarities of the beds deposited at that epoch. But what has become of 

 the vast ocean of the globe as it then existed ? Do we know the faunal history of 

 that ocean, a history independent of the local episodes spoken of in describing 

 these stages? What has become of the cephalopoda, the ammonites and the 

 belemnites, our faithful guide in the parallelization of the Mesozoic beds? These 

 are the questions that have long interested me, and I am happy to be able to com- 

 municate to this distinguished Society some results of my studies. 



I shall try to be brief. I am convinced that the separatism of which I spoke is 

 not a consequence of the minute comparison of these stages, but rather a result of 

 the lack of comparative study, of the absence of a well concerted synonymy of the 

 species, and of the incompleteness of researches on the development of the faunas. 

 I have undertaken this study for belemnites and the ammonites, and the results 

 which I am going to set forth will demonstrate, I hope, its importance for strati- 

 graphic questions. 



I had at my disposal, in my studies, a large collection from Speeton and Lincoln- 

 shire, by Mr. Lamplugh, the collections of the museums of York and Scarboro, some 

 forms from the South Kensington Museum and from the museum of the Jardin 

 des Plantes at Paris, and a large collection of fossils preserved at the museum of 

 Moscow. 



In studying minutely the characters of the belemnites of the groups Excentrici and 

 Absoluti, and of the English group Oweni, which arc the most numerous in the beds 

 spoken of, I was able to distinguish amongthem three great brandies, each develop- 

 ing in a certain direction. The neighboring species that enter into these branches 

 pass insensibly into one another, so that the limits between them are more or less 

 arbitrary, while in the case of the typical forms they are perfectly well distinguished. 

 The most interesting fact from a geologic point of view is that these branches, in 

 the various countries, pass through beds developing in a parallel manner, and we 

 observe iii England and in Russia that the same phases of development appear 



