548 PROF. PAVLOW Otf THE CLASSIFICATION" OF THE [Aug. 1 896, 



The scheme illustrated in the accompanying Table has been drawn 

 up to illustrate the correlations of the beds above discussed, in the 

 light of our present knowledge. Naturally, I have found it possible 

 to give more details regarding the Russian than the foreign beds. 



In Russian literature the name ' Volgian ' stage or stages is still 

 applied to designate certain beds of the series in question, namely 

 the beds ranging from the virgatus-zone of Portland to the nodiger- 

 zone of the Aquilonian. Many other divisions of our series have 

 been supposed to be contemporaneous with parts of these zones ; 

 for instance, the bed with Hnplites riasanensis of the government 

 of Riasan has been correlated with the zone of Virgatites virgatus, 

 and the bed with Olcostephanus hoplitoides of the same region has 

 been held to be contemporaneous with the nodiger-zonc The ex- 

 planation of these views will be found in tracing the growth of our 

 knowledge of these deposits. Prof. Rouillier established in 1845 

 the divisions of virgatus and catenulatus-beds, otherwise called the 

 Middle and Upper Moscovian stages, 1 and strictly-defined geogra- 

 phical types w T ere indicated for each of them. The further progress 

 of research in this branch of Russian geology was directed to 

 the investigation of the geographical extent of these stages and 

 to the study of their fauna. Prof. Neumayr, in his remarkable 

 work, 'Die Ornatenthone von Tchulkowo und die Stellung des 

 Russischen Jura' (1876), being without sufficient evidence to fix 

 the position of these stages in the stratigraphical series, expressed 

 the opinion that they might represent a peculiar group of beds 

 formed in the Russian basin after its separation from the West 

 European sea. These two stages were soon afterwards united under 

 the common name of the ' Volgian stage ' (from the vast Volga basin), 

 and this new title supplanted the previous names. Prom this time 

 there was a growing tendency to include in the ' Volgian stage ' all 

 the Upper Jurassic and Lower Cretaceous beds whose geological 

 age was not strictly denned, and hence it followed that various 

 horizons were from time to time considered to be contemporaneous 

 sometimes with the virgatus-be&s and sometimes with the catenulatus- 

 nodiger-beds. Under these conditions it was inevitable that there 

 should be introduced into the Volgian stage very different horizons of 

 the Jurassic and of the Cretaceous ; and after a short time this stage 

 was divided anew into two separate stages — the ' Lower Volgian,' 

 corresponding to the virgatus-heds of Rouillier, and the ' Upper 

 Volgian,' corresponding to the catenulatus-nodiger-heds of the same 

 author. The fluctuation of opinions which has taken place respecting 

 the age and extent of these stages is very natural, since the term 

 ' Volgian ' was sometimes applied to all the Upper Jurassic rocks 

 down to the base of the Kimeridgian or even of the Oxfordian ; 

 sometimes to the Upper Jurassic and the Lower Cretaceous, between 



1 Prof. Kouillier, Bull. Mosc. iv. (1845), even distinguished two ammonitic 

 zones in his Upper stage, but the characteristic ammonite of the Upper of 

 these {Ammonites nodiger), not having then received a specific name, was called 

 Ammonites, sp. 



