64 PROCEEDINGS OF WASHINGTON MEETING. 



Certain groups of ammonites present no less striking examples, proving that a 

 climatic change took place in the seas of middle latitudes in the northern hemis- 

 phere at the beginning of the Cretaceous period. The characteristic cephalopoda 

 of the lower Cretaceous of middle Europe are well known. They are especially the 

 belemnites of the group Hastati, the flat belemnites, the ammonites related to the 

 group of Olcoslefanus astieri, the representatives of the genus OlcodiStus, and some 

 hoplites. 



As regards the belemnites, we know already that they are southern forms. Fix- 

 ing our attention on 0. astieri, and its kindred, it is not difficult to see that it is a 

 southern form. We know it in India and in South Africa [A. aiherstoni), and the 

 British museum contains a very good specimen from South America. In Russia 

 we know these forms in the Crimeo-Caucassian region. In northern England 

 they appeared with the Hastati, to replace the boreal fauna, and to inaugurate the 

 typical Neocomian. The same thing might be said of the representatives of the 

 genus Olcodiscus and of some hoplites characteristic of the Neocomian. Thus the 

 study of the cephalopoda of the upper Jurassic and of the Neocomian demonstrates 

 that the forms are the same in central and eastern Russia, in northern England, in 

 Germany, and, in part, in southern England and in France ; that in the last two 

 regions the fauna presents a mixed character, the boreal forms being there found 

 together with the southern, the latter becoming more and more numerous as we 

 go southward. The boundary separating the two faunas does not always remain 

 the same. Certain epochs may be pointed out when the southern fauna advanced 

 northward, driving back the boreal fauna, which afterward resumed its sway. This 

 complicates the series of the beds which we are studying as well as their history 

 and we are often embarrassed in regard to the establishment of the exact corre- 

 spondence of the beds. But, on the other hand, we recognize horizons common to 

 the two great regions of the globe, and we are in condition to establish the strict 

 correspondence of the beds and to decipher the geologic history of the whole world, 

 provided we do not neglect the systematic paleontologic studies which indicate the 

 development of the important groups of the animal kingdom, suchas the belemnites 

 and the ammonites. 



I have demonstrated that an interesting change took place in the physio-geo- 

 graphic conditions in a vast region, extending from eastern Russia to England. It 

 cannot be said that this was due to a local oscillation of sea-level. Not only is this 

 true, but the same forms of cephalopoda are found in the Jurassic and Cretaceous 

 beds of America. There, too, the two faunas, the southern and the boreal, may be 

 distinguished. The regions where these faunas meet (California, for example) pre- 

 sent difficulties to the observer, but they promise at the same time to yield a uni- 

 form and general classification for all countries, and to render intelligible and simple 

 the general history of our globe — that mysterious history which thus becomes more 

 and more attractive. 



American geologists have before them the same scientific problems that engage 

 our attention in Europe. Their solution will be speedier and easier if we work 

 together. This suggested to me the idea of setting forth before you the direction 

 and some of the results of my studies. Our science knows not the artificial bound- 

 aries that separate nations, nor will it recognize natural boundaries, such as 

 oceans. The history of our globe has for a long time been the common work of all 

 nations and of all peoples, just as the globe itself will one day be the common heri- 

 tage of humanity, one and united* 



*For further details, see Bull, de la Soc. des Naturalistes de Moscow, 1891. 



