244 DEVELOPMENT OF FAMILIES, ETC., IN TIME. 



" Forbes found the chalk deposits similar to those at the 

 bottom of the JEgean Sea. Recentl}^ Wyville Thompson has 

 developed this hypothesis, after the study of the bottom of the 

 Atlantic, and he believes the cretaceous period to have continued 

 to the present time in the abyssal zone ; where are living genera 

 of echinoderms, sponges and crustaceans, similar to those of the 

 white chalk. Unfortunately the conchological fauna only fur- 

 nishes negative arguments ; the relations of these mollusks being 

 onl}^ with those of the pliocene and post-pliocene beds. 



" The eocene fossils of the basin of Paris belong to genera now 

 confined to tropical seas : Rostellaria, Oliva, Ancillaria, Voluta, 

 Mitra, Pyrula, Xenophora, Typhis, Pseudoliva, Fusus, Vulsella, 

 Crassatella, Cardilia, Corbis, Pholadomya, Perna, Nautilus, 

 etc. The terrestrial genera of this basin : Cyclophorus, C^'^clotus, 

 Megaspira, Cylindrella, are now distributed through the inter- 

 tropical regions of America. The eocene fauna of Europe thus 

 has a more tropical character than its living fauna. 



" The miocene genera of the basins of Bordeaux, Touraine, 

 and Vienna are to-da}'^ distributed in the Indian Ocean, West 

 Coast of Africa and Antilles : Ancillaria, Oliva, Eburna, Terebra, 

 Cjdlene, Stronibus, Rostellaria, Ficula, Melongena, Fasciolaria, 

 Turbinella, Sigaretus, Tugonia, Perna, Ungulina, etc. 



" During the pliocene the Astrea polyps disappeared from the 

 Mediterranean, the waters became colder, the great Pleurotomas 

 became extinct, and the fauna took the characters of that which 

 is now existing. A considerable cooling permitted the glacial 

 species which existed in the Crag to penetrate to the Mediter- 

 ranean. 



" Finally, the quaternary period is that, for which great oscil- 

 lations of the earth, cataclysms, displacements of currents, are 

 invoked to explain certain geological and palseontological facts. 

 The axis of rotation of the earth itself has been displaced by 

 certain theorists. The explanation of these hypotheses would 

 take us too long. Suffice it to say that in our quaternary beds 

 are found Alpine terrestrial shells mixed with those now living 

 upon the plains, and with exotic types (Corbicula) ; just as they 

 contain mammoths, reindeer, hippopotami and lions — an assem- 

 blage which now appears to us paradoxical. This last period, so 

 close to us is thus the most obscure. It renders palpable the 

 inanity of our science in presence of the great geological and 

 palfeontological problems which still remain unsolved. What, 

 then, is it which has chiefly determined the character of the 

 present zoological provinces? What law, more powerful than 

 climate, more influential than soil, and food, and shelter; na}^, 

 often seemingly producing results opposed to a prioj-i proba- 

 bility, and at variance with the suitableness of conditions ? 



