186 Frocccdings of the Boyal Fhysical Society. 



the globe. A notable break in the succession occurs between 

 the Cretaceous and the Eocene, hardly one species of higher 

 grade than the protozoa passing from one system to the other. 

 In the Cainozoic deposits, we are no longer confronted with 

 numerous cosmopolitan species — the range of marine forms 

 has become much more restricted. Nevertheless, the faunas 

 and floras continue to be indicative of much warmer climates 

 for Arctic and temperate latitudes than now obtain. But, at 

 the same time, differentiation of climate into zones is distinctly 

 marked. In the early Cainozoic period, our present temperate 

 latitudes supported a flora of decidedly tropical affinities, 

 while the fauna of the adjacent seas had a similar character. 

 Later on the climate of the same latitudes appears to have 

 passed successively through sub-tropical and temperate stages. 

 In short, a gradual lowering of the temperature is evinced by 

 the character and distribution both of floras and faunas. 

 The differentiation of the climate during one stage of the 

 Cainozoic era is well illustrated by the Miocene flora. Thus, 

 at a time when Italy was clothed with a tropical vegetation, 

 in which palm-trees predominated, Middle Europe had its 

 extensive forests of evergreens and conifers, while in the 

 redon of the Baltic, conifers and deciduous trees were the 

 prevalent forms. 



When one takes into consideration the fact that, notwith- 

 standing many oscillations of level, the land during Cainozoic 

 times was gradually extending, and the sea disappearing 

 from wide regions which it had formerly covered, one can 

 hardly doubt that the seemingly gradual change from tropical 

 to temperate conditions was due, in large measure, to that 

 persistent continental growth. I confess, however, that it is 

 difficult to account for the very genial climate which continued 

 to prevail over the Arctic regions. So far as one can gather 

 from the evidence at present available, some of the marine 

 approaches to those latitudes had been cut off by the move- 

 ments of elevation which brought the Cainozoic era to a 

 close, while the Arctic lands were perhaps more extensive 

 than they are now. The Cretaceous Mediterranean of North 

 America had vanished, and we cannot prove that the 

 Tertiary Sea of Southern Europe communicated across the 



