THE CETACEA, OR WHALES. 257 



which existed in the Miocene, and probably lasted 

 beyond that period ; when largest it extended to 

 the Arctic ocean, and also communicated with the 

 tropical seas in the south. An ocean of this kind 

 would not only confer a higher temperature upon 

 the central zones, but would also essentially con- 

 tribute to the warmth of the northern regions, 

 and further, would not merely favourably affect the 

 flora, but likewise give the fauna a very different 

 character to what it shows nowadays. This con- 

 dition was, however, by no means a permanent 

 one. The gradual rising of the land led to a 

 separation of the southern, sub-tropic or tropic 

 seas, and to a lessening of the extent of the great 

 ocean itself, and its temperature would likewise 

 decrease. This was still more the case, however, 

 with the great connecting sea in the north, more 

 particularly when its separation, and gradual dis- 

 appearance, resulted in its becoming more or 

 less detached basins. The former luxuriant and 

 fuller vegetation and animal life on the continent, 

 which had been favoured by a warmer and moister 

 climate, changed their character and became less 

 exuberant. Less organic matter being produced 

 on the land, less was carried to the ocean, where 

 it served numerous small marine animals as iood, 



