CHAP. IX.] 



MILD ARCTIC CLIMATES. 



187 



the constant vis a tergo, which is so efficient in the Atlantic, 

 would keep up a steady and powerful current towards the 

 northern parts of the Indian Ocean, and thence through the 

 midst of the European archipelago to the northern seas. 



Now it is quite certain that such a condition as we have 

 here sketched out would produce a wonderful effect on the 

 climate of Central Europe and Western and Northern Asia. 

 Owing to the warm currents being concentrated in inland 

 seas, instead of being dispersed over a wide ocean like the 

 North Atlantic, much more heat would be conveyed into the 

 Arctic Ocean, and this would altogether prevent the formation 

 of ice on the northern shores of Asia, which continent did not 

 then extend nearly so far north and was probably deeply inter- 

 penetrated by the sea. This open ocean to the north, and the 

 warm currents along all the northern lands, would so equalise 

 temperature, that even the northern parts of Europe might 

 then have enjoyed a climate fully equal to that of the warmer 

 parts of New Zealand at the present day, and might have well 

 supported the luxuriant vegetation of the Miocene period, even 

 without any help from similar changes in the western hemi- 

 sphere.^ 



Condition of North Americcc during the Tertiary Period. — But 

 changes of a somewhat similar character have also taken place 

 in America and the Pacific. An enormous area west of the 



^ In his recently published Lectures on Physical Geography , Professor 

 Haughton calculates, that more than half the solar heat of the torrid zone 

 is carried to the temperate zones by ocean currents. The Gulf Stream itself 

 carries one-twelfth of the total amount, but it is probable that a very small 

 fraction of this quantity of heat reaches the polar seas owing to the wide 

 area over which the current spreads in the North Atlantic. The corres- 

 ponding stream of the Indian Ocean in Miocene times would have been 

 fully equal to the Gulf Stream in heating power, while, owing to its being 

 so much more concentrated, a large proportion of its heat may have 

 reached the polar area. But the Arctic Ocean occupies less than one-tenth 

 of the area of the tropical seas ; so that, whatever proportion of the heat 

 of the tropical zone was conveyed to it, would, by being concentrated into 

 one-tenth of the surface, produce an enormously increased eif ect. Taking 

 this into consideration, we can hardly doubt that the opening of a suffi- 

 cient passage from the Indian Ocean to the Arctic seas would produce the 

 effects above indicated. 



