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 . 1 
Condition of North America 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 
1 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 effect. 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. 
