194 ISLAND LIFE 



North Atlantic, mucli 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 with- 

 out any help from similar changes in the western hemi- 

 sphere.^ 



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 Mississippi, extending over much of the 

 Rocky Mountains, consists of marine Cretaceous beds 

 10,000 feet thick, indicating great and long-continued sub- 

 sidence, and an insular condition of Western America with 

 a sea probably extending northwards to the Arctic Ocean. 

 As marine Tertiary deposits are found conformably over- 

 lying these Cretaceous strata. Professor Dana is of opinion 

 that the great elevation of this part of America did not 

 begin till early Tertiary times. Other Tertiary beds in 

 California, Alaska, Kamschatka, the Mackenzie River, the 

 Parry Islands, and Greenland, indicate partial submergence 



^ In his recently published Lectui^es on Physical Gcogra'pliy, 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 corre- 

 sponding stream of the Indian Ocean in ^Miocene times would have been 

 fully equal to the Gulf Stream in heating power, Avhile, 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 sufficient 

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

 above indicated. 



