CHAP. IX MILD ARCTIC CLIMATES 195 



of all these lands with the possible influx of warm Avater 

 from the Pacific ; and the considerable elevation of some 

 of the Miocene beds in Greenland and Spitzbergen renders 

 it probable that these countries were then much less 

 elevated, in which case only their higher summits would 

 be covered with perpetual snow, and no glaciers would 

 descend to the sea. 



In the Pacific there was probably an elevation of land 

 counterbalancing, to some extent, the great depression of 

 so much of the northern continents. Our map in Chapter 

 XV. shows the islands that would be produced by an eleva- 

 tion of the great shoals under a thousand fathoms deep, 

 and it is seen that these all trend in a south-east and north- 

 west direction, and would thus facilitate the jjroduction of 

 definite currents impelled by the south-east trades towards 

 the north-west Pacific, where they would gain access to the 

 polar seas through Behring's Straits, which were, perhaps, 

 sometimes both wider and deeper than at present. 



Effect of these Chariges on the Climate of the Arctic Regions. 

 — These various changes of sea and land, all tending to- 

 wards a transference of heat from the equator to the north 

 temperate zone, were not improbably still further augmented 

 by the existence of a great inland South American sea 

 occupying what are now the extensive valleys of the 

 Amazon and Orinoco, and forming an additional reservoir 

 of super-heated water to add to the supply poured into the 

 North Atlantic. 



It is not of course supposed that all the modifications 

 here indicated co-existed at the same time. We have good 

 reason to believe, from the known distribution of animals 

 in the Tertiary period, that land-communications have at 

 times existed between Europe or Asia and North America, 

 either by way of Behring's Straits, or by Iceland, Green- 

 land, and Labrador. But the same evidence shows that 

 these land-communications were the exception rather than 

 the rule, and that they occurred only at long intervals and 

 for short periods, so as at no time to bring about anything 

 like a complete interchange of the productions of the two 

 continents.^ We may therefore admit that the communi- 



^ For an account of the resemblances and differences of the mammalia 



o 2 



