190 ISLAND LIFE part i 



Accepting this as a substantially correct account of the 

 general climatic aspect of the Tertiary period in the 

 northern hemisphere, let us see whether the princijDles we 

 have already laid down will enable us to give a satisfactory 

 explanation of its causes. 



The Causes of mild Arctic Climates. — In his remarkable 

 series of papers on " Ocean Currents," the late Dr. James 

 Croll has jDroved, with a wealth of argument and illustra- 

 tion whose cogency is irresistible, that the very habitability 

 of our globe is due to the equalizing climatic effects of the 

 waters of the ocean ; and that it is to the same cause that 

 we owe, either directly or indirectly, almost all the chief 

 diversities of climate between places situated in the same 

 latitude. Owing to the peculiar distribution of land and 

 sea upon the globe, more than its fair proportion of the 

 Avarm equatorial waters is directed towards the western 

 shores of Europe, the result being that the British Isles, 

 Norway, and Sj^itzbergen, have all a milder climate than 

 any other parts of the globe in corresponding latitudes. A 

 very small portion of the Arctic regions, however, obtains 

 this benefit, and it thus remains, generally sj^eaking, a land 

 of snow and ice, with too short a summer to nourish more 

 than a very scanty and fugitive vegetation. The only 

 other oj)ening than that between Iceland and Britain by 

 which warm water penetrates within the Arctic circle, is 

 through Behring's Straits ; but this is both shallow and 

 limited in width, and the consequence is that the larger 

 part of the warm currents of the Pacific turns back along 

 the shores of the Aleutian Islands and North-west 

 America, while a very small quantity enters the icy 

 ocean. 



But if there were other and wider openings into the 

 Arctic Ocean, a vast quantity of tlie heated water which is 

 now turned backward would enter it, and would produce an 

 amelioration of the climate of which we can hardly form a 

 conception. A great amelioration of climate would also 

 be caused by the breaking up or the lowering of such 



climates of former periods are not due to any general refrigeration, but 

 to causes which were subject to change and alternation in former ages 



