CHAP. IX.] 
MILD ARCTIC CLIMATES. 
183 
the Pliocene into the glacial epoch in Europe, while in the 
Arctic zone there is a break in the record between the Miocene 
and the recent glacial deposits . 1 
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 principles 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,” Dr. James Croll has 
proved, with a wealth of argument and illustration whose 
cogency is irresistible, that the very habitability of our globe 
is due to the equalising 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 warm equatorial waters is directed 
towards the western shores of Europe, the result being that the 
British Isles, Norway, and Spitzbergen, 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 speaking, a land 
of snow and ice, with too short a summer to nourish more than 
a very scanty and fugitive vegetation. The only other opening 
than that between Iceland and Britain by which warm water 
1 It is interesting to observe that the Cretaceous flora of the United 
States (that of the Dakota group), indicates a somewhat cooler climate 
than that of the following Eocene period. Mr. De Ranee (in the geological 
appendix to Capt. Sir Gr. Nares’ Narrative of a Voyage to the Polar Sea ) 
remarks as follows : “ In the overlying American Eocenes occur types of 
plants occurring in the European Miocenes and still living, proving the 
truth of Professor Lesquereux’s postulate, that the plant types appear in 
America a stage in advance of their advent in Europe. These plants 
point to a far higher mean temperature than those of the Dakota group, 
to a dense atmosphere of vapour, and a luxuriance of ferns and palms.” 
This is very important as adding further proof to the view that the 
climates of former periods are not due to any general refrigeration, but 
to causes which were subject to change and alternation in former ages 
as now. 
