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Show 1R2 ISLAND LIFE. [PART J. repeatetl alternation of warm and glacial climates betwee~ t~e present time and the earli·e st geo 1o gi·C a1 ages. "1 And. a.g ain ' In his Slcetch of the Geology of Spitzbergen, after descnbmg the various fori.nations down to the Miocene, he s~ys : " All the fossils found in the foregoing strata show that Spit~bergen, d~ring former geological ages, enjoyed a magnific~nt chmat?, whiCh indeed was somewhat colder during the Mwcene penod, ~ut was still favourable for an extraordinarily abundant vegetatw~, muc h more 1u xun·a nt than that which now o.c curs even m t h e sou the rn part of Scandinavia·, and I have .m these stratrL soug ht I· n vai· n 1.c 0r any siOo 'n , that' as some geologists h. ave . of late endeavoured to render probable, these favourable cl~matic co.n-ditions have been broken off by intervals of .anCient gla~ml · d TI1peno s. e profiles I have had the . o. pportumty to ex.a mm.e during my various Spitzbergen expeditiOns would certu.mly,. 1f laid down on a line, occupy an extent of a thousand Engltsh rniles; and if any former glacial period hn.d existed in this reO'ion there ouO'ht to have been some trace to be observed of er~atid blocks, ~r other formations which distinguish glacial action. But this has not been the case. In the strata, whose length I have reckoned alone, I have not found a single fragment of a foreign rock so large as a child's head."2 Now it is quite impossible to ignore or evade the force of this testimony as to the continuous warm climates of the north temperate and polar zones throughout Tertiary times. The evidence extends over a vast area, both in space and time, it is derived from the work of the most competent living geologists, and it is absolutely consistent in its general tendency. We have in the Lower Cretaceous period an almost tropical climate in France and England, a somewhat lower temperature in the United States, and a mild insular clima.te in the Arctic regions. In each successive period the climate becomes somewhat less tropical; but down to the Upper Miocene it remains warm temperate in Central Europe, and cold temperate within the polar area, with not a trace of any intervening periods of Arctic cold. It then gradually cools down and merges through 1 Geological ~Magazine, 187 5, p. 531. 2 Geological L'\-[aga:~iue, 1876, p. 2G6. 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 gi vc a satisfactory explanation of its causes. The Causes of mild Ar-ctic Olimates.-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 Rance (in the geological appendix to Capt. Sir G. Nares' Na1·rative 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 period!:! are not due to any general refrigeration, but to causes which were subject to change and alternation in former age~ as now. |