CAUSE OF MILD POLAR CLIMATES. 153 



into a series of islands allowing of the free passage of 

 water round them. But the evidence of Geology, as 

 was shown on a former occasion, * is not altogether 

 favourable to the idea that those warm climates were 

 in any way the result of a submergence of the polar 

 land. Take the Miocene epoch as an example : all the 

 way from Ireland and the Western Isles, by the Faroes, 

 Iceland, Franz-Joseph Land, to North Greenland, the 

 Miocene vegetation and the denuded fragmentary state 

 of the strata point to a much wider distribution of 

 Polar land than that which now obtains in those 

 regions. 



Mr. Alfred R. Wallace on Mild Arctic Climates. — 

 The theory that the mild climates of Arctic regions 

 were due to an inflow of warm water from intertropical 

 and temperate regions has also been fully adopted by 

 Mr. Alfred R. Wallace. But, unlike Sir William 

 Thomson, he does not attribute this transference of 

 warm water to a circulation resulting from difference 

 of density produced by difference of temperature, but 

 to currents caused by the impelling force of the wind. 



Mr. Wallace shares in the opinion, now entertained 

 by a vast number of geologists, that during the whole 

 of the Tertiary period the climate of the north tem- 

 perate and polar regions was uniformly warm and mild, 

 without a trace of any intervening epochs of cold. 

 According to him, there were no glacial or interglacial 

 periods during Tertiary times. In this case he, of 

 course, does not suppose that the inflow of warm 

 water into Arctic regions, on which the mild condition 

 of climate depended, was in any way due to those 

 physical agencies which came into operation during 

 an interglacial period. Mr. Wallace accounts for the 

 mild Arctic climate during the Tertiary period by the 



* "Geol. Mag.," September, 1878. 



