Mild Polar Climates. 275 



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 b} r avast 

 number of geologists, that during the whole of the Tertiary 

 period the climate of the north temperate and polar regions 

 was uniformly warm and mild, without a trace of any inter- 

 vening 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 cli- 

 mate 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 Ter- 

 tiary period by the supposition that at that time there were 

 probably several channels extending from equatorial to arctic 

 regions through the eastern and western continents, allowing 

 of a continuous flow of intertropical water into the Arctic 

 Ocean. Mr. Wallace expresses his views on the point 

 thus : — 



" The distribution of the Eocene and Miocene formations 

 shows that during a considerable portion of the Tertiary 

 period an inland sea, more or less occupied by an archipelago 

 of islands, extended across Central Europe between the Baltic 

 and the Black and Caspian Seas, and thence by narrower 

 channels south-eastward to the valley of the Euphrates and 

 the Persian Gulf, thus opening a communication between the 

 North Atlantic and the Indian Ocean. From the Caspian also 

 a wide arm of the sea extended during some part of the 

 Tertiary epoch northwards to the Arctic Ocean ; and there is 

 nothing to show that this sea may not have been in existence 

 during the whole Tertiary period. Another channel probably 

 existed over Egypt into the eastern basin of the Mediterranean 

 and the Black Sea ; while it is probable that there was a com- 

 munication between the Baltic and the White Sea, leavino- 

 Scandinavia as an extensive island. Turning to India, we find 

 that an arm of the sea of great width and depth extended from 

 the Bay of Bengal to the mouths of the Indus ; while the 

 enormous depression indicated by the presence of marine 

 fossils of Eocene age at a height of 16,500 feet in Western 

 Tibet renders it not improbable that a more direct channel 

 across Afghanistan may have opened a communication between 

 the West-Asiatic and Polar seas." - (' Island Life/ p. 184.) 



My acquaintance with the Tertiary formations of the globe, 

 and with the distribution of land and water during that period, 

 is not such as to enable me to form any opinion whatever 



