“26 J. Croll—Cause of Mild Polar Climates. 
from difference of appeatie gravity. If there is any motion of 
the water from that cause, it must, in so far as the Atlantic is 
-concerned, be in the oes Ppponite direction, viz: from the tem- 
perate to the equatorial regio 
All, or almost all, the Yeu ‘which the Arctic seas receive 
from jntertropical regions in the form of warm water comes 
from the Atlantic, bay not from the Pacific ; for the amount of 
warm water entering by Behring Strait must be comparatively 
small. It ares follows from the foregoing considerations 
that none of that equatorial heat can be conveyed by a circula- 
tion resulting from difference of specific gravity produced by 
difference of temperature. 
It is assumed as a condition in this theory that a sabmer- 
-gence of the Arctic land of several hundred feet must have 
taken place in order to convert that land 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 favorable 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 Ire- 
land and the Western Isles, by the Faroes, Iceland, Franz-Jo- 
- Land, to North Greenland, the Miocene vegetation and 
the denuded fra gmentary state of the strata point to a much 
wider distribution of Polar land than that which now obtains 
‘in those region 
Mr. Alfr. ed R. ‘Wallace on mild Arctic Climates.—The theory 
that the mild climates of Arctic regions were due to an inflow 
-of warm water from eked vite and temperate regions has 
-also been fully adopted by Mr. Alfred R. Wallace. Bat, unlike 
‘Sir William Thomson, he fear not attribute this transference 
-of warm water to a circulation resulting from difference of 
-density produced by difference of ge? aaa but to currents 
-caused by the impelling force of the : 
Mr. Wallace shares in the opinion now entertained by a vast 
‘number of paisley 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 intervening 
-epochs of cold. According to him there were no glacial or inter- 
glacial periods during Tertiary times. a case he, of course, 
does not suppose that the inflow of w water into Arctic 
regions, on which the mild condition ny iollinate depended, was 
in any way due to those physical agencies which came into ope- 
ration during an interglacial period. Mr. Wallace accounts for 
the mild Arctic climate during the Tertiary period by the sup- 
position that at that time there were probably several channels 
oe from equatorial to arctic regions through the eastern 
: * Geol, Mag., September, 1878. 
