J. Croll— Cause of Mild Polar Climates. 23 
remove the ice of Greenland. Any physical changes, such as 
those that have been discussed on former occasions, which 
e 
would, there is little doubt, confer on the polar regions a cli- 
mate suitable for plant and animal life. At present the Gulf- 
stream bifurcates in mid-Atlantic, one branch passing north- 
eastward into the Arctic regions, whilst the larger branch 
turns southeastward by the Azores, and after passing the 
Canaries re-enters the equatorial current. As the Gulf-stream, 
like other great currents of the ocean, follows almost exactly 
the path of the prevailing winds,* it bifurcates in mid-Atlantic 
simply because the winds blowing over it bifureate also. Any 
physical change which would prevent this bifurcation of the 
winds and cause them to blow northeastward would probably 
impel the whole of the Gulf-stream waters into the Arctic seas. 
These considerations regarding the influence of the Gulf- 
stream point to another result of an opposite character. It is 
4surope, it is obvious, as has been shown at length on former 
Orcasions, that a large decrease in its temperature and volume 
would, on the other hand, lead to a state of things in North- 
Western Kurope approaching to that which now prevails in 
Greenland. A decrease leads to a glacial, an increase to an 
Mter-glacial condition of things. 
Sir William Thomson on Mild Arctic Climates.—In a paper 
read before the Geological Society of Glasgow in February, 
1877, Sir William maintains also that an increase in the amount 
of heat conveyed by ocean-currents to the Arctic regions, com- 
bined with the effect of Clouds, Wind, and Aqueous Vapor, 
'S perfectly sufficient to account for the warm and temperate 
Condition of climate which is known to have prevailed in those 
regions during former epochs. The following quotations will 
Show Sir William’s views :— 
“A thousand feet of depression would submerge the continents 
of Europe, Asia and America, for thousands of miles from their 
present northern coast-lines, and would give instead of the present 
land-locked, and therefore ice-bound Arctic sea, an open iceless 
* See ‘ Climate and Time,’ p. 213. 
