272 Dr. J. Croll on the Cause of 



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 

 ocean, with only a number of small steep islands to obstruct the 

 free interchange of water between the North Pole and temperate 

 or tropical regions. That the Arctic sea would, in such circum- 

 stances, be free from ice quite up to the north pole may be, I think, 

 securely inferred from what, in the present condition of the globe, 

 we know of ice-bound and open seas in the northern hemisphere 

 and of the southern ocean abounding in icebergs, but probably 

 nowhere ice-bound up to the very coast of the circumpolar Ant- 

 arctic continent, except in more or less land-locked bays 



" Suppose now the sea, unobstructed by land from either pole to 

 temperate or tropical regions, to be iceless at any time, would it 

 continue iceless during the whole of the sunless polar winter ? 

 Yes, we may safely answer. Supposing the depth of the sea to be 

 not less than 50 or 100 fathoms, and judging from what we know 

 for certain of ocean-currents, we may safely say that differences of 

 specific gravity of the water produced by difference of temperature 

 not reaching anywhere down to the freezing-point would cause 

 enough of circulation of water between the polar and temperate or 

 tropical regions to supply all the heat radiated from the water 

 within the Arctic circle during the sunless winter, if air contri- 

 buted none of it. Just think of a current of three quarters of a 

 nautical mile per hour, or 70 miles per four days, flowing towards 

 the pole across the Arctic circle. The area of the Arctic circle is 

 700 square miles for each mile of its circumference. Hence 40 

 fathoms deep of such a current would carry in, per twenty-four 

 hours, a little more than water enough to cover the whole area to 

 a depth of 1 fathom; and this, if 7°'l Cent, above the freezing- 

 point, would bring in just enough of heat to prevent freezing, if in 

 twenty-four hours as much heat w T ere radiated away as taken from 

 a tenth of a fathom of ice-cold water would leave it ice at the 

 freezing-point. This is no doubt much more than the actual 

 amount of radiation, and the supposed current is probably much 

 less than it would be if the water were ice-cold at the pole and 

 7° Cent, at the Arctic circle. Hence, without any assistance from, 

 air, we find in the convection of heat by water alone a sufficiently 

 powerful influence to prevent any freezing-up in polar regions at 

 any time of year." (Trans, of the Geol. Soc. of Glasgow, 22nd 

 February, 1877.) 



That an amount of warm water flowing into the Arctic 

 Ocean equal to that assumed by Sir William Thomson, along 

 with the effects of clouds, wind, dew, and other agencies to 

 which he refers, would wholly prevent the existence of per- 



