GEOLOGICAL CLIMATE. 287 



area would therefore diminish (for it does not 

 increase at present). The smaller the area of ice 

 round the pole, the more rapidly must its boundary 

 be eaten into by the water, and the less abundant 

 can be the replenishment from the interior towards 

 compensating for this consumption. Hence the 

 ice must all melt away in time. 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 contributed none of it. Just think of a 

 current of three quarters of a nautical mile per 



