156 
ISLAND LIFE. 
[part I. 
sea and land which occurred about the time of the glacial epoch 
may be due to an alteration of the sea-level caused by a shifting 
of the earths centre of gravity ; and physicists have generally 
admitted that the cause is a real one, and must have produced 
some effect of the kind indicated. It is evident that if ice- 
sheets several miles in thickness were removed from one polar 
area and placed on the other, the centre of gravity of the earth 
would shift towards the heavier pole, and the sea would 
necessarily follow it, and would rise accordingly. Extreme 
glacialists have maintained that during the height of the glacial 
epoch, an ice-cap extended from about 50° N. Lat. in Europe, 
and 40° N. Lat. in America, continually increasing in thickness, 
till it reached at least six miles thick at the pole ; but this view 
is now generally given up. A similar ice-cap is however be- 
lieved to exist on the Antarctic pole at the present day, and its 
transference to the northern hemisphere would, it is calculated, 
produce a rise of the ocean to the extent of 800 or 1,000 feet. 
We have, however, shown that the production of any such 
ice-cap is improbable if not impossible, because snow and ice 
can only accumulate where precipitation is greater than melting 
and evaporation, and this is never the case except in areas 
exposed to the full influence of the vapour-bearing winds. The 
outer rim of the ice-sheet w r ould inevitably exhaust the air 
of so much of its moisture that what reached the inner parts 
would produce far less snow than would be melted by the long 
hot days of summer. The accumulations of ice were therefore 
probably confined, in the northern hemisphere, to the coasts 
exposed to moist winds, and where elevated land and mountain 
ranges afforded condensers to initiate the process of glaciation, 
and we have already seen that the evidence strongly supports 
this view. Even with this limitation, how T ever, the mass of 
accumulated ice would be enormous, as indeed we have positive 
evidence that it was, and might have caused a sufficient shifting 
of the centre of gravity of the earth to produce a submergence 
of about 150 or 200 feet. 
But this would only be the case if the accumulation of ice 
on one pole was accompanied by a diminution on the other, and 
this may have occurred to a limited extent during the earlier 
