155 



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 earth's 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 poJar 

 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 would inevitably exhaust the air 

 of so much of its moisture that what reached the inner parts 

 would produce fardess 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, however, 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 



