304 Submergence and Emergence in the Glacial Epoch. 



sink at the south pole and rise to the same extent at the north 

 in any opening or channel in the ice allowing the water to enter. 



Let the ice-cap be now transferred over to the southern hemi- 

 sphere, and the condition of things on the two hemispheres will 

 in every particular be reversed. The centre of gravity will then 

 lie to the south of c } or about 1000 feet from its former posi- 

 tion. Consequently the transference of the cap from the one 

 hemisphere to the other will produce a total submergence of 

 about 1000 feet. 



It is, of course, absurd to suppose that an ice-cap could ever 

 actually reach down to the equator. It is probable that the 

 great ice-cap of the glacial epoch nowhere reached even halfway 

 to the equator. Our cap must therefore terminate at a mode- 

 rately high latitude. Let it terminate somewhere about the 

 latitude of the north of England, say at latitude 55°. All that 

 we have to do now is simply to imagine our cap, up to that 

 latitude, becoming converted into the fluid state. This would 

 reduce the cap to less than one-half its former mass. But it 

 would not diminish the submergence to anything like that ex- 

 tent. For although the cap would be reduced to less than one- 

 half its former mass, yet its influence in displacing the centre of 

 gravity would not be diminished to that extent. This is evi- 

 dent ; for the cap now extending down to only latitude 55°, has 

 its centre of gravity much further removed from the earth's 

 centre of gravity than it had when it extended down to the 

 equator. Consequently it now possesses, in proportion to its 

 mass, a much greater power in displacing the earth's centre of 

 gravity. 



There is another fact, referred to above, which must be taken 

 into account. The common centre of gravity of the earth and 

 cap is not exactly the point around which the ocean tends to 

 adjust itself. It adjusts itself not in relation to the centre of 

 gravity of the solid mass alone, but in relation to the common 

 centre of gravity of the entire mass, solid and liquid. Now the 

 water which is pulled over from the one hemisphere to the other 

 by the attraction of the cap will also aid in displacing the centre 

 of gravity. It will cooperate with the cap and carry the true 

 centre of gravity to a point beyond that of the centre of gravity 

 of the earth and cap, and thus increase the effect. 



In the ' Reader ' for January 13, 1866, I advanced an objec- 

 tion to the submergence theory on the grounds that the lower- 

 ing of the ocean-level by the evaporation of the water to form 

 the ice-cap, would exceed the submergence resulting from the 

 displacement of the earth's centre of gravity. But, after my 

 letter had gone to press, I found that I had overlooked some 

 important considerations which seem to prove that the objection 



