320 The History of our Earth. [July, 
The differences of view between Mr. Belt and Mr. Croll may 
be summed up as follows :—The former ascribes the former 
emergence of regions now under water to the general 
decrease of the amount of water present in a fluid state, 
while the latter attributes the same phenomenon to the 
accumulation of water in the glaciated hemisphere. Mr. 
Belt considers that low-lying lands might be left bare in the 
immediate vicinity of glaciated regions—e.g. territories now 
covered by the Caribbean Sea during the glaciation of 
Central America—and might serve as a refuge for tropical 
forms of organic life. Mr. Croll, on the contrary, holds 
that the sea can only recede in the non-glaciated hemi- 
sphere, and must of necessity rise in the glaciated above its 
present level. Finally, as is implied in the foregoing 
remarks, Mr. Belt assumes—if we do not misunderstand 
him—that a Glacial epoch might simultaneously invade 
both hemispheres, whilst if Mr. Croll’s hypothesis is well- 
founded, it is, of necessity, limited to one. 
Both these authors consider—and we must admit that in 
so doing they are warranted by facts—that of the evident 
alternations of land and sea noticed even by Ovid, many 
have been caused by a local increase or decrease of the 
depth of the latter. But neither of them asserts that all 
such changes are to be ascribed to this cause, or denies the 
existence of those areas of elevation and of subsidence to 
which Mr. Darwin draws attention in his ‘‘ Naturalist’s 
Voyage.” ‘The question is one which can be settled by 
careful observation. If we find that the sea gains upon the 
land simultaneously throughout the whole of one hemi- 
sphere, most markedly in high latitudes, and to a less and 
less extent as we approach the Equator, we should then be 
warranted in concluding that the encroachment was due to 
an increasing accumulation of water in that hemisphere. 
But if we observe the land in South America gradually 
rising higher and higher out of the water, whilst in certain 
of the South Sea islands it is gradually sinking, we should 
then be justified in seeking the cause in the crust of the 
earth, and in pronouncing South America an area of 
elevation and the Pacific Isles an area of subsidence. 
Incidentally we have referred to the theory of M. 
Adhémar. ‘This author seems to have been the first who 
pointed out the possible displacement of the earth’s centre 
of gravity by means of an ice-cap accumulating on either 
pole. But he supposes this cap to rest, not upon circum- 
polar land, but upon the bottom of the sea, and to attain the 
height not of 12 or 24 miles, as Mr. Croll supposes, but of 
