158 
ISLAND LIFF. 
[part I. 
would lower the whole ocean by the quantity of water abstracted 
from it, while any want of perfect synchronism between the 
decrease of the ice at the two poles would cause a movement 
of the centre of gravity of the earth, and a slight rise of the 
sea-level at one pole and depression at the other. It is also 
generally believed that a great accumulation of ice might cause 
subsidence by its pressure on the flexible crust of the earth, 
and we thus have a very complex series of agents leading to 
elevations and subsidences of limited amount, such as seem 
always to have accompanied glaciation. This complexity of 
the causes at work may explain the somewhat contradictory 
evidence as to rise and fall of land, some authors maintaining 
that it stood higher, and others lower, during the glacial 
period. 
The state of the Planet Mars, as bearing on the Theory of 
Excentricity as a cause of Glacial Periods. — It is well known 
that the polar regions of the planet Mars are covered with white 
patches or discs, which undergo considerable alterations of size 
according as they are more or less exposed to the sun’s rays. 
S. Lat. 20,000, with far more extensive plateaus, produce no ice-fields. 
"We cannot, therefore, believe that a few thousand feet of additional eleva- 
tion, even if it occurred so recently as indicated by the presence of stria- 
tions, would have produced the remarkable amount of glaciation above 
described ; while from the analogy of the northern hemisphere, we may 
well believe that it was mainly due to the same high excentricity that led to 
the glaciation of Western and Central Europe, and Eastern North America. 
These observations confirm those of Mr. G. W. Stow, who, in a paper 
published in the Quarterly Journal of the Geological Society (Vol. xxvii. p. 
539), describes similar phenomena in the same mountains, and also mounds 
and ridges of unstratified clay packed with angular boulders ; while further 
south the Stormberg mountains are said to be similarly glaciated, with im- 
mense accumulations of morainic matter in all the valleys. We have here 
all the chief surface phenomena characteristic of a glaciated country only 
a few degrees south of the tropic ; and taken in connection with the evi- 
dence of Professor Hartt, who describes true moraines near Rio de Janeiro, 
situated on the tropic itself, we can hardly doubt the occurrence of some 
general and wide-spread cause of glaciation in the southern hemisphere at 
a period so recent that the superficial phenomena are as well preserved as 
in Europe. Such evidences of recent glaciation in the southern hemi- 
sphere are quite inexplicable without calling in the aid of the recent phase of 
high excentricity ; and they may be fairly claimed as adding another link 
to the long chain of argument in favour of the theory here advocated. 
