158 



ISLAND LIFF. 



[pARr 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 Flanet Mars, as hearing on the Theory of 

 Excentricity as a cause of Glacial Feriocls. — 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 (y6\. xxvii. p. 

 539), describes similar phenomena in the sam^e 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 Eio 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. 



