604 WOODWARD, POLAR GLACIATION, ETC. 



A part of the coast of Greenland is said to be in a state of sub- 

 sidence ; but Greenland is noio undergoing intense glaciation^ and 

 is buried in snow and ice piled mountains high. All the geological 

 evidence is in favour of these lands having been above the sea in 

 Pre-glacial times. The lands' around the Poles must then have 

 sank down after they were covered with ice, and they have been 

 slowly rising since it melted away. 



Mr. Belt believes the cause of the depression was the piling up 

 of so vast a weight of ice around the Poles, and that the cause of 

 the elevation was the removal of that vast weight by the gradual 

 meltingof the ice 



That the movement of elevation still continues in some places 

 only shows that the earth is a (more or less) rigid body, and gives 

 way but slowly to great strains. 



In considering the theories which have been put forward in 

 order to account for the cold of the Glacial Epoch, one important 

 point to be borne in mind is the relative time assumed to be occu- 

 pied by the respective operations of eccentricity of the Earth's 

 orbit, on the one hand, and greater obliquity of the Ecliptic, on the 

 other. 



Thus, Mr. Croll's theory of the eccentricity of the earth's 

 orbit requires a period of 200,000 years to elapse. On the other 

 hand, Mr. Belt's theory of the greater obliquity of the Ecliptic 

 would not require much more than 20,000 years, or one-tenth of 

 the time demanded by Mr. Croll 



If our Glacial period merely necessitated, as Mr. Ckoll sup- 

 poses, the heaping up of snow and ice around the North Pole, the 

 only result would be a slight shifting of the centre of gravity of 

 the Earth northwards ; but, if it was contemporaneous in the two 

 hemispheres (as Mr. Belt assumes), the figure of the Earth would 

 be changed, its Polar diameter would be lengthened, its mean 

 Equatorial diameter shortened, and a series of strains would be set 

 up, tending to restore its figure to a state of equilibrium. And if, 

 during the Glacial Epoch, that state had been arrived at by the 

 sinking-down of the circumpolar land, and the rising of land in 

 the Tropics, then, when the ice melted away, the Polar diameter 

 would be shortened, the mean Equatorial diameter lengthened, and 

 forces would be set in operation tending to lower the land at the 

 Tropics, and raise that around the Poles. 



That the deepening of tropical seas, as evidenced by the growth 

 of Coral islands, is due to an actual sinking of the bed of the ocean 

 is perfectly in accord with this theory. But whether by the deep- 

 ening of the sea by addition to its volume, or by depression of its 

 bed, the cause (according to Mr. Belt) has been the gradual 

 melting of the ice piled up during the Glacial Epoch, which, by 

 its liberation, has disturbed the equilibrium of the figure of the 

 Earth 



