310 ANTARCTICA: A VANISHED AUSTRAL LAND. 



or an archipelago extending fortlier westward," on which the progeni- 

 tors of their once existing, or still surviving, endemic flora became 

 developed. 



On a former page it was predicated that if such an austral continent 

 ever did exist, it must have been blessed with a very genial if not a 

 tropical climate, cai)able of supporting extensive forests and other lux- 

 uriant vegetation lit to harbor and nourish the marsupials, the birds, 

 and the insects found in these southern regions. That such extensive 

 forests did exist in far southern latitudes requires no more ])roof than 

 the occurrence of the fossil tree stems in Kerguelen Land and in the 

 Crozets; while I shall now try to show that the genial climate of which 

 I have spoken once prevailed in these islands. 



It is to the late Dr. James Croll that we owe the first satisfactory 

 account of the astronomical and physical causes on which climate 

 depends, especially in reference to the causes of the glacial epochs, 

 which he proved to be, in that hemisphere, due to the occurrence of 

 winter when its pole was turned away from the sun at the same time 

 that the earth during its greatest eccentricity was at its farthest dis- 

 tance in its orbit from the source of heat. Sir liobert Ball, who has 

 made some important additions to this theory (by establishing mathe- 

 matically the dilferent percentages of heat that are received in the 

 summer and in the winter of each hemisphere) emphatically asserts, as 

 a mathematician, that it is of the essence of the astronomical theory 

 that "the glaciation over the hemisphere shall be simultaneous,"' and if 

 it were not so "it would seem wholly imi)ossible to offer an explanation 

 of the phenomena by any i)hysical cause known to us." On the other 

 hand, "viewing the two hemispheres each as a whole it is imijortantto 

 observe that their respective glaciatious were not simultaneous," 

 indeed "if it could be shown that the ice ages in the two hemispheres 

 were concurrent, the astronomical doctrine would have to be forthwith 

 abandoned." " It is also of the essence of the astronomical theory," he 

 maintains, "that a glacial epoch in one hemisphere shall be accom- 

 panied by a genial epoch in the other, and that, after certain thousands 

 of years, the climatic conditions of the two hemispheres shall become 

 interchanged; that the ice shall leave - - - and the regions tbat it 

 has abandoned shall become clothed with luxuriant vegetation." Since 

 the duration of the eccentricity of the earth's orbit, when once it 

 supervenes, endures through a period in which the rotation of the line 

 of the equinoxes round the eclipse may take place more than once, 

 "clusters of ice ages and genial ages" may have followed each other 

 before each period of high eccentricity which originated them passed 

 away. "Each hemisphere is plunged alternately into extremely gla- 

 cial and extremely genial conditions, and though, no doubt, during tlie 

 transition, there may be centuries during which intermediate condi- 

 tions will prevail, yet such periods can hardly be said to have resem- 



