CHAP. VIII THE CAUSES OF GLACIAL EPOCHS 137 



in thickness.^ As this is the thickness of the outer edge 

 of the ice it must be far thicker inland ; and we thus find 

 that the Antarctic continent is at this very time suffering 

 glaciation to quite as great an extent as we have reason to 

 believe occurred in the same latitudes of the northern 

 hemisphere during the last glacial epoch. 



The accompanying diagrams show the comparative state 

 of the two polar areas both as regards the distribution of 

 land and sea, and the extent of the ice-sheet and floating 

 icebergs. The much greater quantity of ice at the south 

 pole is undoubtedly due to the presence of a large extent 

 of high land, which acts as a condenser, and an unbroken 

 surrounding ocean, which affords a constant supply of 

 vapour; and the effect is intensified by winter being 

 there in aphelion, and thus several days longer than 

 with us, while the whole southern hemisphere is at 

 that time farther from the sun, and therefore receives 

 less heat. 



We see, however, that with less favourable conditions for 

 the production and accumulation of ice, Greenland is 

 glaciated down to Lat. 61°. What, then, would be the 

 effect if the Antarctic continent, instead of being confined 

 almost wholly within the south polar circle, were to extend 

 in one or two great mountainous promontories far into the 

 temperate zone ? The comparatively small Heard Island 

 in S. Lat. 53° is even now glaciated down to the sea. What 

 would be its condition were it a northerly extension of a 

 lofty Antarctic continent? We may be quite sure that 

 glaciation would then be far more severe, and that an ice- 

 sheet corresponding to that of Greenland might extend to 

 beyond the parallel of 50° S. Lat. Even this is probably 

 much too low an estimate, for on the west coast of New 

 Zealand in S. Lat. 43° 35' a glacier even now descends to 

 within 705 feet of the sea-level ; and if those islands were 

 the northern extension of an Antarctic continent, we may 

 be pretty sure that they would be nearly in the ice- 

 covered condition of Greenland, although situated in the 

 latitude of Marseilles. 



^ ''On the Glacial Epoch," by James Croll. Geol. Magi July, August, 

 1874. 



