132 



ISLAND LIFE. 



[part I. 



elevated borders ; while the polar area is, with the exception of 

 Greenland and a few other considerable islands, almost all water. 

 In the southern hemisphere the temperate zone is almost all 

 water, while the polar area is almost all land, or is at least inclosed 

 by a ring of high and mountainous land. The result is that in 

 the north the polar area is free from any accumulation of per- 

 manent ice (except on the highlands of Greenland and Grin- 

 nell's Land), while in the south a complete barrier of ice of 

 enormous thickness appears to surround the pole. Dr. Croll 

 shows, from the measured height of numerous Antarctic ice- 

 bergs (often miles in length) that the ice-sheet from which they 

 are the broken outer fragments must be from a mile to a mile 

 and a half 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 glacia- 

 tion 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 



1 " On the Glacial Epoch," by James Croll. Geol. Mag, July, August, 

 1874. 



