132 
ISLAND LIFE. 
[part i. 
elevated borders ; while the polar arep, 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. 1 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. 
