On the
other hand, in the intertropical parts of America, Asia, and
Africa, they have never been observed; nor at the Cape of Good
Hope, nor in Australia.
[16]
On the Climate and Productions of the Antarctic Islands.
- Considering the rankness of the vegetation in Tierra del
Fuego, and on the coast northward of it, the condition of the
islands south and south-west of America is truly surprising.
Sandwich Land, in the latitude of the north part of Scotland,
was found by Cook, during the hottest month of the
year, "covered many fathoms thick with everlasting snow;"
and there seems to be scarcely any vegetation. Georgia, an
island 96 miles long and 10 broad, in the latitude of Yorkshire,
"in the very height of summer, is in a manner wholly
covered with frozen snow." It can boast only of moss, some
tufts of grass, and wild burnet; it has only one land-bird
(Anthus correndera), yet Iceland, which is 10 degs. nearer the
pole, has, according to Mackenzie, fifteen land-birds. The
South Shetland Islands, in the same latitude as the southern
half of Norway, possess only some lichens, moss, and a little
grass; and Lieut. Kendall [17] found the bay, in which he was
at anchor, beginning to freeze at a period corresponding with
our 8th of September. The soil here consists of ice and
volcanic ashes interstratified; and at a little depth beneath
the surface it must remain perpetually congealed, for Lieut.
Kendall found the body of a foreign sailor which had long
been buried, with the flesh and all the features perfectly
preserved. It is a singular fact, that on the two great
continents in the northern hemisphere (but not in the broken
land of Europe between them ), we have the zone of perpetually
frozen under-soil in a low latitude - namely, in 56 degs. in
North America at the depth of three feet, [18] and in 62 degs.
in Siberia at the depth of twelve to fifteen feet - as the
result of a directly opposite condition of things to those
of the southern hemisphere. On the northern continents, the
winter is rendered excessively cold by the radiation from a
large area of land into a clear sky, nor is it moderated by
the warmth-bringing currents of the sea; the short summer,
on the other hand, is hot. In the Southern Ocean the winter
is not so excessively cold, but the summer is far less hot,
for the clouded sky seldom allows the sun to warm the ocean,
itself a bad absorbent of heat: and hence the mean temperature
of the year, which regulates the zone of perpetually congealed
under-soil, is low. It is evident that a rank vegetation,
which does not so much require heat as it does protection
from intense cold, would approach much nearer to this zone
of perpetual congelation under the equable climate of the
southern hemisphere, than under the extreme climate of the
northern continents.
The case of the sailor's body perfectly preserved in the icy
soil of the South Shetland Islands (lat. 62 to 63 degs. S.), in a
rather lower latitude than that (lat. 64 degs. N.) under which
Pallas found the frozen rhinoceros in Siberia, is very
interesting. Although it is a fallacy, as I have endeavoured to
show in a former chapter, to suppose that the larger quadrupeds
require a luxuriant vegetation for their support, nevertheless
it is important to find in the South Shetland Islands
a frozen under-soil within 360 miles of the forest-clad islands
near Cape Horn, where, as far as the _bulk_ of vegetation is
concerned, any number of great quadrupeds might be supported.
The perfect preservation of the carcasses of the
Siberian elephants and rhinoceroses is certainly one of the
most wonderful facts in geology; but independently of the
imagined difficulty of supplying them with food from the
adjoining countries, the whole case is not, I think, so
perplexing as it has generally been considered. The plains of
Siberia, like those of the Pampas, appear to have been formed
under the sea, into which rivers brought down the bodies
of many animals; of the greater number of these, only the
skeletons have been preserved, but of others the perfect
carcass. Now, it is known that in the shallow sea on the Arctic
coast of America the bottom freezes, [19] and does not thaw in
spring so soon as the surface of the land, moreover at
greater depths, where the bottom of the sea does not freeze
the mud a few feet beneath the top layer might remain even
in summer below 32 degs., as in the case on the land with the
soil at the depth of a few feet. At still greater depths, the
temperature of the mud and water would probably not be low
enough to preserve the flesh; and hence, carcasses drifted
beyond the shallow parts near an Arctic coast, would have
only their skeletons preserved: now in the extreme northern
parts of Siberia bones are infinitely numerous, so that even
islets are said to be almost composed of them; [20] and those
islets lie no less than ten degrees of latitude north of the
place where Pallas found the frozen rhinoceros. On the other
hand, a carcass washed by a flood into a shallow part of the
Arctic Sea, would be preserved for an indefinite period, if it
were soon afterwards covered with mud sufficiently thick to
prevent the heat of the summer-water penetrating to it; and
if, when the sea-bottom was upraised into land, the covering
was sufficiently thick to prevent the heat of the summer air
and sun thawing and corrupting it.
Recapitulation. - I will recapitulate the principal facts with
regard to the climate, ice-action, and organic productions of
the southern hemisphere, transposing the places in imagination
to Europe, with which we are so much better acquainted.
Then, near Lisbon, the commonest sea-shells, namely, three
species of Oliva, a Voluta, and a Terebra, would have a
tropical character.
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