The land from the
southward of Chiloe to near Concepcion (lat.
37 degs.) is hidden
by one dense forest dripping with moisture. The sky is
cloudy, and we have seen how badly the fruits of southern
Europe succeed. In central Chile, on the other hand, a little
northward of Concepcion, the sky is generally clear, rain does
not fall for the seven summer months, and southern European
fruits succeed admirably; and even the sugar-cane has
been cultivated. [12] No doubt the plane of perpetual snow
undergoes the above remarkable flexure of 9000 feet,
unparalleled in other parts of the world, not far from the
latitude of Concepcion, where the land ceases to be covered
with forest-trees; for trees in South America indicate a rainy
climate, and rain a clouded sky and little heat in summer.
The descent of glaciers to the sea must, I conceive, mainly
depend (subject, of course, to a proper supply of snow in the
upper region) on the lowness of the line of perpetual snow
on steep mountains near the coast. As the snow-line is so
low in Tierra del Fuego, we might have expected that many
of the glaciers would have reached the sea. Nevertheless,
I was astonished when I first saw a range, only from 3000 to
4000 feet in height, in the latitude of Cumberland, with every
valley filled with streams of ice descending to the sea-coast.
Almost every arm of the sea, which penetrates to the interior
higher chain, not only in Tierra del Fuego, but on the coast
for 650 miles northwards, is terminated by "tremendous and
astonishing glaciers," as described by one of the officers on
the survey. Great masses of ice frequently fall from these
icy cliffs, and the crash reverberates like the broadside of a
man-of-war through the lonely channels. These falls, as
noticed in the last chapter, produce great waves which break
on the adjoining coasts. It is known that earthquakes frequently
cause masses of earth to fall from sea-cliffs: how
terrific, then, would be the effect of a severe shock (and such
occur here [13]) on a body like a glacier, already in motion, and
traversed by fissures! I can readily believe that the water
would be fairly beaten back out of the deepest channel, and
then, returning with an overwhelming force, would whirl
about huge masses of rock like so much chaff. In Eyre's
Sound, in the latitude of Paris, there are immense glaciers,
and yet the loftiest neighbouring mountain is only 6200 feet
high. In this Sound, about fifty icebergs were seen at one
time floating outwards, and one of them must have been at
least 168 feet in total height. Some of the icebergs were
loaded with blocks of no inconsiderable size, of granite and
other rocks, different from the clay-slate of the surrounding
mountains. The glacier furthest from the pole, surveyed
during the voyages of the Adventure and Beagle, is in lat.
46 degs. 50', in the Gulf of Penas. It is 15 miles long, and in
one part 7 broad and descends to the sea-coast. But even a
few miles northward of this glacier, in Laguna de San
[picture]
Rafael, some Spanish missionaries [14] encountered "many
icebergs, some great, some small, and others middle-sized," in
a narrow arm of the sea, on the 22nd of the month corresponding
with our June, and in a latitude corresponding with
that of the Lake of Geneva!
In Europe, the most southern glacier which comes down
to the sea is met with, according to Von Buch, on the coast
of Norway, in lat. 67 degs. Now, this is more than 20 degs. of
latitude, or 1230 miles, nearer the pole than the Laguna de San
Rafael. The position of the glaciers at this place and in the
Gulf of Penas may be put even in a more striking point of
view, for they descend to the sea-coast within 7.5 degs. of
latitude, or 450 miles, of a harbour, where three species of
Oliva, a Voluta, and a Terebra, are the commonest shells,
within less than 9 degs. from where palms grow, within 4.5 degs.
of a region where the jaguar and puma range over the
plains, less than 2.5 degs. from arborescent grasses, and
(looking to the westward in the same hemisphere) less than
2 degs. from orchideous parasites, and within a single degree
of tree-ferns!
These facts are of high geological interest with respect to
the climate of the northern hemisphere at the period when
boulders were transported. I will not here detail how simply
the theory of icebergs being charged with fragments of rock,
explain the origin and position of the gigantic boulders of
eastern Tierra del Fuego, on the high plain of Santa Cruz,
and on the island of Chiloe. In Tierra del Fuego, the greater
number of boulders lie on the lines of old sea-channels, now
converted into dry valleys by the elevation of the land. They
are associated with a great unstratified formation of mud
and sand, containing rounded and angular fragments of all
sizes, which has originated [15] in the repeated ploughing up of
the sea-bottom by the stranding of icebergs, and by the matter
transported on them. Few geologists now doubt that
those erratic boulders which lie near lofty mountains have
been pushed forward by the glaciers themselves, and that
those distant from mountains, and embedded in subaqueous
deposits, have been conveyed thither either on icebergs or
frozen in coast-ice. The connection between the transportal
of boulders and the presence of ice in some form, is strikingly
shown by their geographical distribution over the earth.
In South America they are not found further than 48 degs. of
latitude, measured from the southern pole; in North America
it appears that the limit of their transportal extends to
53.5 degs. from the northern pole; but in Europe to not more
than 40 degs.
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