Evidence Derived From An Inclined Stream
Of Lava At The Eastern Base Of The Portillo, Might Be Adduced
To Show, That It Owes Part Of Its Great Height To Elevations Of
A Still Later Date.
Looking to its earliest origin, the red
granite seems to have been injected on an ancient pre-existing
line of white granite and mica-slate.
In most parts, perhaps in
all parts, of the Cordillera, it may be concluded that each line
has been formed by repeated upheavals and injections; and
that the several parallel lines are of different ages. Only
thus can we gain time, at all sufficient to explain the truly
astonishing amount of denudation, which these great, though
comparatively with most other ranges recent, mountains have
suffered.
Finally, the shells in the Peuquenes or oldest ridge, prove,
as before remarked, that it has been upraised 14,000 feet
since a Secondary period, which in Europe we are accustomed
to consider as far from ancient; but since these shells
lived in a moderately deep sea, it can be shown that the area
now occupied by the Cordillera, must have subsided several
thousand feet - in northern Chile as much as 6000 feet - so
as to have allowed that amount of submarine strata to have
been heaped on the bed on which the shells lived. The proof
is the same with that by which it was shown, that at a much
later period, since the tertiary shells of Patagonia lived,
there must have been there a subsidence of several hundred
feet, as well as an ensuing elevation. Daily it is forced home
on the mind of the geologist, that nothing, not even the wind
that blows, is so unstable as the level of the crust of this
earth.
I will make only one other geological remark: although
the Portillo chain is here higher than the Peuquenes, the
waters draining the intermediate valleys, have burst through
it. The same fact, on a grander scale, has been remarked in
the eastern and loftiest line of the Bolivian Cordillera,
through which the rivers pass: analogous facts have also
been observed in other quarters of the world. On the supposition
of the subsequent and gradual elevation of the Portillo
line, this can be understood; for a chain of islets would
at first appear, and, as these were lifted up, the tides would
be always wearing deeper and broader channels between them.
At the present day, even in the most retired Sounds on the
coast of Tierra del Fuego, the currents in the transverse
breaks which connect the longitudinal channels, are very
strong, so that in one transverse channel even a small vessel
under sail was whirled round and round.
About noon we began the tedious ascent of the Peuquenes
ridge, and then for the first time experienced some little
difficulty in our respiration. The mules would halt every fifty
yards, and after resting for a few seconds the poor willing
animals started of their own accord again. The short breathing
from the rarefied atmosphere is called by the Chilenos
"puna;" and they have most ridiculous notions concerning
its origin. Some say "all the waters here have puna;" others
that "where there is snow there is puna;" - and this no
doubt is true. The only sensation I experienced was a slight
tightness across the head and chest, like that felt on leaving
a warm room and running quickly in frosty weather. There
was some imagination even in this; for upon finding fossil
shells on the highest ridge, I entirely forgot the puna in my
delight. Certainly the exertion of walking was extremely
great, and the respiration became deep and laborious: I am
told that in Potosi (about 13,000 feet above the sea) strangers
do not become thoroughly accustomed to the atmosphere for
an entire year. The inhabitants all recommend onions for
the puna; as this vegetable has sometimes been given in
Europe for pectoral complaints, it may possibly be of real
service: - for my part I found nothing so good as the fossil
shells!
When about half-way up we met a large party with seventy
loaded mules. It was interesting to hear the wild cries
of the muleteers, and to watch the long descending string
of the animals; they appeared so diminutive, there being
nothing but the black mountains with which they could be
compared. When near the summit, the wind, as generally
happens, was impetuous and extremely cold. On each side of
the ridge, we had to pass over broad bands of perpetual
snow, which were now soon to be covered by a fresh layer.
When we reached the crest and looked backwards, a glorious
view was presented. The atmosphere resplendently clear;
the sky an intense blue; the profound valleys; the wild
broken forms: the heaps of ruins, piled up during the lapse
of ages; the bright-coloured rocks, contrasted with the quiet
mountains of snow, all these together produced a scene no
one could have imagined. Neither plant nor bird, excepting
a few condors wheeling around the higher pinnacles, distracted
my attention from the inanimate mass. I felt glad
that I was alone: it was like watching a thunderstorm, or
hearing in full orchestra a chorus of the Messiah.
On several patches of the snow I found the Protococcus
nivalis, or red snow, so well known from the accounts of
Arctic navigators. My attention was called to it, by observing
the footsteps of the mules stained a pale red, as if their
hoofs had been slightly bloody. I at first thought that it was
owing to dust blown from the surrounding mountains of red
porphyry; for from the magnifying power of the crystals
of snow, the groups of these microscopical plants appeared
like coarse particles. The snow was coloured only where it
had thawed very rapidly, or had been accidentally crushed.
A little rubbed on paper gave it a faint rose tinge mingled
with a little brick-red. I afterwards scraped some off the
paper, and found that it consisted of groups of little spheres
in colourless cases, each of the thousandth part of an inch in
diameter.
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