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The features in the scenery of the Andes which struck me
most, as contrasted with the few other mountain chains with
which I am acquainted, were,—the flat fringes sometimes
expanding into narrow plains on each side the valleys,—the
bright colours, chiefly red and purple, of the utterly bare
and precipitous hills,—the grand and continuous wall-hke
dikes,—the strongly-marked strata which, when nearly vertical,
form the most picturesque and wild pinnacles, but
where less inclined, great massive mountains; the latter
occupying the outskirts of tlie range, and the former the
more lofty and central parts,—lastly, the smooth conical
piles of fine and brightly-coloured detritus, which slope at
a high angle from the flanks of the mountains to their bases,
some of the piles having a height of more than two thousand
feet.
I frequently observed both in Tierra del Fuego, and
within the Andes, that where the rock was covered during
the greater part of the year with snow, it was shivered m
a very extraordinary manner into small angular fragments.
Scoresby* has observed the same fact in Spitzbergen: he
says, “ The invariably broken state of the rocks appeared to
have' been the eftect of frost. On calcareous rocks, some
of which are not impervious to moisture, the effect is such
as might have been expected ; but how frost can operate in
this way on quartz is not so easily understood.” The whole
phenomenon appears to me rather obscure: for that part of
the mountain which is covered during many months by a
mantle of snow, must be less subject to repeated and great
changes of temperature than any other, yet it is the most
affected. I have sometimes thought, that the earth and
fragments of stone lying on the surface, were perhaps less
effectually removed by means of slowly percolating snowwater,!
than by the agency of rain, and therefore that the
• S co resb y ’s A rc tic R e g io n s , vo l. i., p . 122.
t I h a v e h e a rd i t r em a rk e d in S h ro p sh ire , t h a t th e w a te r, w h e n th e
S e v e rn is flo o d ed from lo n g -c o n tin u e d r a in , is m u c h m o re tu rb id , th a n
w h e n i t p ro c e e d s from th e sn ow m e ltin g o n th e W e ls h m o u n ta in s . T h e
appearance of a quicker decay of the solid rock may be
deceptive. Whatever the cause may be, the quantity of
crumbling stone on the Cordillera is very great. Occasionally
in the spring, masses of such matter slide down
the mountains, and cover the snow-drifts in the valleys ;
thus forming natural ice-houses. We rode over one, the
elevation of which was far below the limit of perpetual
congelation.
As the evening drew to a close, we reached the Valle del
Yeso. This is a very singular basin, which must have once
been a very deep and large lake: the barrier is formed by a
huge mountain of alluvium, on one side of which the river
has cut a gorge. The plain is covered by a little dry pasture,
and amidst the surrounding rocky deserts we had the
pleasant sight of a herd of cattle. The valley takes its name
of Yeso from a great bed, I should think at least two thousand
feet thick, of white, and in some parts quite pure,
gypsum. We slept with a party of men, who were employed
in loading mules with this substance, which is used
in the manufacture of wine.
M a r c h 2 1 s t .—We set out early in the morning, and
continued to follow the course of the river, which by this
time had become small, till we arrived at the foot of the
ridge that separates the w-aters flowing into the Pacific and
Atlantic oceans. The road, which as yet had been good,
with a steady but very gradual ascent, now changed into a
steep zigzag track. The Cordillera in this part consists of
two principal ranges; the passes across which attain respectively
an elevation of 13,210 and 14,365 feet.* The
first great line (consisting of course of many subordinate
ones) is called Peuquenes. It divides the waters, and thercfloods
a lso, in th e fo rm e r case, a re sa id to b e m o re d e s tru c tiv e to tlie
lan d . D ’O rb ig n y (v o l. i., p . 184), in e x p la in in g th e c a u se o f th e v a rio u s
c o lo u rs o f th e riv e rs in S o u th A m e ric a , rem a rk s t h a t th o s e w ith b lu e o r
c le a r w a te r, h a v e th e i r so u rc e in tlie C o rd ille ra , w h e re th e sn ow m e lts.
* M e a su rem e n ts m ad e b y D r . G illie s ; E d in b u rg h J o u rn a l o f N a t .
a n d G e o g ra p h . Sc ien c e , A u g u s t, 1830.