These Fringes Evidently
Once Extended Across The Valleys And Were United; And The
Bottoms Of The Valleys In Northern Chile, Where There Are No
Streams, Are Thus Smoothly Filled Up.
On these fringes the
roads are generally carried, for their surfaces are even, and
they rise, with a very gentle slope up the valleys:
Hence, also,
they are easily cultivated by irrigation. They may be traced
up to a height of between 7000 and 9000 feet, where they
become hidden by the irregular piles of debris. At the lower
end or mouths of the valleys, they are continuously united to
those land-locked plains (also formed of shingle) at the foot
of the main Cordillera, which I have described in a former
chapter as characteristic of the scenery of Chile, and which
were undoubtedly deposited when the sea penetrated Chile, as
it now does the more southern coasts. No one fact in the
geology of South America, interested me more than these
terraces of rudely-stratified shingle. They precisely resemble
in composition the matter which the torrents in each valley
would deposit, if they were checked in their course by any
cause, such as entering a lake or arm of the sea; but the
torrents, instead of depositing matter, are now steadily at
work wearing away both the solid rock and these alluvial
deposits, along the whole line of every main valley and side
valley. It is impossible here to give the reasons, but I am
convinced that the shingle terraces were accumulated, during
the gradual elevation of the Cordillera, by the torrents
delivering, at successive levels, their detritus on the
beachheads of long narrow arms of the sea, first high up the
valleys, then lower and lower down as the land slowly rose. If
this be so, and I cannot doubt it, the grand and broken chain
of the Cordillera, instead of having been suddenly thrown up,
as was till lately the universal, and still is the common
opinion of geologists, has been slowly upheaved in mass, in the
same gradual manner as the coasts of the Atlantic and Pacific
have risen within the recent period. A multitude of facts in the
structure of the Cordillera, on this view receive a simple
explanation.
The rivers which flow in these valleys ought rather to be
called mountain-torrents. Their inclination is very great,
and their water the colour of mud. The roar which the
Maypu made, as it rushed over the great rounded fragments,
was like that of the sea. Amidst the din of rushing waters,
the noise from the stones, as they rattled one over another,
was most distinctly audible even from a distance. This rattling
noise, night and day, may be heard along the whole
course of the torrent. The sound spoke eloquently to the
geologist; the thousands and thousands of stones, which,
striking against each other, made the one dull uniform sound,
were all hurrying in one direction. It was like thinking on
time, where the minute that now glides past is irrevocable.
So was it with these stones; the ocean is their eternity, and
each note of that wild music told of one more step towards
their destiny.
It is not possible for the mind to comprehend, except by
a slow process, any effect which is produced by a cause repeated
so often, that the multiplier itself conveys an idea,
not more definite than the savage implies when he points to
the hairs of his head. As often as I have seen beds of mud,
sand, and shingle, accumulated to the thickness of many
thousand feet, I have felt inclined to exclaim that causes,
such as the present rivers and the present beaches, could
never have ground down and produced such masses. But, on
the other hand, when listening to the rattling noise of these
torrents, and calling to mind that whole races of animals have
passed away from the face of the earth, and that during this
whole period, night and day, these stones have gone rattling
onwards in their course, I have thought to myself, can any
mountains, any continent, withstand such waste?
In this part of the valley, the mountains on each side were
from 3000 to 6000 or 8000 feet high, with rounded outlines
and steep bare flanks. The general colour of the rock was
dullish purple, and the stratification very distinct. If the
scenery was not beautiful, it was remarkable and grand. We
met during the day several herds of cattle, which men were
driving down from the higher valleys in the Cordillera. This
sign of the approaching winter hurried our steps, more than
was convenient for geologizing. The house where we slept
was situated at the foot of a mountain, on the summit of
which are the mines of S. Pedro de Nolasko. Sir F. Head
marvels how mines have been discovered in such extraordinary
situations, as the bleak summit of the mountain of S.
Pedro de Nolasko. In the first place, metallic veins in this
country are generally harder than the surrounding strata:
hence, during the gradual wear of the hills, they project
above the surface of the ground. Secondly, almost every
labourer, especially in the northern parts of Chile, understands
something about the appearance of ores. In the great
mining provinces of Coquimbo and Copiapo, firewood is very
scarce, and men search for it over every hill and dale; and
by this means nearly all the richest mines have there been
discovered. Chanuncillo, from which silver to the value of
many hundred thousand pounds has been raised in the course
of a few years, was discovered by a man who threw a stone
at his loaded donkey, and thinking that it was very heavy, he
picked it up, and found it full of pure silver: the vein
occurred at no great distance, standing up like a wedge of
metal. The miners, also, taking a crowbar with them, often
wander on Sundays over the mountains. In this south part
of Chile, the men who drive cattle into the Cordillera, and
who frequent every ravine where there is a little pasture, are
the usual discoverers.
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