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.
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