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
beach-heads 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.
(PLATE 74. SOUTH AMERICAN BIT.)
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.
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