been formed by the sea, during the gradual rising of the land. This
certainly is the true explanation, for I found numerous shells of
existing species on these terraces. Five narrow, gently sloping,
fringe-like terraces rise one behind the other, and where best
developed are formed of shingle: they front the bay, and sweep up both
sides of the valley. At Guasco, north of Coquimbo, the phenomenon is
displayed on a much grander scale, so as to strike with surprise even
some of the inhabitants. The terraces are there much broader, and may
be called plains, in some parts there are six of them, but generally
only five; they run up the valley for thirty-seven miles from the
coast. These step-formed terraces or fringes closely resemble those in
the valley of S. Cruz, and, except in being on a smaller scale, those
great ones along the whole coast-line of Patagonia. They have
undoubtedly been formed by the denuding power of the sea, during long
periods of rest in the gradual elevation of the continent.
Shells of many existing species not only lie on the surface of the
terraces at Coquimbo (to a height of 250 feet), but are embedded in a
friable calcareous rock, which in some places is as much as between
twenty and thirty feet in thickness, but is of little extent. These
modern beds rest on an ancient tertiary formation containing shells,
apparently all extinct. Although I examined so many hundred miles of
coast on the Pacific, as well as Atlantic side of the continent, I
found no regular strata containing sea-shells of recent species,
excepting at this place, and at a few points northward on the road to
Guasco. This fact appears to me highly remarkable; for the explanation
generally given by geologists, of the absence in any district of
stratified fossiliferous deposits of a given period, namely, that the
surface then existed as dry land, is not here applicable; for we know
from the shells strewed on the surface and embedded in loose sand or
mould that the land for thousands of miles along both coasts has lately
been submerged. The explanation, no doubt, must be sought in the fact,
that the whole southern part of the continent has been for a long time
slowly rising; and therefore that all matter deposited along shore in
shallow water, must have been soon brought up and slowly exposed to the
wearing action of the sea-beach; and it is only in comparatively
shallow water that the greater number of marine organic beings can
flourish, and in such water it is obviously impossible that strata of
any great thickness can accumulate. To show the vast power of the
wearing action of sea-beaches, we need only appeal to the great cliffs
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