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.
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