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.
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