The evidence of recent elevation is here more satisfactory. The bay of San
Carlos is in most parts bounded by precipitous cliffs from about ten to
forty feet in height, their bases being separated from the present line of
tidal action by a talus, a few feet in height, covered with vegetation. In
one sheltered creek (west of P. Arena), instead of a loose talus, there was
a bare sloping bank of tertiary mudstone, perforated, above the line of the
highest tides, by numerous shells of a Pholas now common in the harbour.
The upper extremities of these shells, standing upright in their holes with
grass growing out of them, were abraded about a quarter of an inch, to the
same level with the surrounding worn strata. In other parts, I observed (as
at Pudeto) a great beach, formed of comminuted shells, twenty feet above
the present shore. In other parts again, there were small caves worn into
the foot of the low cliffs, and protected from the waves by the talus with
its vegetation: one such cave, which I examined, had its mouth about twenty
feet, and its bottom, which was filled with sand containing fragments of
shells and legs of crabs, from eight to ten feet above high-water mark.
From these several facts, and from the appearance of the upraised shells, I
inferred that the elevation had been quite recent; and on inquiring from
Mr. Williams, the Portmaster, he told me he was convinced that the land had
risen, or the sea fallen, four feet within the last four years. During this
period, there had been one severe earthquake, but no particular change of
level was then observed; from the habits of the people who all keep boats
in the protected creeks, it is absolutely impossible that a rise of four
feet could have taken place suddenly and been unperceived. Mr. Williams
believes that the change has been quite gradual. Without the elevatory
movement continues at a quick rate, there can be no doubt that the sea will
soon destroy the talus of earth at the foot of the cliffs round the bay,
and will then reach its former lateral extension, but not of course its
former level: some of the inhabitants assured me that one such talus, with
a footpath on it, was even already sensibly decreasing in width.