Geological Observations on South America — John Shaqi
Geological Observations on South AmericaDarwin, Charles
Science
Geological Observations on South America
Darwin, Charles
Beagle Expedition (1831-1836); Geology -- South America; Mollusks, Fossil -- South America; Paleontology
Commencing at the south and proceeding northward, the first place at
which I landed, was at Cape Tres Montes, in latitude 46 degrees 35′.
Here, on the shores of Christmas Cove, I observed in several places a
beach of pebbles with recent shells, about twenty feet above high-water
mark. Southward of Tres Montes (between latitude 47 and 48 degrees),
Byron remarks, “We thought it very strange, that upon the summits of
the highest hills were found beds of shells, a foot or two thick.”
(“Narrative of the Loss of the ‘Wager’.”) In the Chonos Archipelago,
the island of Lemus (latitude 44 degrees 30′) was, according to M.
Coste, suddenly elevated eight feet, during the earthquake of 1829: he
adds, “Des roches jadis toujours couvertes par la mer, restant
aujourd’hui constamment decouvertes.” (“Comptes Rendus” October 1838
page 706.) In other parts of this archipelago, I observed two terraces
of gravel, abutting to the foot of each other: at Lowe’s Harbour (43
degrees 48′), under a great mass of the boulder formation, about three
hundred feet in thickness, I found a layer of sand, with numerous
comminuted fragments of sea-shells, having a fresh aspect, but too
small to be identified.
THE ISLAND OF CHILOE.
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.
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account