Beagle Expedition (1831-1836); Coral reefs and islands; Geology -- South America; Islands; Volcanoes
remains have not been specifically examined; they may, therefore, and
especially the stratum observed by Mr. Stutchbury at an immense height,
be contemporaneous with the first formation of the Society Islands, and
be of any degree of antiquity; or they may have been deposited at some
subsequent, but probably not very recent, period of elevation; for if
the period had been recent, the entire surface of the coast land of
these islands, where the reefs are so extensive, would have been coated
with upraised coral, which certainly is not the case. Two of the
Harvey, or Cook Islands, namely, Aitutaki and Manouai, are encircled by
reefs, which extend so far from the land, that I have coloured them
blue, although with much hesitation, as the space within the reef is
shallow, and the outline of the land is not abrupt. These two islands
consist of coral-rock; but I have no evidence of their recent
elevation, besides, the improbability of Mangaia, a fringed island in
the same group (but distant 170 miles), having retained its nearly
perfect atoll-like structure, during any immense lapse of time after
its upheaval. The Red Sea, therefore, is the only area in which we have
clear proofs of the recent elevation of a district, which, by our
theory (although the barrier-reefs are there not well characterised),
has lately subsided. But we have no reason to be surprised at
oscillation, of level of this kind having occasionally taken place.
There can be scarcely any doubt that Savage, Aurora,[34] and Mangaia
Islands, and several of the islands in the Friendly group, existed
originally as atolls, and these have undoubtedly since been upraised to
some height above the level of the sea; so that by our theory, there
has here, also, been an oscillation of level, —elevation having
succeeded subsidence, instead of, as in the middle part of the Red Sea
and at the Harvey Islands, subsidence having probably succeeded recent
elevation.
[33] Ellis, in his “Polynesian Researches,” was the first to call
attention to these remains (volume i., page 38), and the tradition of
the natives concerning them. See also Williams, “Nar. of Missionary
Enterprise,” page 21; also Tyerman and G. Bennett, “Journal of
Voyage,” volume i., page 213; also Mr. Couthouy’s “Remarks,” page 51;
but this principal fact, namely, that there is a mass of upraised
coral on the narrow peninsula of Tiarubu, is from hearsay evidence;
also Mr. Stutchbury, “West of England Journal,” No. i., page 54. There
is a passage in Von Zach, “Corres. Astronom.” volume x., page 266,
inferring an uprising at Tahiti, from a footpath now used, which was
formerly impassable; but I particularly inquired from several native
chiefs, whether they knew of any change of this kind, and they were
unanimous in giving me an answer in the negative.
Public-domain text, read in full here on John Shaqi.
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