Coral Reefs; Volcanic Islands; South American Geology — CompleteDarwin, Charles
Science
Coral Reefs; Volcanic Islands; South American Geology — Complete
Darwin, Charles
Beagle Expedition (1831-1836); Coral reefs and islands; Geology -- South America; Islands; Volcanoes
active volcanoes on the eastern side of Formosa. In Torres Straits, on
Cap Island (9° 48′ S., 142° 39′ E.) a volcano was seen burning with
great violence in 1793 by Captain Bampton (see Introduction to
Flinders’ “Voyage,” p. 41). Mr. M’Clelland (Report of Committee for
investigating Coal in India, p. 39) has shown that the volcanic band
passing through Barren Island must be extended northwards. It appears
by an old chart, that Cheduba was once an active volcano (see also _
Silliman’s North American Journal_, vol. xxxviii, p. 385). In
Berghaus’ “Phys. Atlas,” 1840, No. 7 of Geological Part, a volcano on
the coast of Pondicherry is said to have burst forth in 1757.
Ordinaire (“Hist. Nat. des Volcans,” p. 218) says that there is one at
the mouth of the Persian Gulf, but I have not coloured it, as he gives
no particulars. A volcano in Amsterdam, or St. Paul’s, in the southern
part of the Indian Ocean, has been seen (_Naut. Mag._ 1838, p. 842) in
action. Dr. J. Allan, of Forres, informs me in a letter, that when he
was at Joanna, he saw at night flames apparently volcanic, issuing
from the chief Comoro Island, and that the Arabs assured him that they
were volcanic, adding that the volcano burned more during the wet
season. I have marked this as a volcano, though with some hesitation,
on account of the possibility of the flame arising from gaseous
sources.
The uncoloured coasts consist, first and chiefly, of those, where there
are no coral-reefs, or such small portions as to be quite
insignificant. Secondly, of those coasts where there are reefs, but
where the sea is very shallow, for in this case the reefs generally lie
far from the land, and become very irregular, in their forms: where
they have not become irregular, they have been coloured. thirdly, if I
had the means of ascertaining the fact, I should not colour a reef
merely coating the edges of a submarine crater, or of a level submerged
bank; for such superficial
formations differ essentially, even when not in external appearance,
from reefs whose foundations as well as superficies have been wholly
formed by the growth of coral. Fourthly, in the Red Sea, and within
some parts of the East Indian Archipelago (if the imperfect charts of
the latter can be trusted), there are many scattered reefs, of small
size, represented in the chart by mere dots, which rise out of deep
water: these cannot be arranged under either of the three classes: in
the Red Sea, however, some of these little reefs, from their position,
seem once to have formed parts of a continuous barrier. There exist,
also, scattered in the open ocean, some linear and irregularly formed
strips of coral-reef, which, as shown in the last chapter, are probably
allied in their origin to atolls; but as they do not belong to that
class, they have not been coloured; they are very few in number and of
insignificant dimensions. Lastly, some reefs are left uncoloured from
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