Beagle Expedition (1831-1836); Coral reefs and islands; Geology -- South America; Islands; Volcanoes
dry at low water, and which on the outside rise abruptly from a deep
sea: on their insides they are separated from the continent by a
channel, or rather a succession of bays, with an average depth of ten
fathoms. The small headlands on the continent also have coral-banks
attached to them; and the Querimba islands and banks are placed on the
lines of prolongation of these headlands, and are separated from them
by very shallow channels. It is evident that whatever cause, whether
the drifting of sediment or subterranean movements, produced the
headlands, likewise produced, as might have been expected, submarine
prolongations to them; and these towards their outer extremities, have
since afforded a favourable basis for the growth of coral-reefs, and
subsequently for the formation of islets. As these reefs clearly belong
to the fringing class, the Querimba islands have been coloured
red.—_Monabila_ (13° 32′ S.). In the plan of this harbour, the
headlands outside are fringed by reefs apparently of coral; coloured
red.—_Mozambique_ (150° S.) The outer part of the island on which the
city is built, and the neighbouring islands, are fringed by
coral-reefs; coloured red. From the description given in Owen’s “Narr.”
(volume i., page 162), the shore from _Mozambique_ to _Delagoa Bay_
appears to be low and sandy; many of the shoals and islets off this
line of coast are of coral-formation; but from their small size and
lowness, it is not possible, from the charts, to know whether they are
truly fringed. Hence this portion of coast is left uncoloured, as are
likewise those parts more northward, of which no mention has been made
in the foregoing pages from the want of information.
PERSIAN GULF.—From the charts lately published on a large scale by the
East India Company, it appears that several parts, especially the
southern shores of this gulf, are fringed by coral-reefs; but as the
water is very shallow, and as there are numerous sandbanks, which are
difficult to distinguish on the chart from reefs, I have not coloured
the upper part red. Towards the mouth, however, where the water is
rather deeper, the islands of _Ormuz_ and _Larrack_, appear so
regularly fringed, that I have coloured them red. There are certainly
no atolls in the Persian Gulf. The shores of _Immaum_, and of the
promontory forming the southern headland of the Persian Gulf, seem to
be without reefs. The whole S.W. part (except one or two small patches)
of _Arabia Felix_, and the shores of _Socotra_ appear from the charts
and memoir of Captain Haines (“Geographical Journal,” 1839, page 125)
to be without any reefs. I believe there are no extensive coral-reefs
on any part of the coasts of _India_, except on the low promontory of
_Madura_ (as already mentioned) in front of Ceylon.
Public-domain text, read in full here on John Shaqi.
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