Beagle Expedition (1831-1836); Coral reefs and islands; Geology -- South America; Islands; Volcanoes
[25] Captain B. Hall, “Voyage to Loo Choo,” Append., pages xxi. and
xxv. Captain Beechey’s “Voyage,” page 496.
Dr. Davy[26] describes the northern province of _Ceylon_ as being very
low, and consisting of a limestone with shells and corals of very
recent origin; he adds, that it does not admit of a doubt that the sea
has retired from this district even within the memory of man. There is
also some reason for believing that the western shores of India, north
of Ceylon, have been upraised within the recent period.[27] _Mauritius_
has certainly been upraised within the recent period, as I have stated
in the chapter on fringing-reefs. The northern extremity of
_Madagascar_ is described by Captain Owen[28] as formed of madreporitic
rock, as likewise are the shores and outlying islands along an immense
space of _Eastern Africa_, from a little north of the equator for nine
hundred miles southward. Nothing can be more vague than the expression
“madreporitic rock;” but at the same time it is, I think, scarcely
possible to look at the chart of the linear islets, which rise to a
greater height than can be accounted for by the growth of coral, in
front of the coast, from the equator to 2° S., without feeling
convinced that a line of fringing-reefs has been elevated at a period
so recent, that no great changes have since taken place on the surface
of this part of the globe. Some, also, of the higher islands of
madreporitic rock on this coast, for instance Pemba, have very singular
forms, which seem to show the combined effect of the growth of coral
round submerged banks, and their subsequent upheaval. Dr. Allan informs
me that he never observed any elevated organic remains on the
_Seychelles_, which come under our fringed class.
[26] “Travels in Ceylon,” page 13. This madreporitic formation is
mentioned by M. Cordier in his report to the Institute (May 4th,
1839), on the voyage of the “Chevrette”, as one of immense extent, and
belonging to the latest tertiary period.
[27] Dr. Benza, in his “Journey through the N. Circars” (the “Madras
Lit. and Scient. Journ.” volume v.) has described a formation with
recent fresh-water and marine shells, occurring at the distance of
three or four miles from the present shore. Dr. Benza, in conversation
with me, attributed their position to a rise of the land. Dr.
Malcolmson, however (and there cannot be a higher authority on the
geology of India) informs me that he suspects that these beds may have
been formed by the mere action of the waves and currents accumulating
sediment. From analogy I should much incline to Dr. Benza’s opinion.
[28] Owen’s “Africa,” volume ii., page 37, for Madagascar; and for S.
Africa, volume i., pages 412 and 426. Lieutenant Boteler’s narrative
contains fuller particulars regarding the coral-rock, volume i., page
174, and volume ii., pages 41 and 54. See also Ruschenberger’s “Voyage
round the World,” volume i., page 60.
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