dead coral, must be very efficient agents in producing the fine white
mud which lies at the bottom and on the shores of the lagoon. A
portion, however, of this mud, which when wet resembled pounded chalk,
was found by Professor Ehrenberg to be partly composed of
siliceous-shielded infusoria.
April 12th.--In the morning we stood out of the lagoon on our passage
to the Isle of France. I am glad we have visited these islands: such
formations surely rank high amongst the wonderful objects of this
world. Captain Fitz Roy found no bottom with a line 7200 feet in
length, at the distance of only 2200 yards from the shore; hence this
island forms a lofty submarine mountain, with sides steeper even than
those of the most abrupt volcanic cone. The saucer-shaped summit is
nearly ten miles across; and every single atom, [10] from the least
particle to the largest fragment of rock, in this great pile, which
however is small compared with very many other lagoon-islands, bears
the stamp of having been subjected to organic arrangement. We feel
surprise when travellers tell us of the vast dimensions of the Pyramids
and other great ruins, but how utterly insignificant are the greatest
of these, when compared to these mountains of stone accumulated by the
agency of various minute and tender animals! This is a wonder which
does not at first strike the eye of the body, but, after reflection,
the eye of reason.
I will now give a very brief account of the three great classes of
coral-reefs; namely, Atolls, Barrier, and Fringing-reefs, and will
explain my views [11] on their formation. Almost every voyager who has
crossed the Pacific has expressed his unbounded astonishment at the
lagoon-islands, or as I shall for the future call them by their Indian
name of atolls, and has attempted some explanation. Even as long ago
as the year 1605, Pyrard de Laval well exclaimed, "C'est
[picture]
une merveille de voir chacun de ces atollons, environne d'un grand banc
de pierre tout autour, n'y ayant point d'artifice humain." The
accompanying sketch of Whitsunday Island in the Pacific, copied from,
Capt. Beechey's admirable Voyage, gives but a faint idea of the
singular aspect of an atoll: it is one of the smallest size, and has
its narrow islets united together in a ring. The immensity of the
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