The
slimy disgusting Holuthuriae (allied to our star-fish), which the
Chinese gourmands are so fond of, also feed largely, as I am
informed by Dr. Allan, on corals; and the bony apparatus within
their bodies seems well adapted for this end. These holuthuriae,
the fish, the numerous burrowing shells, and nereidous worms, which
perforate every block of 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 12, 1836.
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, 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.
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