Corals and coral islands.

RANGE IN DEPTH OF CORALS.

115

Ehrenberg, by his observations on the reefs of. the Red Sea,
confirmed the observations of Quoy and Gaymard; he concluded that living corals do not occur beyond six fathoms. Mr.
Stutchbury, after a visit to some of the Paumotus and Tahiti,
remarks, in Volume I. of the West of England Journal, that
the living clumps do not rise from a greater depth than 16 or
17 fathoms.
Mr. Darwin, who traversed the' Pacific with Captain Fitzroy, R. N., gives 20 fathoms as not too great a range.
In his soundings off the fringing reefs of Mauritius, in
the Indian ocean, on the leeward side of the island, he observed especially two large species of Madrepores, and two
of Astreea; and a Millepora down to fifteen fathoms, with
also, in the deeper parts, Seriatopora; between fifteen and
twenty fathoms a bottom mostly of sand, but partly covered
with the Seriatopora, with a fragment of one of the Madrepores at twenty fathoms. He states that Capt. Moresby, in
his survey of the Maldives and Chagos group, found, at seven
or eight fathoms, great masses of living coral; at ten fathoms,
the same in groups with patches of white sand between; and,
at a little greater depth, a smooth steep slope without any
living coral; and further, on the Padua Bank, the northern
part of the Laccadive group, which had a depth of twenty-five
to thirty-five fathoms, he saw only dead coral, while on other
banks in the same group ten or twelve fathoms under water,
there was growing coral.
In the Red Sea, however, according to Capt. Moresby and
Lient. Wellstead, there are, to the north, large beds of living
corals at a depth of twenty-five fathoms, and the anchors were
often entangled by them; and he attributes this depth, so
much greater than reported by Ehrenberg, to the peculiar purity, or freedom from sediment, of the waters at that place. Kot