98 CORAL FORMATIONS. 
Quoy and Gaymard were the first authors who ascertained that 
reef-forming corals were confined to small depths, contrary to the 
account of Forster and the early navigators. ‘The mistake of previous 
voyagers was a natural one, for coral reefs were proved to stand in an 
unfathomable ocean; yet it was from the first a mere opinion, as the 
fact of corals growing at such depths had never been ascertained. It 
is now considered altogether probable that the bottom of the ocean is 
without life of any kind, or is but sparingly populated. The few 
Caryophylhe and other species which are met with in deep waters, 
have been shown to be sparsely scattered, mostly of small size, and 
nowhere form accumulations or beds. 
The above-mentioned authors, who explored the Pacific in the 
Uranie under D’Urville,* concluded from their observations that 5 or 
6 fathoms (30 or 36 feet) limited their downward distribution. Ehren- 
berg, 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 that the living clumps do 
not rise from a greater depth than 16 or 17 fathoms.t Mr. Darwin, 
who traversed the Pacific with Captain Fitzroy, R. N., gives 20 
fathoms as not too great a range, and mentions reported instances of 
growing reefs in 25 or even 30 fathoms. He states that in the Red 
Sea, according to Captain Morehead, living corals occur at 25 fathoms. 
At Keeling Atoll, growing corals are described by him as wholly dis- 
appearing beyond 20 fathoms; and at the Maldives and Chagos, at a 
less depth. Other facts brought forward by Mr. Darwin, relate to 
Caryophyllie and those species which have a wide range beyond reef- 
forming zoophytes. 
It thus appears that all recent investigators since Quoy and Gay- 
mard have agreed in assigning a comparatively small depth to grow- 
ing corals. ‘The observations on this point, made during the cruise 
of the Expedition, tend to confirm this opinion. ‘The conclusion 
is borne out by the fact that soundings in the course of the various 
and extensive surveys afford no evidence of growing coral beyond 
twenty fathoms. Where the depth was fifteen fathoms, coral sand 
and fragments were almost uniformly reported. Among the Feejee 
Islands, the extent of coral reef-grounds surveyed was many hundreds 
of square miles, besides the more careful examination of harbours. 
* Afterwards also in the Astrolabe. 
t S. Stutchbury, West of England Journal, i. 48. 
