100 CORAL FORMATIONS. 
the capes of Oafonu harbour, on the same island, there was no coral, 
with a depth of fifteen fathoms. 
Similar results were obtained about all the islands surveyed, as the 
charts satisfactorily show. There is hence little room to doubt that 
twenty fathoms may be received as near the range in depth for reef 
corals ; and probably the limit lies between fifteen and twenty fathoms, 
or not far from one hundred feet. 
It may be here remarked, that soundings with reference to this 
subject are liable to be incorrectly reported by persons who have not 
particularly studied living zoophytes. It is of the utmost importance, 
in order that an observation supposed to prove the occurrence of living 
coral should be of any value, that it be unequivocally determined 
whether the fragments which a lead may bring up are alive or not 
when broken off; for a dead fragment proves nothing. Even a strong 
impression upon the lead, showing the form and character of the 
surface-cells of a coral, is not wholly satisfactory, as it may have been 
given by a mass not living. A living fragment, placed in water, will 
be seen to have a fleshy surface, even if the polyps do not expand. 
The best observations with reference to this subject would be made 
with a diving bell. 
Much yet remains for farther investigation. Mr. Edward Forbes, 
in his Zoological Explorations of the A%gean, distinguished three 
separate regions of invertebrate species within twenty fathoms of the 
surface: the /jirst, or littoral, extending to two fathoms in depth; the 
second from two to ten fathoms; the ¢hird from ten to twenty fathoms.* 
Similar subdivisions, or others on the same general principle, may 
yet be detected in the Pacific, indicated perhaps by zoophytes as well 
as molluscs. There is no evidence, however, that there are successive 
beds, composed of a distinct set of species, as has been sometimes 
suggested. ‘The upraised reefs of Metia afford no proofs of such a 
mode of formation; on the contrary, they show that the process is 
continuous and uniform in character through the reef-growing depths. 
The species in the lower part of the sixteen fathoms are probably 
different from many of those above; but they pertain to the same 
genera in most instances, and moreover there are no abrupt transitions ; 
consequently the resulting reefs should have a nearly uniform cha- 
racter, as here stated. This fact may be better appreciated after 
perusing the following chapter. 
* On the AXgean Invertebrata, E. Forbes, Rep. Brit. Assoc. for 18438, p. 154. 
