Actions of Volcanoes. 295 
geologists may permit, according to their several views or pre- 
judices. But there remains a chemical question respecting the 
generation of coral islands, which is extremely obscure, but 
which is also highly interesting, not only as it relates to the 
production or collection of these enormous masses of calcareous 
earth, but as it bears on the formation of the ordinary stratified 
limestones. 
There is, in the first place, neither proof nor probability that 
lime is the produce of animal action, as has been supposed by 
some persons. The recent discoveries respecting the nature 
of the earths, must, indeed, have set this question at rest. 
Whatever difficulties may be found in the supposition, itis pro- 
bable that it is, in these cases, procured from the decomposition 
of the calcareous salts of the ocean; and, however, we may 
choose to foresee a period when that supply must cease, we 
must be content for the present to rest in the belief that this 
is its real origin, without inquiring further what, or whether 
any, provision is made for its perpetual renewal. 
But it is sufficient for the present object, to point out the 
enormous masses of calcareous matter thus produced, as we 
are, in this case, very sure that it is, by the mere operations of 
animals. If the bulks of Tongataboo, and ef the great coral 
reef of New Holland, be estimated by their extent and depth, 
as already stated, it will be seen that they are equivalent to 
some of the largest deposits of secondary limestone with which 
we are acquainted. The latter will bear a comparison even 
with the great ridges of the Jura, or the Apennines. That sup~ 
position of some geologists, that the secondary limestones have 
been produced by the animals whose shells are still imbedded 
in them, is far therefore from being so absurd as it has some- 
times been considered. It is certainly not necessary to imagine 
that all limestones have originated in the same sources; but 
when we recollect that these rocks abound among the secondary 
strata, while they are comparatively rare among the primary, 
diminishing in quantity in proportion as we recede from those 
periods in which the earth was inhabited, we contemplate a fact 
which cannot be looked on with indifference. 
