MODE OF FORMATION. 105 
Accumulations of fragments and sand from the coral zoophytes, and 
of shells and other relics of organic life, are in constant progress ; and 
thus a bed of coral debris is formed and compacted. There is this 
difference, that a large part of the vegetable material consists of ele- 
ments which escape as gases on decomposition, whereas coral is itself 
an enduring rock-material, undergoing no essential change except the 
mechanical one of comminution. ‘The animal portion is but a mere 
fraction of the whole zoophyte. 
In these few hints, we have the whole theory of reef-making : not 
a speculative opinion, but a legitimate deduction from a few simple 
facts, and bearing close analogy to operations on land. The coral 
debris and shells fill up the intervals between the coral patches, and 
the cavities among the living tufts, and in this manner produce the 
reef deposit, which is consolidated by the filtrating sea-water, hav- 
ing more or less lime in solution. The coral-zoophyte is especially 
adapted for such a mode of reef-accumulation. Were the nourish- 
ment drawn from below, as in most plants, the solidifying coral rock 
would soon destroy all life: instead of this, the tree is gradually dying 
below while growing above; and the accumulations cover only the 
dead portions. Moreover, to prevent accident, where these accumula- 
tions do not keep pace with the progress of death, organic incrusta- 
tions cover the lifeless trunk, and protect it from the dissolving waters. 
But on land, there is annual and also senile decay to produce vege- 
table debris; and lightning and storms prostrate forests. And are 
there any corresponding effects among the groves of the sea? It has 
been shown that coral plantations, from which reefs proceed, do not 
grow in the “calm and still” depths of the ocean. They are to be 
found amid the very waves, and extend but little below a hundred 
feet, which is far within the reach of the sea’s heavier commotions.* 
Here is an agent which is not without its effects. The enormous 
masses of uptorn rock found on many of the islands may give some 
* During the more violent gales, the bottom of the sea is said, by different authors, to 
be disturbed to a depth of three hundred, three hundred and fifty, or even five hundred 
feet, and De la Beche remarks, that when the depth is fifteen fathoms, the water is very 
evidently discolored by the action of the waves on the sand and mud of the bottom. In 
the Comptes Rendus, t. xii. 774, M. Siau mentions that parallel ridges are formed on the 
bottom, by the motion of the water, which may be readily distinguished at a depth of at 
least twenty meters. The hollows between such ridges or zones are occupied by the 
heavier substances of the bottom. Similar zones were distinguished at a depth of one 
hundred and eighty-eight meters, to the northwest of the St. Paul’s Roads. 
27 
