CORALS AND CORAL ISLANDS. 229 
cavities among the living tufts, and in this manner produce 
the reef deposit; and the bed is finally consolidated, while 
still beneath the water. 
The coral zoéphyte is especially adapted for such a mode 
of reef-making. Were the nourishment drawn from below, as 
in most plants, the solidifying coral rock would soon destroy 
all life: instead of this, the zoéphyte is gradually dying be- 
low while growing above; and the accumulations of débris 
cover only the dead portions. 
But on land, there is the decay of the year, and that of old 
age, producing vegetable debris; and storms prostrate forests. 
And there are 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 waves, and usually 
extend little below a hundred feet, which is far within the 
reach of the sea’s heavier commotions. To a considerable ex- 
tent they grow in the very face of the tremendous breakers 
that strike and batter as they drive over the reefs. 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 idea of the force of the lifting wave; and there are ex- 
amples on record, to be found in various treatises on Geology, 
of still more surprising effects. 
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 fath- 
oms, the water is very evidently discolored by the action of 
the waves on the sand and mud of the bottom. 
In an article on the Force of Waves, by Thomas Steven- 
son, of Edinburgh, published in the Transactions of the Royal 
