ANNIVERSARY ADDRESS OF THE PRESIDENT. xcv 
shore, according to the clearness of the water, though certainly here 
and there they seem to struggle hard with adverse conditions in this 
respect. Where by their increase the surf fails them, they seem to 
be soon covered by other corals and Nullipore ; the latter Mr. Dar- 
win points out as especially creeping over them towards the surf. 
When we consider that many a volcanic island rises through the sea 
by accumulating erupted masses of ashes, cinders and molten rock, 
and that the permanency of its continuance above the sea-level de- 
pends upon its power to resist the cutting and levelling action of 
the breakers, we perceive that such an accumulation may be either 
cut down entirely by this action, as that of Graham Island, 
which came through the waters of the Mediterranean in 1831, and 
now remains a shoal, or be notched by it, if the mass be sufficiently 
hard to resist entire removal. When partly cut back, the matter re- 
moved is distributed over the talus of the general volcanic protube- 
rance, not very materially increasing its angle of slope, since it would 
be piled over the talus much in the same manner as the detrital coral 
is accumulated in front of the coral reefs. The island reduced to a 
shoal would have the matter distributed over the flanks of the latter 
in the same manner, considering the accumulation to have been coni- 
cal, though more flat than the cones formed in the air. Supposing 
no subsidence, and this is by no means necessary, such a volcanic mass 
as Graham Island might be reduced to a shoal, the depth of which, 
beneath the surface, would correspond with the power of the waves 
during heavy gales of wind to remove ash and cinders from the top and 
scatter them over the sides, and we have the foundation for a coral reef. 
From the edge of a continuous or nearly continuous notch, due 
allowance being made for the effects of prevailing winds and break- 
ers round a volcanic island, keeping its main mass above the sea, 
there would be shallow water to the cliff or new shore, having a 
breadth depending upon the time the breakers have been employed 
in cutting it back, and upon the power of the rocks to resist this 
abrading force. In the case of the shoal there might be a coral 
reef having a round or oval form, or some modification of this form, 
according to circumstances, the habits of the reef-making corals 
causing them to work outwards, so that a kind of lagoon might be 
inside, especially if the old crater should permit a hollow to remain. 
In the case of the notched islands, the abrasion of the coast and 
the readiness with which detritus from it would be raised in me- 
chanical suspension by heavy gales, would cause the reef-making 
corals to keep the outer edge, where the proximity of the deep sea 
would give them clear water. Here once established they would 
form a barrier, and working outwards would cover the slope with 
their debris, and gradually rising would protect the island coasts from 
the heavy action of the breakers, which would then fall upon the coral 
reefs. These would correspond with the old shape of the island, and 
therefore would probably differ little from its shores, round which 
they would form an outer rampart with shallow water inside, better 
fitted for the presence of other corals and of molluscs and marine ani- 
mals loving quiet and clearer water, than could have been found over 
