ANNIVERSARY ADDRESS OF THE PRESIDENT. xc 
of the coral pebbles, sands and finer calcareous mud towards the 
shore, where all such would be sorted and deposited in the usual 
manner. Detritus from the land would mingle with the calcareous 
sediments towards the coast, and especially when any was forced out 
of river-mouths, where, and in other sheltered situations, those de- 
tritus-collecting plants, the mangrove-trees, appear to be, from the 
descriptions of Mr. Beete Jukes, very common. 
Respecting the volume of this accumulation, including any detritus 
obtained from the shores, chiefly, it would appear, granitic, and even 
supposing it to repose on a sea-bottom gradually sloping to the great 
depths found immediately outside the great barrier reef, we have to 
measure it by no small amount of cubic miles. If to this we add the 
mass of similarly formed matter now constituting the atolls or lagoon- 
islands, the encircling reefs and the shore reefs of the Indian and 
Pacific Oceans, and now constantly increasing, the various coral and 
other germs settling and flourishing wherever they find the conditions 
suited to them, we have an immense mass of carbonate of lime 
transformed from a state of solution to that of a solid by the agency 
of animal life, adding most materially to the rocks now accumulating 
in the tropical regions of our globe. 
When we consider that heavy breakers are favourable to, and do 
not impede, the growth of certain corals, indeed such situations must 
prevent the attacks of many coral-feeding animals which would other- 
wise crop down the polyps and their fragile cells ; and that the germs 
of the surf-loving corals are floating about ready to settle wherever 
the sea is clear enough, and the temperature and other general con- 
ditions are suited to their growth, there seems little limit to their 
extension where such conditions obtam. These existing, a reef is 
formed, and the mechanical destruction of portions of it follow. If 
the power of the polyps to secrete their harder parts be as a whole 
greater than that of the surf to break them off,—the parts which can 
be broken off falling into deep water beyond the range of surf, and 
part ground down within its influence into sand, the general mass 
increases. 
The reason why the great barrier reef is interrupted off the southern 
coast of New Guinea,—for the coral conditions, and with them the 
coral reefs, again obtain on its western shores,—would appear to be 
made apparent by the voyage of the ‘Fly.’ A bottom of mud, the 
sediment from some great river or rivers flowing into the sea out of 
this part of New Guinea, extends over the ground which we can 
scarcely doubt would be occupied by coral reefs if the waters were 
clear. These muddy waters, every gale of wind stirring up the bot- 
tom for a long distance out, effectually keep off the coral growth ; and 
clays, by the accumulation of the mud where it can find sufficient 
repose, represent in geological time the calcareous accumulations on 
each side, any difference which such conditions make being im- 
pressed upon the animal life, remains of which are being entombed 
in the different parts of the general sea-bottom. 
Mr. Beete Jukes shows that at Erroob and the Murray Islands 
there has probably been igneous action during at least the formation 
