CORALS AND CORAL REEFS. 9 
action of the Humus Acids and Carbonic Acid upon the lime 
compounds in these rocks. 
(3) Seaward transportal of the dissolved products by 
rivers. 
(4) Conversion of the bicarbonate of lime into the sul- 
phate. 
(5) Diffusion of the sulphate through oceanic waters. 
(6) Assimilation of these lime-salts by organic agencies, 
which reconvert them into carbonate of lime, generally with 
the crystalline form of Aragonite, which is subsequently left 
upon the sea bottom over the areas where the depth does not 
exceed 1500 fathoms. 
(7) Concurrent precipitation of carbonate of lime, by the 
action of the waste-products of living organisms, and de- 
composing organic matter, upon the sulphate of lime in 
solution in sea-water. 
(8) Subsequent changes, ending in the upheaval of the 
sea bottom, the exposure of the newly-formed limestone to 
atmospheric agencies, its solution, transportal seawards, and 
the commencement of another cycle of change, as before. 
We are now in a position to consider corals in their 
biological aspect, so far as is needed for the purpose of the 
present Address. The animals that give rise to what we 
commonly understand by corals, belong to two groups of the 
Ceelentera. The structure of the soft parts of one of these 
may, for our present purpose, be likened to that of the 
common Fresh-Water Hydra; and that of the other group 
to the structure of any one of the well-known Sea Anemones. 
The chief point of difference that concerns us now between 
these familiar types of animal life and the animals that give 
rise to the coral structures, lies in the fact that little or no 
carbonate of lime accumulates in any part of the bodies of 
those typified by the Hydra and the Anemone. In the case 
of the coral animals, the solutions of sulphate of lime are 
converted, as Mr Irvine has shown us in the paper referred 
to above, into lime-soaps, and it is from the further action 
of organic agencies upon these emulsions that a deposit of 
minute granules of carbonate of lime takes place within the 
tissues of the lower part of the animal’s body.- These 
