1888.] on Structure^ Origin, and Distribution of Coral Beefs^ dc, 257 



minerals, are there fonnd in great numbers. Almost all these things 

 are found occasionally in the other regions of the ocean's bed, but 

 their presence is generally masked by the accumulation of other 

 matters. In some regions Radiolarian and Diatom remains are 

 found in the greatest depths, and they too are subject to the 

 solvent power of sea water, but to a much less extent than carbonate 

 of lime shells. 



As we ascend to shallower waters, a few of the thicker shelled 

 specimens are met with at first, with lesser depths the carbonate of 

 lime shells increase in number, until in the shallower deposits the 

 remains of Pteropods, Heteropods, and the most delicate larval shells 

 are present in the deposit at the bottom. This gradation in the 

 appearance of the shells can be well seen in a series of soundings 

 at different depths around a volcanic cone, such as has been described 

 as forming the base of a coral atoll. There is no known way of account- 

 ing for this vertical distribution of these dead shells except by 

 admitting that they have been dissolved away in sinking through the 

 deeper strata of water, or shortly after reaching the bottom ; indeed, 

 an examination of the shells themselves almost sliows the process in 

 operation. It is rare to find any trace of fish bones in deposits other 

 than the otoliths. 



These considerations, as well as numerous experiments in the 

 laboratory, show that everywhere in the ocean dead carbonate of lime 

 structures slowly disappear wherever they are exposed to the action 

 of sea water, and in investigating the evolution of the general features 

 of coral reefs it is as necessary to take cognisance of this fact as of 

 the secretion of carbonate of lime by organisms. 



The first stage, then, in the history of a coral island is the pre- 

 paration of a suitable foundation on submerged volcanic cones, or 

 along the shores of a volcanic island, or the borders of a continent. 

 In the case of the atoll the cone may have been reduced below the 

 level of the sea by the waves and atmospheric influences, or built up 

 to the lower limit of breaker action by the vast accumulation of 

 organisms on its summit, 



A time comes, however, should the peak be situated in a region 

 where the temperature is sufiiciently high, and the surface currents 

 contain a suitable quality of food, that the reef-builders fix them- 

 selves on the bank. The massive structure which they secrete from 

 ocean water enables them to build up and maintain their position in 

 the very face of ocean currents, of breakers, of the overwhelming and 

 outrageous sea.* 



" Coral" with the sailor or marine surveyor is usually any carbonate 



* Dr. Brougham Guppy says, " History can afford us no clue to the first 

 appearance or tlie age of reefs ; yet in the mytlis of the Pacific Islanders we find 

 that the savage inhabitants of these regions regard the history of a coral atoll aa 

 commencing with the submerged shoal, which througli the agency of God-like 

 heroes is brought up by their fish-hooks to the surface." — Fajjer, Vict. Inst. 



