Page:Popular Science Monthly Volume 85.djvu/229

Rh bromites, finds that carbon dioxide is set free, and discharged into the air, from the Tortugas sea-water at ordinary atmospheric pressures and temperatures. The whole question as to the condition of the carbon dioxide within the ocean itself is therefore thrown open to be determined by future researches. It is still possible, however, that the seawater of Florida can not dissolve limestone and if this be true, the lagoons of the Florida-Bahama region were not formed by marine solution; but as yet no direct tests have been made to determine the efficacy of the water of the reefs as a limestone solvent, although the writer has begun a series of experiments to test this at Tortugas.

It seems that the limestone of the shallow southeast reef-flat of Maër Island must dissolve, for the disintegrated coral sand disappears in situ, there being very little sand either on the hard, rocky bottom of the lagoon or on the beach.

There are, however, several factors other than sea-water which might cause such solution, for it is well known that when rain-water percolates through dead leaves it gains a considerable charge of carbonic acid and this has been the cause of the solution which has resulted in the formation of the numerous caverns seen in all limestone regions. It is evident that the torrential rains of the wet season at Maër Island cause a great outpouring of fresh water from the shores over the reef flat and this must dissolve the limestone. This is not necessarily injurious to the living corals, however, for experiments made at Maër Island show that all species can survive being in sea-water diluted with an equal volume of rainwater for at least four and a half hours, and most of the forms can survive twelve hours of such treatment. The fact that there is but little coral sand along the southeast beach indicates that after it is cast ashore it is soon dissolved by the terrestrial drainage in the wet season.

There are, also, other agencies which dissolve limestone, for Professor Treadwell finds that worms which form burrows in dead coral heads are decidedly acid, and many sponges and boring plants are well known to dissolve the shells of molluscs. In addition, Stanley Gardiner, Wood-Jones, and others have observed that echinoderms which swallow large amounts of calcareous sand probably dissolve a certain percentage of it in their digestive tracts. We thus see that limestone is built up by some agencies and destroyed by others and the resultant condition of the reefs represents the balance between these antagonistic tendencies.

This leads us to the question of the rate of growth of corals, a subject which has been studied in greatest detail by Dr. Vaughan at Tortugas, Florida, and in the Bahamas, but upon which many other students have worked in a less exhaustive manner. For example, in 1890, Saville-Kent measured and photographed certain corals off Vivien Point, Thursday Island, and some of these we succeeded in identifying and remeasuring in November, 1913, and it appeared that a brain coral, Symphyllia, which