CORAL REEFS OF TORRES STRAITS 225 



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 deter- 

 mined by future researches. It is still possible, however, that the sea- 

 water of Florida can not dissolve limestone and if this be true, the 

 lagoons of the Florida-Bahama region were not formed by marine solu- 

 tion; 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 Maer 

 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 forma- 

 tion of the numerous caverns seen in all limestone regions. It is evident 

 that the torrential rains of the wet season at Maer 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 Maer Island show that all spe- 

 cies can survive being in sea-water diluted with an equal volume of rain- 

 water for at least four and a half hours, and most of the forms can sur- 

 vive 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, Sympkyllia, which 



VOL. LXXXV. — 16. 



