100 COBALS AND CORAL ISLANDS. 



ments present whatever results the functions of the animal re- 

 quire. 



The proportion of lime salts which occurs in the water of 

 the ocean is about §j to ^ of all the ingredients in solution. The 

 lime is mainly in the state of sulphate. Bischof states that the 

 proportion of salts of all kinds in sea- water averages 3"527 per 

 cent.; and in 100 parts of this, 75*79 are chloride of sodium, 

 9*16 chloride of magnesium, 3*66 chloride of potassium, 1*18 

 bromide of sodium, 4*62 sulphate of lime or gypsum, and 5*597 

 sulphate of magnesia, = 100. This corresponds to about 16^ 

 parts of sulphate of lime to 10,000 of water. 



Fluorine has also been detected in sea-water ; so that all the 

 ingredients of coral are actually contained in the waters of the 

 ocean. 



It has been common to attribute the origin of the lime of 

 corals to the existence of carbonic-acid springs in the vicinity 

 of coral islands. But it is an objection to such a hypothesis, 

 that, in the first place, the facts do not require it ; and, in the 

 second, there is no foundation for it. The islands have been 

 supposed to rest on volcanic summits, thus making one hy- 

 pothesis the basis of another. Carbonic-acid springs are by no 

 means a universal attendant on volcanic action. The Pacific 

 affords no one fact in support of such an opinion. There are 

 none on Hawaii, where are the most active fires in Polynesia ; 

 and the many explorations of the Society and Navigator Isl- 

 ands have brought none to light. Some of the largest reefs 

 of the Pacific, those of Australia and New Caledonia, oc- 

 cur where there is no evidence of former volcanic action. 



The currents of the Pacific are constantly bearing new sup- 

 plies of water over the growing coral beds, and the whole ocean 

 is thus engaged in contributing to their nutriment. Fish, mol- 

 lusks, and zoophytes are thus provided with earthy ingredi- 



