100 CORALS 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 | 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, 
916 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 164 
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 zoéphytes are thus provided with earthy ingredi- 
