176 On Coral Reefs and Islands. 



ses, being 247 to 10,000 ; while in the Kattegat, where the rivers 

 of the Baltic carry it in considerable quantities, the proportion, 

 from four analyses, is 371 to 10,000.* Schweitzer obtained the 



t 



Grains. 



96474 



vv ater, • • , « • 



Chlorid of sodium, . . . . 27'06 



Chlorid of potassium, . ... 0-77 



Chlorid of magnesium, ,.' . • . 3 67 



Bromid of magnesium, . . 003 



Sulphate of magnesia, . . • 2*29 



Sulphate of lime, . . . l'4l 



Carbonate of lime, . . . . ' 0*03 



100000 



Recently, Mr. G. Wilson has detected fluorine in sea-water, 

 showing that all the ingredients of coral are actually contained 

 in the waters of the ocean.J 



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

 rals to the existence of carbonic acid springs in the vicinity of coral 

 islands. Bat it is an objection to such a hypothesis, that in the 

 first place the fads 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 hypothesis the basis of 

 another. Carbonic acid springs are by no means a universal at- 

 tendant 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 explora- 

 tions of the Society and Navigator Islands have brought noiie to 

 light. Some of the largest reefs of the Pacific, those of New 

 Holland and New Caledonia, occur 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- 

 luscs, and zoophytes are thus provided with earthy ingredients 

 for their calcareous secretions, if their food fails of giving the 

 necessary amount ; and by means of the powers of animal life 

 bones, shells, and corals alike are formed. 



The origin of the lime in solution throughout the ocean is an 

 inquiry foreign to our present subject- It is sufiicient here to 

 show that this lime, whatever its source, is adequate to explain 

 all the results under consideration. - 



; 



* On Comparative Analytical Researches on Sea-water, by Prof. Forclilianiiner, 

 ■Eep. Brit. Assoc, for 1846, p. 90. 



f Lond anil Ed. Phil. Mag. for July, 1839, xr, 51 ; Araer. .Tour. Sci., xxxviii, 12, 

 ' Trans. Roy. Soc. of Edinburg, xvi, 145, 1846 ; Am. Jour. ScL, 2d ser., ii, 114, 1846. 



See also Darwin, op. cit., p. 60. 



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