On Coral Reefs and Islands. 



175 



^ 



hundred parts of the same, subjected to exact analysis^ gave the 

 following result : 



Silicaj 



Magnesia, 



Fluorid of calcium, 

 Fluorid of magnesium, 

 Phosphate of magnesia, 

 Alumina (and iron), , 

 Oxyd of iron, . 



2200 



1303 



7-66 



7-83 

 12-48 



2T0 

 16-00 



18-30 



In other analyses similar results were obtained, with sometimes 

 a larger proportion of fluorids. 



The horny corals, (axes of Gorgonias and Antipathi,) were found 

 by Hatchelt to have nearly the constitution of ordinary horn.* 



The sea-water and the ordinary food of the polyps are evi- 

 dently the source from which the ingredients of coral are ob- 

 tained. As coral is an animal secretionj there is no good reason 

 for the surprise with which this subject is sometimes approached. 

 The same powers of elaboration which exist in other animals 

 belong to polyps; for this function, as we have remarked, is the 

 lowest attribute of vitahty. 



Neither is it at all necessary to inquire whether the lime in sea- 

 water exists as carbonate or sulphate, or whether chlorid of cal- 

 cium takes the place of these- The powers of life may make 

 from the elements present whatever results the functions of the 

 animal require.f 



Various waters were collected in the vicinity of the coral isl- 

 ands, and at different distances from them, for the purpose of 

 analysis in order to compare the constitution of the sea in differ- 

 ent parts ; but they were lost with the Peacock on the bar of the 

 Columbia river. The proportion of lime salts which occurs in the 

 Water of the ocean is about ^^ to ^j of all the ingredients in so- 



hition. 

 West 



Prof. Forchhammer has ascertained that around the 



as elsewhere in the ocean, the proportion, according to five analy- 



Report on Zoopliytes, p. 56. 

 t It a drop of sea-water be slowly evaporated under a microscope of high power, 

 crystals of selenite (sulphate of lime) are produced, hav- 

 ing the annexed forms, the most common presented by 

 ative crystals of this mineral, as stated in works on min- 

 eralogy. On adding more water, they are again dis- 

 8«>|ved ; and this may be repeated indetinitely. These re- 

 8«Us would seem to indicate that the lime was mostly in 

 the state of a sulphate. 



^^^f- I^^rwin states the remarkable iixct, described by 

 ^' Webster, (Voyage of the Chanticleer, ii, 319,) that a 

 ^posit of salt and gypsum two feet thick occurs on the 

 snores of Ascension, which was formed by the dash of 

 h if^^^^®' Beautiful crystals of selenite were obtained by the writer in logs of 

 '^^ decomposed wood in the shore cliflfs near Callao, which were of similar origin. 



