TEXTURE AND COMPOSITION OF CORALS. 91 
Phosphate of magnesia - C ¢ - z 2-70 
Alumina (and iron) - - - - - 16-00 
Oxyd of iron - - - : - - 18°30 
In other analyses similar results were obtained, with sometimes a 
larger proportion of fluorids. 
The horny corals, (axes of Gorgonie and Antipathi,) were found by 
Hatchett to have nearly the constitution of ordinary horn.* 
The sea-water and the ordinary food of the polyps are evidently the 
source from which the ingredients of coral are obtained. As coral is 
an animal secretion, 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, 1s the lowest attribute of vitality. 
Neither is it at all necessary to inquire whether the lime in sea- 
water exists as carbonate or sulphate, or whether chlorid of calcium 
takes the place of these. Vitality may make from the elements pre- 
sent whatever results the functions of the animal require.t 
Various waters were collected in the vicinity of the coral islands, 
and at different distances from them, for the purpose of analysis and 
to compare the constitution of the sea in different 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 5 to 3's of all the ingredients in solution. Prof. Forchhammer 
has ascertained that around the West Indian seas, where corals abound, 
lime is not as abundant as elsewhere in the ocean, the proportion, 
according to five analyses, being 10,000 to 247; while in the Kattegat, 
where the rivers of the Baltic carry it in considerable quantities, the 
* Tbid, p. 56. 
+ If a drop of sea-water be slowly evaporated under a microscope of high power, 
crystals of selenite (sulphate of lime) are produced, having the 
annexed forms, the most common presented by native crystals 
of this mineral, as stated in works on mineralogy. On adding 
more water, they are again dissolved ; and this may be repeated 
indefinitely. These results would seem to indicate that the lime 
was mostly in the state of a sulphate. 
Mr. Darwin states the remarkable fact, described by Mr. 
Webster, (Voyage of the Chanticleer, il, 319,) that a deposit of 
salt and gypsum two feet thick occurs on the shores of Ascension, 
which was formed by the dash of the waves. Beautiful crystals of selenite were obtained 
by the writer in logs of half decomposed wood in the shore-cliffs near Callao, which were 
of similar origin. 
