On Coral Reefs and Islands. 81 
of lime and magnesia. ‘To obtain the amount of these ingredi- 
ents in a reef a mile long, half a mile wide and a hundred feet 
deep, the estimate for a cubic rod should be multiplied by 320,000; 
which will give for the fluorids more than five hundred millions 
of pounds. : 
Late geological researches have placed it beyond doubt that 
the various limestones consist mainly, like coral limestone, of ani- 
mal remains, among which, in many instances, corals have a 
conspicuous place. These limestones often contain crystalliza- 
m 
instances) an essential part of its constitution. And they have 
en separated from the general mass by a segregation of like 
atoms, under well-known principles, while the rock was su 
jected to an elevated temperature. ‘The fluorid of calcinm ap- 
pears to crystallize without much heat; but apatite and chondro- 
dite are found mainly in granular limestones, which show, b 
their crystalline texture, that they have been subjected either 
to a very high temperature, or to one long continued of more 
moderate degree 
Lord Byron, of the Blonde, states that specimens of phosphate 
of lime (apatite,) were actually collected on Mauki, of the Her- 
vey Group, one of the elevated coral islands. . 
he cementation of coral sand along shores and beneath 
the sea is illustrated among all reefs, and is the process by which 
teef-rocks are formed. The sea-water receives some carbonate 
of lime into solution, and again deposits it among the deposited 
sand and fragments which lie compacted together. The same 
s place among the beach sands and the drift heaps. 
covered in part by a smooth, solid crust, two or three lines thick, 
ad made of injurk like stalagmite, which was formed by the so- 
lution of lime from the surface by the rains, and its deposition 
48810 on evaporation. 
The waters of the sea have been found to contain a small pro- 
Portion of free carbonic acid, which is sufficient to enable it to 
dissolve the carbonate of lime of the corals. 
Secon Sunres, Vol, XIV, No, ” aad 1852. it 
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