88 Fluor Spar, Apatite and Chondrodite in Limestone. 
Art. XIL—On the occurrence of Fluor Spar, Apatite and. Chon: 
drodite in Limestone ; by James D. Dana. 
Tue analyses of corals by Mr. B. Silliman, Jr.,* have — ae 
that although ordinary corals consist mainly of carbonate of lime, 
there is present a small proportion of phosphates, and fluorides, 
with some silica, alumina and oxyd of iron. It is also probable, 
from ‘some trials by Mr. Silliman, that these constituents exist 
also in many shells. 
From the results obtained in these analyses, it appears that the 
fluorides and phosphates amount, on an average, to about 4 per 
cent, or 0:25 parts in a hundred parts of coral; and the amount 
in the same manner of the phosphates, is 0 ‘05 per cent. A cuhie 
foot of coral; as deduced from the average specific gravity ascer- ; 
tained by Mr. Silliman, weighs: 157 pounds. Consequently in 
each cubic foot there are 6} ounces of fluorides, and 14 ounces 
of phosphates ; in each cubic rod, 1700 pounds of fluorides, and 
340 pounds of phosphates. These fluorides are fluorides of cal- . 
cium and magnesium, and the phosphates are phosphates of lime © 
and magnesia. Inthe same manner we ascertain that the amount 
of fluorides in a reef of coral, a mile long, half amile wide and 
a hundred feet. deep, amounts to more than 500, 000, 000 pounds. 
The proportion of silica is a little less than that of. the fluorides. 
Late geological researches have placed it beyond doubt, that 
the various limestones consist mainly, like coral. limestone, of ani- 
mal remains, among which corals, in. many instances, holds ‘acon- 
spicuous place.. These limestones often contain. erystallizations 
of fluoride of calcium (fluor spar); and in other beds which have ~ 
evidently been acted upon and crystallized by heat, there are also 
apatite (phosphate of lime), and chondrodite, (composed of fluorie 
acid, magnesia and silica). Moreover these are > the most com- 
moe minerals of these limestones. _ 
_ The above deductions supply us with a full explanation of ifs 
origin of these minerals. The fluorine, phosphoric acid, lime, - 
Magnesia and silica present, are adequate for all the results, with- 
_ out looking to any other sources. Instead therefore of being eX 
taneous minerals introduced | into the limestone rock, their ele- 
See he volume of e 
Fo bese sing Hee S 
he “Exploring Expedition on ‘Zoophytes, | p- 712; and this : 
ea ae es ae ene 
| 
