1888.] Messrs Irvine and Young on Carhonatc of Lime. 317 
At the greatest depths of the ocean all these calcareous shells dis- 
appear from the deposits in all latitudes. The cause of this in my 
opinion is, not that deep sea water contains any abnormal proportion 
of loose or free carbonic acid (Buchanan’s analysis tend to prove 
the erroneousness of such a presumption), but the fact that even 
alkaline sea water, if given sufficient time, will take up carbonate 
of lime in addition to what it already contains. The foraminiferal 
shells disappear at great depths, because it took them so long to 
reach these depths, they had time to pass into solution.” 
With the view of bringing this solubility of carbonate of lime to 
bear upon Dr John Murray’s theory as to the formation of coral 
island lagoons, a series of experiments was undertaken, the results 
of which are shown on the accompanying tables (p. 318). 
In conducting these experiments we endeavoured to imitate, as 
far as possible, the conditions under which such solvent action would 
be exerted on the material of coral reefs. We found a marked 
difference in the solubility of various corals, those of a porous 
nature dissolving to a much greater extent than the dense varieties. 
The reason for this is obvious. Xot only is a larger surface pre- 
sented to the action of the water, but the carbonate of lime (com- 
posing the coral) appears to be in a different molecular condition, 
being in the one case wholly or partially amorphous, and in the 
other massive or marble-like in structure. This difference in solu- 
bility between the different forms which carbonate of lime assumes 
is very marked. For instance, one part of precipitated amorphous 
carbonate of lime dissolving in 1600 parts of sea water, whilst one 
part of the same precipitated carbonate of lime, after it has passed 
from the amorphous to the crystallised condition, requires 8000 
parts of sea water to effect its solution. This is well borne out by 
the results obtained in treating soft and hard petrified coral, as 
shown in Table I. Moreover, porous corals, as a rule, contain a 
large proportion of organic matter, which in oxidising, after the 
coral is dead, produces carbonic acid, and this, dissolving in the 
water, exalts its solvent action. This is shown by the results of 
the experiments made with mussels, oysters, and other shell-fish, 
which were allowed to rot under sea water (see Table II.), the 
amount of lime passing into solution in these circumstances being 
very great. 
