1889-90.] Dr J. Murray & Mr R. Irvine on Coral Reefs. 95 
the amount of carbonate of lime is so constantly low. The reaction 
between organic matter and the sulphates present in sea water, to 
which we have referred, tends also to keep the amount of carbonate 
of lime in solution at about one-half (0T2 grms.) of what it might 
contain (0*28 grms. per litre). This peculiarity of sea water, in 
taking up a large amount of amorphous carbonate of lime and 
throwing it out in the crystalline form accounts for the filling up of 
the interstices of massive corals with crystalline carbonate in coral 
islands and other calcareous formations, so that all traces may ulti- 
mately be lost of the original organic structure. 
Our experiments show that there is very great diversity as to the 
amount of carbonate of lime that will pass into solution in sea- 
water from various calcareous structures in a given time. As a rule, 
the more definitely crystalline the substance the less is it soluble. 
Crystalline calcspar is less soluble than massive varieties of coral, 
and these again less so than the more porous varieties. To a cer- 
tain extent, this variation may be accounted for by the amount of 
surface exposed to the solvent action of the water, which is much 
greater in porous coral than in calcspar ; but it is found that finely- 
powdered calcspar is less soluble than finely-powdered coral, and we 
have already noted that the amorphous or hydrated carbonate of 
lime is much more soluble than any other form of the substance. 
In shells and corals those layers which have been recently deposited 
by the animals are more rapidly removed in solution than those of 
older date, which have, in consequence, assumed a more crystalline 
structure. The rate of solution is also much greater when the water 
is constantly renewed than when the same water remains in contact 
with the coral, and the solution approaches to saturation. It appears, 
then, that those portions of a coral or shell that have been recently 
in direct life-connection with the organism are more soluble than 
those portions which are older, and have consequently largely passed 
into the crystalline condition. 
In conducting these various experiments with carbonate of lime, 
we were early led to suspect that different samples of sea water 
possessed very different solvent powers, and this was confirmed by 
special observations. For instance, water taken last summer (1889) 
from the German Ocean, 30 miles outside the Island, of May, had a 
very distinct solvent power on the corals exposed to its action, while 
