On Coral Reefs and Islands. 83 
some circumstances, must have taken place,) is especially favora- 
ble for consolidation. When the coral is a fine mud, and the grains 
are therefore extremely fine, the dolomisation might extend to the 
grains themselves, as well as the infiltrating material acting as a 
cement. But when the grains of coral are large, or there are peb- 
bles, the infiltrated material that might be magnesian would con- 
stitute but a small part of the whole bed, Hence it is obvious 
that such formations in cold waters should not always in the 
mass have the proportions of a true dolomite, (54:2 of carbonate 
of lime, to 45-8 of carbonate of magnesia ;) they would probably 
attain such proportions under an ocean during that action of heat 
required alike for crystallization and chemical combination.* 
[. It is an inquiry of some interest, whether, in an archi- 
pelago like the Panmotus, coral. debris is not carried from the 
coral islands, and distributed over the bottom of the ocean ; and 
whether limestones thus originating, are not im process of forma- 
tion. [I venture no positive assertion on this subject, yet would 
express strong doubts. The fact that soundings off some islands, 
as we recede from the reef-growing depths, lose more and more 
in the proportion of coral sand, till we finally reach a bottom of 
earth, like the material of the island, bears against any such hy- 
pothesis. This was found to be the case off Upolu, where the 
reefs are extensive. 
The action of the waves tends to throw back the material 
2 into the sea by fresh water streams and other woaee 
from land debris of deep sea deposits, outside of soundings, is an 
i ved. Such results may 
pro 
perhaps take place off the mouths of large rivers like the Amazon, 
* Prof, Horsford, in a lidation of 1 reef-rock, read before 
: paper on the consolidation of coral ree 
the last meeting of the fi iati 
a nsolidation to the presence of org atter which undergoes decomposition, 
—, phur present produces sulphuretted hydroge: is € 
results hate of lime and a — wena < 
mmponia (r from itrogen) carries © sulphurie as sulphi 
oe tatmonla and leaves the lime as a i hydrate, which remains ‘iived with the 
Fuchs te of lime, forming a compound like that indicated as in mortar 
; the final removal of the water by evaporation leaves the ina mart 
= de level 
_ An the first place, his nly alludes to the rock formed above low-tide level, 
T have Falled the pot kg pew eae ” Kents, the amount of organic matter in 
ia this on found by analyses, does not exceed 5 per cent. and the sulpbur present 
“MS organic pons is ame: per 
But as the sands of t hich have a peculiar! y white and clean appear- 
washed he awed the animal matter they contain is either un- 
utter present cannot or is one of By the ween ofthe tides aon 
ontri nsolidation. The waters of the ces alo 
por on the open ooo is cocaity not been proved to carry in dissolved 
