1836. ] CORAL FORMATIONS. 465 
These holuthurie, the fish, the numerous burrowing shells, and 
nereidous worms, which perforate every block of dead coral, 
must be very efficient agerts in producing the fine white mud 
which lies at the bottom and on the shores of the lagoon. A 
portion, however, of this mud, which when wet strikingly re- 
sembled pounded chalk, was found by Professor Ehrenberg ic 
be partly composed of siliceous-shielded infusoria. 
April 12th.—In the morning we stood out of the lagoon on 
our passage to the Isle of France. Iam glad we have visited 
these islands: such formations surely rank high amongst the 
wonderful objects of this world. Captain Fitz Roy found no 
bottom with a line 7200 feet in length, at the distance of only 
2200 yards from the shore ; hence this island forms a lofty sub- 
marine mountain, with sides steeper even than those of the most 
abrupt volcanic cone. The saucer-shaped summit is nearly ten 
miles across ; and every single atom,* from the least particle to 
the largest fragment of rock, in this great pile, which however 
is small compared with vefy many other lagoon-islands, bears 
the stamp of having been subjected to organic arrangement. We 
feel surprise when travellers tell us of the vast dimensions ot 
the Pyramids and other great ruins, but how utterly insignificant 
are the greatest of these, when compared to these mountains of 
stone accumulated by the agency of various minute and tender 
animals! This is a wonder which does not at first strike the 
.eye of the body, but, after reflection, the eye of reason. 
I will now give a very brief account of the three great classes 
of coral-reefs ; namely, Atolls, Barrier, and Fringing-reefs, and 
will explain my views { on their formation. Almost every 
voyager who has crossed the Pacific has expressed his unbounded 
astonishment at the lagoon-islands, or as I shall for the future 
call them by their Indian name of atolls, and has attempted 
some explanation. Even as long ago as the year 1605, Pyrard 
* J exclude, of course, some soil which has been imported here in vessels 
from Malacca and Java, and likewise some small fragments of pumice, 
drifted here by the waves. The one block of green-stone, moreover, on the 
northern island must be excepted. 
+ These were first read before the Geological Society in May, 1837, 
and have since been developed in a separate volume on the ‘Structure and 
Distribution of Coral Reefs.’ 
