upon the wall-like face of the reef, but on the ordinary shelving
sea-bottom. And the distance to which a fringing reef extends from the
land corresponds with that at which the sea has a depth of twenty or
five-and-twenty fathoms.

If, as we have supposed, the sea could be suddenly withdrawn from
around an island provided with a fringing reef, such as the Mauritius,
the reef would present the aspect of a terrace, its seaward face,
100 feet or more high, blooming with the animal flowers of the coral,
while its surface would be hollowed out into a shallow and irregular
moat-like excavation.

The coral mud, which occupies the bottom of the lagoon, and with which
all the interstices of the coral skeletons which accumulate to form
the reef are filled up, does not proceed from the washing action of
the waves alone; innumerable fishes, and other creatures which prey
upon the coral, add a very important contribution of finely-triturated
calcareous matter; and the corals and mud becoming incorporated
together, gradually harden and give rise to a sort of limestone rock,
which may vary a good deal in texture. Sometimes it remains friable
and chalky, but, more often, the infiltration of water, charged with
carbonic acid, dissolves some of the calcareous matter, and deposits
it elsewhere in the interstices of the nascent rock, thus glueing
and cementing the particles together into a hard mass; or it may even
dissolve the carbonate of lime more extensively, and re-deposit it in
a crystalline form. On the beach of the lagoon, where the coral sand
is washed into layers by the action of the waves, its grains become
thus fused together into strata of a limestone, so hard that they
ring when struck with a hammer, and inclined at a gentle angle,
corresponding with that of the surface of the beach. The hard parts