77

. From long exposure to atmospheric influence, and other causes,
the shells have become disintegrated, and readily crumble on free
exposure to the air. Again, after the lapse of a considerable pe-
riod, they become very much disorganized by another process.
At first a little moss forms on the surface of the shells; this takes
up enough lime that has been dissolved by the carbonic acid of the
atmosphere to give support to a higher order of vegetation. This
vegetation, by its decay, furnishes food for a succeeding generation
of plants, and by an increased supply of carbonic acid dissolves
more lime to supply another generation. This, in its turn, dying",
furnishes increased means for the solution of the shell, until in many
cases these banks are covered with the most luxuriant vegetation,
and support large trees. The layer of matter covering the shells
is called "shell mould," and consists of shells in a very comminuted
state, and the organic and inorganic remains of the plants to which
it owes its formation. A little reflection will at once show, that
this mould must prove a most valuable manure, being nothing but
the remains, the ashes, so to speak, of plants, mixed with a large
quantity of oyster shells, in a very minute state of division.

This mould contains of air-slaked lime, by the average of 25
different analyses, about 45 6 per cent, being more than half as
good as common agricultural lime; and when we also consider the
other matters in this mould, the ratio to limestone is much increased.
It is almost needless to say that the lime in this mould is identical
with that in limestones, fresh shells, &c, and will act equally as
well. A custom has prevailed, to a very injurious extent, of apply-
ing the mould together with quantities of large, coarse fragments of
shells. I cannot too strongly reprobate this mode of using the
banks. These large fragments take up much space in the soil that
should be filled by other matter, injure its texture, and render the
crops grown on it very liable to burn or fire. Though these shells
be composed of lime, it is not available, but in a very slight degree,
to the use of crops. Lime, to be serviceable, must be in the state
of very fine powder, and intimately incorporated with the soil.
When it exists in shells of any size, it does almost no good by its
presence, and, as I have before said, injures the texture of the soil.
For all present practical purposes, pebble stones would be equally
beneficial.

The best way to use these shell banks is to have a sieve fixed
with a slight inclination. Against this the shells should be thrown,
as when persons wish to free sand from gravel. The fine particles
which pass through the sive should be applied as they are, whilst
the coarse shells which do not pass through, should be put into
kilns and burnt. In this way no part of these valuable deposits
would be lost; all would be saved for agricultural improvement,
thereby increasing the quantity of crops, and augmenting the value
of land, instead of retarding its improvement, as is the case when