the main ingredient is particles of iron, (the iron black band.) The
secondary rocks are quite as communicative with regard to their
portion of the earth's history as the primitive were.

The first, or lowest, group of the secondary rocks is called the
Carboniferous Formation, from the remarkable feature of its numerous
interspersed beds of coal. It commences with the beds of the
MOUNTAIN LIMESTONE, which, in some situations, as in Derbyshire and
Ireland, are of great thickness, being alternated with chert (a
siliceous sandstone), sandstones, shales, and beds of coal, generally
of the harder and less bituminous kind (anthracite), the whole being
covered in some places by the millstone grit, a siliceous
conglomerate composed of the detritus of the primary rocks. The
mountain limestone, attaining in England to a depth of eight hundred
yards, greatly exceeds in volume any of the primary limestone beds,
and shews an enormous addition of power to the causes formerly
suggested as having produced this substance. In fact, remains of
corals, crinoidea, and shells, are so abundant in it, as to compose
three-fourths of the mass in some parts. Above the mountain
limestone commence the more conspicuous COAL BEDS, alternating with
sandstones, shales, beds of limestone, and ironstone. Coal is
altogether composed of the matter of a terrestrial vegetation,
transmuted by pressure. Some fresh-water shells have been found in
it, but few of marine origin, and no remains of those zoophytes and
crinoidea so abundant in the mountain limestone and other rocks.
Coal beds exist in Europe, Asia, and America, and have hitherto been
esteemed as the most valuable of mineral productions, from the
important services which the substance renders in manufactures and in
domestic economy. It is to be remarked, that there are some local
variations in the arrangement of coal beds. In France, they rest