r,
settling together in a heap, they formed a solid mass.

As the waters were contained in no bed, and were spread over every
part of the globe, they rushed where they liked, tearing from
the scarcely-formed rocks material with which to compose schists,
sandstones, and limestones. This the roving waves bore over the
submerged and now peaty forests, and deposited above them the elements
of rocks which were to superpose the coal strata. In course of time,
periods of which include millions of years, these earths hardened in
layers, and enclosed under a thick carapace of pudding-stone, schist,
compact or friable sandstone, gravel and stones, the whole of the
massive forests.

And what went on in this gigantic crucible, where all this vegetable
matter had accumulated, sunk to various depths? A regular chemical
operation, a sort of distillation. All the carbon contained in these
vegetables had agglomerated, and little by little coal was forming
under the double influence of enormous pressure and the high temperature
maintained by the internal fires, at this time so close to it.

Thus there was one kingdom substituted for another in this slow but
irresistible reaction. The vegetable was transformed into a mineral.
Plants which had lived the vegetative life in all the vigor of first
creation became petrified. Some of the substances enclosed in this
vast herbal left their impression on the other more rapidly mineralized
products, which pressed them as an hydraulic press of incalculable power
would have done.

Thus also shells, zoophytes, star-fish, polypi, spirifores, even fish
and lizards brought by the water, left on the yet soft coal their exact
likeness, "admirably taken off."

Pressure seems to have played a considerable part in the formation of
carboniferous strata. In fact, it is to its degree of power that are due
the different sorts of coal, of which industry makes use. Thus in the
lowest layers of the coal ground appears the anthracite, which, being
almost destitute of volatile matter, contains the greatest quantity
of carbon. In the higher beds are found, on the contrary, lignite and
fossil wood, substances in which the quantity of carbon is infinitely
less. Between these two beds, according to the degree of pressure to
which they have been subjected, are found veins of graphite and rich or
poor coal. It may be asserted that it is for want of sufficient pressure
that beds of peaty bog have not been completely ch