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 vegeta-tive
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 changed into coal.
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