This will appear by
considering, that we find schistus mixed with coal in the most equal or
uniform manner, and in almost every conceivable degree, from the purest
coal to the most perfect schistus. Hence we have reason to conclude,
that, at the formation of those strata, the bituminous matter, highly
subtilised, had been uniformly mixed with the earth subsiding in the
water.
Not only is the bituminous matter of coal found mixed in every different
proportion with the earthy or uninflammable materials of strata, but the
coaly or bituminous composition is found with perhaps every different
species of substance belonging to strata. This is certain, that we have
the coaly matter intimately mixed with argillaceous and with calcareous
strata.
Thus it will appear, that it is no proper explanation of the formation
of coal strata, to say that vegetable matter is the basis of those
strata; for though, in vegetation, a substance proper for the formation
of bituminous matter is produced, it remains to know by what means, from
a vegetable body, this bituminous matter is produced, and how it comes
to be diffused in that subtile state by which it may be uniformly mixed
with the most impalpable earth in water.
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