This is confirmed in examining those bodies of
fossil coal; for, though there are often found beds of sand-stone
immediately above and below the stratum of the coal, we do not find any
sand mixed in the strata of the coal itself.
Having found the composition of coal to be various, but all included
within certain rules which have been investigated, we may perceive in
this an explanation of that diversity which is often observed among the
various strata of one bed of coal. Even the most opposite species of
composition may be found in the thickness of one bed, although of very
little depth, that is to say, the purest bituminous coal may, in the
same bed, be conjoined with that which is most earthy.
Fossil coal is commonly alternated with regular sand-stone and
argillaceous strata; but these are very different bodies; therefore,
it may perhaps be inquired how such different substances came to be
deposited in the same place of the ocean. The answer to this is easy; we
do not pretend to trace things from their original to the place in which
they had been ultimately deposited at the bottom of the sea.
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