But this is the
description of our purest fossil coals, which burn in giving the
greatest quantity of heat, and leave the smallest quantity of ashes.
In order to form another regular species of coal, let us suppose that,
along with the bituminous substance now considered, there shall be
floating in the water of the ocean a subtile earthy substance, and that
these two different substances shall subside together in an uniform
manner, to produce a stratum which shall be covered with immense weight,
compressed, condensed, and consolidated as before, we should thus have
produced a most homogeneous or uniform body to appearance, but not so
in reality. The mixture of heterogeneous matter, in this case, is too
minute to be discovered simply by inspection; it must require deep
reflection upon the subject, with the help of chemical analysis,
to understand the constitution of this body, and judge of all the
circumstances or particulars in which it differs from the former. It is
worth while to examine this subject with some attention, as it will give
the most instructive view of the composition of bituminous strata, both
those which are not considered as coal, and also the different species
of that mineral body.
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