When bituminous or lignitic coal, or even peat is subjected to a
sufficient degree of heat it is converted into hard coal and sometimes
into graphite. From this source some conclude that anthracite and
all hard coals are metamorphosed beds of soft carbon. But how about
the vast beds in aqueous crusts hundreds of miles from any igneous
agencies? All anthracite coal changed from bituminous coal will contain
a greater per cent. of ash than the coal from which it is derived. If
it does not it is evidence that it never was bituminous coal.
Let us suppose a heavy fall of Annular carbon in the north Atlantic
ocean, and that the Appalachian mountains were again under the
sea. The carbon carried by the ocean currents southward would fall
to the sea bottom in the more quiet waters. The heavy or anthracite
dust would reach the bottom in deep waters where the lighter forms
would not. Before the Appalachian upheaval, the eastern base of the
system was farther out in the sea, and was in deeper waters than the
western. The constitution of the coal itself, the condition of the sea
bottom (sloping from the coast to the deep sea) point harmoniously
to the annular origin of the carbon beds. The bituminous dust not
being able to directly settle with the anthracite remained longer in
suspension which accounts for its greater amount of ash. The farther
south it floated, the more impure it became. The heaviest beds of
anthracite will be found in the northern part of the great plateau, and
principally in British America if the Vailan theory is true.
Fossil plants in coal are generally mineralized charcoal, and are
difficult of combination. If the bed was composed of vegetable
production the same difficulty would certainly characterize the mass.
Hence the plant is simply a foreign body in a bed of mineral carbon.
Coal seams have become so hard as to be planed off by eroding forces
directly after being laid down, or before heavy beds had accumulated
over them. Thus they could not have been formed by vegetable peat.