The Opelousas journal. [volume] (Opelousas, La.) 1868-1878, 1872-12-07
Origin of Coal

"A mistaken impression is somewhat
widely prevalent that, i'll coal-feIds, VIC
have the remains of ancient foPests-in
other words, it is supposed that Whcr-
ever there was q forest i'll primeval
times there now exists a coal-tiGld OF
greater or less extent. In connection
with this view, also, the opinion is ell
tertained that the forests now in eXis-
tence will, in the process of time, and
after due geological changes, become
the cOal-beds of future ages. But al
though, as we shall presently see, the
cOal-tields are undoubtedly due to the
vegetation OF former eraS, it is far from
being the case that the primeval for
ests became converted in Il general
way into coal. Conditions of a pecu-
liar, and to some extent exceptional.
character were requisite for the fOrma-
ton Of cOal-tields. If We consider the
evidence given by the cOal-fields them
selves, we shall see what these cOndi-
tons were. The beds or seams of coal
form but a small portion of the thick
ness Of the great geological group of
strata to which they for the most part
appertain. This group is called the
CarbOnlferOus, and not uncOmm0nlv
the COal;' but even where coal is most
abundant, it forms only a minute part
of the whole mass. Thus it has been
estimated, Sir Charles Lyell tells us,
that i'll South Wales the thickness of
the carbOniferous strata amounts in all,
to between 11,O0O and $4,000 feet (OT
more than two miles); but the various
c0ai,seams do not according to Prof.
Phillips, exceed in the aggregate 1870
feet" or less than one-hundredtR part of
the whole. la North Lancashire the
carbOniferOus strata occupy a deDth of
more than three and Il half miles. with
the same relative disprOpOrtiOn between
the thickness OF the cOal-seams and that
OF Incomplete series of strata. Again,
i'll Nova Scotia, the cOal-bearing strata
attain Il thickness of more than three
miles. Here, no fewer than eighty
seams OF coal have been counted (sev-
enty-One having been exposed by the
action OF the sea-; but these seams are
nowhere more than five feet in thick
ness, and many are but a few inches
thick. Thus, it is evident that the for
nation of coal can have been in pro-
gress but q short portion Of the time
during which the carbOnifcrOus series
of strata was in process of deposition.
Throughout by far,the greater portion
OF that time other minerals were being
deposited. 1t is next to be noticed that
under each coal seam a stratum of an
cient soil exists, in which there are
commonly found the roots of ancient
trees, while above the coal there is COM
monty n layer of shale OF sandstone, in
which not unfreGmently the trunks of
those trees are found either fallen OF
still i'll their original position, and only
partly converted into coal. The bark
remains, but is transmitted into coal
the hollow of the trunk, decaying long
before the trunk gave way, is represent
ed by a cast i'll sandstone. Thus, if we
try to picture to ourselves the state of
things which existed when such a seam
of coal first began to be covered I'D by
the next higher deposit, we see that
there must have been trees standing
erect above a layer of vegetable matter,
the roots of the trees being imbedded
in the soil which forms the deposit next
below the coal. The vegetable LAYERS
probably have been two or three times
as thick as the resulting coal seam,
and were reduced by pressure to their
present thickness but such layers can
not at any time have reached to the
branches of the forest trees. Then the
process of deposition began. This can
only have happened when some sub
sidence of the soil had caused it to be
submerged to Il greater or less depth. We
can infer from the depth of the strata
OVERLAPPING the coal seams that this
state of submergence continued in
many cases for a long period Of time ;
and it is equally clear that the forma-
ton of the vegetable layers themselves
must have been q process occupying
a considerable time, since tall trees
grew before the next submergence took
place. So soon as the submergence
was complete, the tall trees persisted
and began to decay. The stout trunks
above the vegetable layer were broken
off and swept away by the sea- The
forest itself, properly so-called, was for
the most part thus destroyed. 1t was
the decaying refuse of the forest, inter
mixed with the lOwlier grOwths, which
formed the coal seam as it now exists.
Among these we're the lower parts of
the trunks of the ancient forest trees.
These became converted, like the rest
OF the vegetable matter, into coal.
TTha NOTDhin