Year: 1872

A mistaken impression is somewhs,
widely prevalent that in the coal-felds We
have the remains of ancient forests-in
other words, it is supposed that wherever
there was forest in primeval times there
now exists coal-6eld of greater or less
extent. In connection with this, also, the
opinion is entertained that the forests now
in existence will, in the process of time,
and after due, geological changes, become
the coalbeds of future ages. But although,
as we shall presently see, the coal fields
are undoubtedly due to the vegetation Of
former eras, it is far from being the case
that the primeval forests became converted
in general way into coal.


Conditions of peculiar and to some
extent exceptional character were requis-
ite for the formation of coal-6elds. If we
consider the evidence given by the coal


fields themselves, we shall see what these
conditions we're. The beds or seams of
coal form but small portion of the thick
ness OF the great geological group of strata
to which they, for the most part, appertain.
The group is called the carboniferous, and
not uncommonly "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 in South Wales the thickness of
the carboniferous strata amounts, in all, to
between IL 900 and 10000 feet Cor more
than two miles) "but the various coal
seams do not, according to Professor Phil
lips, "exceed in the aggregate 120 feet" )"
or less than one hundredth part of the
whole. In North Lancashire the carbon
iferous strata occupy depth of more than
three and half miles, with the same rela-
tive dislroportion between the thickness Of
the caal.seams and that of the complete
series ofstrata.


Again, in Nova Scotia the coal-bearing
strata attain thickness of more than three
miles. Here no fewer than eighty seams
of coal have been counted (seventy- hav-
ing been exposed by the action of the sea-;
but these seams are nowhere more than live
feet in thickness, and many are but few
inches thick. Thus it is evident that the
formation of coal can have been in progress
but short portion Of the time during which
the carbonifeous series of strata were in
process of deposition. Throughout by far
the greater portion of that time other min
eral were being deposited. 1t is next to be
noticed that under each coal-seam stratum
of ancient soil exists, in which there are
commonly found the roots of ancient trees;
while above the coal there is commonly a
layer of shale or sandstone, in which not
unfrequently the trunks of those trees are
found. either fallen or still in their original
position, and only partly covered into
coal. The bark remains, but is transmitted
into coal the hollow of the trunk, decay
ing long before the trunk gave way, is rep
resented by cast in sandstone.


Thus, if We try to picture to ourselves
the state of things which existed when such
seam of coal first began to be covered up
by the next higher deposit, we see that
there must have been trees standing erect
above layer of vegetable matter, the roots
of the trees being imbedded in the soil
which forms the deposit next below the coal.
Two vegetable layers may probably have
Ueeu tWU VI tHISC tlueo do lulCh do IuC I6-
sultiug coal seam and were reduced by pres
ure to their present thickness; but such
layers cannot 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 subsistence Of
the soil had caused it to be submerged to
greater or less depth. We can infer from
the depth of the strata overlying the coal
seams that this state Of submergence con-
tinued in many cases for long period of
time and it is equally clear that the for
nation of the vegetable layers themselves
must have been process occupying con-
siderable time, since tall trees grew before
the next submergence took place. So soon
as submergence was complete, the tall trees
perished and began to decay. The stout
trunks about 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 de-
caying refuse of the forest, intermixed with
the lowlier growths, which formed the coal
seam as it now exists. Among these were
the lower parts of the trunks of the ancient
forest trees. These became converted, like
the rest Of the vegetable matter, into coal.
The Cornhill.