New national era. [volume] (Washington, D.C.) 1870-1874, 1872-10-31
Origin Of Coal.

n mistaken impression is somewhat widely
prevalent that, in the coal-fields, we have
the remains of ancient forests-in other
words, it is supposed that wherever there
was forest in primcval times, there now
exists coal-iield of greater or less extent.
In connection with this view, also, the opn-
ion is entertained that the forests now in ex-
lstence will, i'll the process of time, and after
due geological changes, become the cOal-beds
of future ages. But although, rs we shall
presently see, the coal-lields are undoubtedly
due to the vegetation of former cras, it is far
from being the case that the primeval forests
became converted in general way into coal.
Conditions of a peculiar, and to some extent
exceptional, character were requisite for the
formation of cOal-felds. If we consider the
evidence given by the coal-fields themselves,
we shall see what these conditions were
The beds or seams of coal form but n small
portion of the thickness of the great geo
logical group of strata to which they for the
most part appertain. This group is called
the carbonifcrous, and not uncommonly" the
Coal :" but even where coal is most abmd-
ant, it forms only n 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 ii 900 and l2,-
600 feet, Cor more than two miles y "but
the various coal seams do not" according to
Prof. Phillips, "excccd in the aggregate 100
feet" or less than One-hundreth part of the
whole. In North Lancashire the carbon
ferrous strata occupy a depth of more than
three and half miles, with the same rela-
tive dsproportion between the thickness of
the coal seams and that of the complete
series of strata. Again, in NOvia Scotia, the
coal-bcaring strata attain thickness gilmore
than three miles. Here, no fewer than
eighty seams of coal have been counted
(seventy-one having been exposed by the
action of the sea y but these seams are no.
where more than five 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 carboniferous series
of strata was in process of deposition,
Throughout by far the greater portion of
that time other minerals were being dcpOs-
tied. 1t is next to be noticed that under
each coal seam a stratum of ancient soil eX-
lists, in which there are commonly found the
roots of ancient trees while above the coal,
there is commonly n layer of shale or sand
stone, in which not unfrequently the trunks
of those trees are found either fallen or still
in 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 represented by cast in sandstone.
Thus, if we try to picture to ourselves the
state of things which existed when such 4
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. The veSe-
table layers may probably have been two or
| S.1- lRa,nrr
seam, and were reduced by pressure to their
present thickness but such layers cannot at
any time have reached to the branches of
the forest trees. Then the process of depo-
sition 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
everything the coal seams that this state of
submerUence. continued in many cases for 4
long period of time; and it is equally clear
| that the formation of the vegetable layers
| themselves must have been a process Occu-
| pync a considerable time, since tall trees
| grew before the next submergence took
place. So soon as submcrgcnce was COM
plete, the tall trees persisted and began to
| decay. The stout trunks above the vegeta-
| BILE 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 decayng refuse of the forest, inter
| mixed 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 con-
verted, like the rest of the vegetable matter,
into coal -Fbe CO1uHW,