New national era. [volume] (Washington, D.C.) 1870-1874, 1872-12-26
s9ai-s., Origin.

y mistaken impression is somewhat widel,
prevalent that, in the coal-feIds, We have the
remains of ancient fOrests-in other words. i
is supposed that wherever there was forest
in primeval times there now exists coal-felC
of greater or less extent. In connection
with this view, also, the opinion is enter
tanned that the forests now in existence will,
in the process of time, and after due geOlogi-
cal changes, become the coal-beds 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 be-
came converted in general way into coal
! Conditions OF peculiar, and to some extent
! exceptional, character were requisite for the
| foundation Of cOal-leds. five consider the
evidence given by the coal-fields themselves.
we shall see what these conditions were.
The beds or seams of coal form but small
portion of the thickness Of the great geologi-
cal group Of strata to which they for the most
part appertain. This group is called the car
DonlierouS, and not uncOmmonly " the Coal;'
but even where coal is most abundant, il
forms only minute part of the whole mass.
Thus 1t has been estimated, Sir Charles Lyell
tells us, that in South Wales the thickness of
the carbonlterous strata amounts, in all, to
between ii 900 and II, 900 feet, Cor more than
not" according to Professor Phillips, sex
coed in the aggregate 100 feet" or less than
one-hUndredth part Of the whole. In North
Lancashire the carbonterous strata occupy
depth OF more than three miles. Here. no
lever than eighty seams Of coal have been
counted, (seventy-one having been exposed
by the action of the sea ) but these seams
are nowhere more than five feet in thickness, |
ana many are but few inches thick. Thus,
il IS evident that the formation Of coal can |
have been in progress but a short portion OF |
the time during which the carbonterous Sc.
rlcs OF strata was in process Of deposition. |
Throughout by far the greater portion Of that !
time other minerals are 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 an
Gent trees, while above the coal there is
commonly 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 converted
INTO coal. The bark remains, but is trans
united into coal; the hollow of the trunk, de-
caylng long before the trunk gave wav, is
represented by cast in sandstone. Thus.
II we try to picture to ourselves the state of
things which existed when such a seam of
coal Lrst began to be covered up by the next
higher deposit, we see that there must have
peen trees standing erect above a LAYER of
vegetable matter, the roots of the trees being
in the soil which forms the deposit
next below the coal. The vegetable LAYERS
may probably have been two or three times
rs thick as the resulting coal seam, and were
by pressure TO their present thick
ness; but such layers cannot at anv time !
nave reached the branches of forest trees.
Then the process of deposition began. This
can only have happened when some subsi-
ience OF the soil had caused it to be sub.
merged to greater or less depth. We can
n'er from the depth Of the strata overlvino
The coal seams that this state of submerrence
continued in many cases for long period Of {
lime; and it is equally clear that the forma- !
lion OF the vegetable layers themselves must
nave been process occupying a consider
able 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 above the vegetable layer were bro
zen Off and swept away by the sea. The
orest itself, probably so called, was for the
most part destroyed. 1t was the decaying
'etuse of the forest, intermixed with the low
er grOwths, which formed the coal seam as it
low exists. Among these were the lower
parts of the trunks Of the ancient forest trees.
These became converted, like the rest Of the
matter, into coal.-COrnhiU Maga-
zine.