Year: 1873

The origin OF CoAL.-A mistaken


impression Is somewhat widely prevalent
that. in the coal fields, We have the re
mains of ancient forests-in other words, it
is supposed that wherever there was for
est in primeval times, there now exists i
coal field of greater or less extent. La
connection vita THIS view, also, the opinion


is entertained tnat the forests now in ex-


stence will, in the process Of time. ani


after due geological changes, become the
coal beds OF future ayes But although,
as we shall presently see.the coal fields are
undoubtedly due to the vegetation Of for
mer eras, it is far from being the case that
the primevai forest became converted 10
general way into coal. Conditions OF
peculiar, and to some extent, exceptional


character, were requisite for the tormltlon
of coal fields. If we consider the ev deu:e


given by the coal fields themselves, We
shall see what these con ltions we're. Tae
beds or seems of coal form but small
portion of the thickness Of the great geo


logical group of strata to which they for


the most part aPpertain. The group is
called the carbOnlterous, AMI not uncOm
monty the coal : but even where Goa. is
abundant, it forms only minute part OF
the whole mass. Thus, it is estimated,
Sir Charles L.ell tells US, that in South


Wales the thickness of the carbonlerous
strata amounts, in all, to between eleven
thousand and twelve thousand feet, or
more than two miles; bat the various coal
seams do not, according to Prof Phillips,
exceed in the aggregate one hundred and
twenty feet. or less than one-hunlredth
part Of the whole To North Lancashire
the carbonierous strata occupy a depth OF
more than three and half miles, VITA the
same relative disprop0rtion in thickness of
the coal seams and that Of the complete
series of strata. Again, in Nova Scotia,
the coal bearing strata attain a thickness
Of more than three miles. uere, no fewer
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,
and many are but a few inches thick.
Thus it is evident that the formation of
co al can have been in progress but a short
portion of the time during which the car
| boniferous series of strata was in process
of deposition. Throughout by far the
greater portion of that time other minerals,
we're being deposited. 1t is next to be no
ticed that under each coal seam stratum
of ancient soil exists, in watch there are
commonly found the roots Of ancient trees ;
while above the coal there is CO nmonly a


laver of shale or sandstone, in which not
unfrequently the trunks of those trees are
found either fallen or in their original po-


sition and only partly converted into coal


The bark remains, but is Transmitted into
coal; the hollow of the trunl, decaying


long before the trunk gave way, is repre-
sented by cast in sandstone. Thus, il


we try to picture to ourselves the state OF
things which existed when such a seam Of
coal began to be covered up by the next


higher deposit, we see that there must


have been trees standing erect above lay
er of vegetable matter, the roots of them
being imbedded in the soil which forms the
deposit next the coal The vegetable


layer may 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. Tnen the


process of gradual deposition began. Tais


only can happen when some su5sidence o.


the soil had caused it to be submerged tC
or eater or less depth. We can infer
from the depth Of the strata overlying
the coal seams that this state of submer
gence continued in N my cases for a long
period of time; and it is equally cleal
that the formation Of the vegetable layer
themselves must have been process oc
|. cupy:ug considerable time, since tai
trees grew before the next snbmergenc'
took place. So soon as submergence wa


complete the trees perIshed and began tt


decay. The stout trunks above the veg
etable layer were broken off and swep
away by the sea. The forest itself, prop