, 1872-11-07
COAL.
Its 0riEiux

From the CosnAtz Nagaz1ne
A mistaken Impression is somewhat N1oely
prevalent that, in the coa}-falds, We have tho
remains Of ancient forests-in other words, It u
supposed that wherever there Was forest IN
primaval times there now exists coa1-feld OF
greater or less extent. In connection with tins
view, also, the opinion is entertained that 1he
forests now in existence will, in the process OF
time, and after due geological changes, become
the coal-beds OF future ages. But, although, as
ne shall presently see, the coalfelds are un~
donbtedly due to the vegetation Of former eras,
it is far from being the case that tie primeval
coal. Conditions Of peculiar, and to some ex-
tent exceptional, character were requisite for
the formation Of coa1-helds. Il we consider the
evidence given BY the coal-felds themselyes,
beds or seams Of coal form but a small por--
ton Of the thickness Of the great geological
group OF strata to which they for the most
part appertain. This group is called the
carboniferous, and not uncommonly the
Coal" but even where coal is most abundant
Thus it has been estimated, Sir Charles Lyeu
tells us, that in South Wales the thickness Of
the carboniferous strata amounts, in all, to be-
tween II 900 and u, 600 feet Tor more than two
miles,; but the various coal M seams do not &C.
aggregate 100 feet" or less than one-hundredth
paTt Of the whole. In North Lancashire the
carboniferous strata occupy depth OF more
than three miles. Here, no fewer than eighty
aeams Of coal have been counted (seVenty-
having been exposed by the action Of the sea) );
but these seams are nowhere moro than i've 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 por-
ton OF the time during which the carbon1ferous
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 noticed that under each coal seam
8 stratum Of ancient soil exlst8. IN which there
are commonly found the roots OF ancient trees,
while above the coal there is commonly layer
OF Bhale OF 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
transmitted into coal; the hollow OF the trunk,
decaying long before the trunk gave way Is rep
try to picture to ourselves the state Of things
which existed when such seam Of coal first be-
gan to be covered up by the next higher deposit,
re 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
vegetable layers 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
forest trees. Then the process Of deposition
began. This can only have happened when
some subsidence Of the soil had caused it to
be submerged to q greater Or less depth. We
can infer from the depth Of the strata overlying
the coal seams that this state Of submergence
continued in many cases for long period OF
time; and it is equally clear that the formation
OF the vegetable layers themselves must have
been process occupying. a considerable time,
since tall trees grew before the next submer-
gence took place. So soon as submergence was
complete, the tall trees :perished and began to
layer we're broken off and swept away BY the
sea. The forest itself, properly go called, Was
for the most part destroyed. It was the decay
ing refuse Of the forest, intermi1ed with the
lower growths, which formed the coal seam az
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
Yegetable matter, into coal.