The Arizona sentinel., 1885-10-31
READING FOR THE YOUNG.
THE FORMATION OF COAL.

Present Results-How the Question of
Time Is Determined.
According to the calculations of
prominent geologists, the stratum of
earth that in some places is two miles
and half thick, constituting the car
boniferous or coal age, was. deposited
twenty-nine million years ago. You
will wonder how such calculation can
be made. The result is arrived at by
finding out hoa0 the different layers are
deposited, and estimating the larger
ones by the smaller As an example,
the same agencies are at work now as
then Deposits ike those of the Dover
Cliffs, England are being formed at
the bottom of the ocean to-day; and by
noting the ages of time it takes TO raise
a given area an inch, by mean seven OF
the fast-growing coral. we can form
something of guess how long it would
take for two and a half miles of solid
covering to form.
During this time, as the name indi-
Gates, the great beds of coal in Penn
sylvania and other sections were
deposited, and as we sit by a spark
ling coal-fire we are, after all,
watching a wood one-the wood of
twenty-nine million years ago. If you
doubt this, grind piece of coal down
as thin as possible and place it under
a microscope, when the woody fiber
will be plainly seen.
Mineral coal is merely the element
of carbon mixed with other bituminous
substances. In the formation of BIZ
luminous coal there was a loss of three
fourths of wood and five-sixths in that
of anthracite. There was greater
loss by decomposition, and reduction
of bulk by pressure from above, and
from this it is assumed that it took
eight feet of leaves and twigs that
dropped from the trees and blew to-
gether. packed closely, to make one
foot of bituminous coal, and twelve
feet to make one of anthracite.
To make a bed of coal thirty feet
thick, like the one in Wilkesbarre, the
bed of vegetable matter that produced
it must nave been three hundred and
sixty feet thick. Imagine the time it
would take for leaves to drop and
accumulate in solid mass over great
area as high as the tallest church-spire!
Hence it is that seams or layers of pure
coal are rarely very thick. Often
times the layer is as thin as piece of
paper. but the average is about eight
feet. The Pittsburgh seam, at the place
of the same name, is just this thickness,
and can be seen on the high shores from
Is.H- q f-,
Virginia and Ohio, over an area Of two
'et and twenty-five by one hun
.-a. miles. aut even into Kentucky. il
r4Ha- a.a. 10 thickness. rs iu the Cum
'#-l 5 fs fourteen feet .Tick
- linz tive 90 Athens, o.. and
he Great kz- VIVA from two to
tuteo ioo..
Coal-beds form much quicker under
water, where the leaves were held in
place and retained their gaseous parts
which would be lost in the atmosphere.
The common peat-beds of to-day are
perhaps coal-beds of the future-at
least, they resemble in origin the old
plant-beds. Over One-tenth of ireland
is covered with peat-beds, some forty
feet deep. In Massachusetts, alone,
there are over 12O, 600, 900 cords of it.
Trees are often found buried in them,
and in Ireland 4 gigantic fossil elk is
found.
You may wonder where all the car
bon came from that seems to be the
prominent ingredient in coal. II is be-
lieved that in the coal age there was
much more carbon in the atmosphere
than at present, and during this time
it was stored away by the wonderful
plants that were so fitted for the pur-
pose. This, too, purified the air for
the birds and higher forms that came
later.
The curious mineral oil, petroleum,
was formed similarly to coal by the de-
composition of vegetable or animal re-
mains, either marine or terrestrial,
buried in mud, in time slowly changing
into oil, or some materials that pro-
duce it by distillation; but oil, unlike
the coal, is found in the layers of all
ages, from the lower Silurian wells of
Kentucky and Tennessee to the Terti-
airy wells of Southern California.
Like other strata, that of the coal
age only appears at the surface at GER
tain places-in fact, the total number
of square miles of all the productive
coal-fields in the United States is only
125, 900; in Scotland, 1000 square miles;
Ireland, 1850, 900, and in England, O.
250, 900 square miles. Then again, it
is not always represented by coal. 1t
contains stratified rocks of all kinds,
sometimes shales, sandstones, con-
glomerates. But how, you will ask,
were all these layers placed there? o.
Geology shows us that the age just
before the coal was one of submergence
that is, most of the land was under
water: but later, there was rising,
and great tracts of swamp-land ap-
peared In them grew trees and vege-
tation totally unlike those of to-day,
the ferns even being trees, and large
ones, too. The vegetation was Won
derfully profuse. Curious flowerless
plants called cryptograms were COM
mon "a sort of ground pine. A Lyco-
podia that lives now, four or five feet
high, in this wonderful time was sixty
or seventy feet high. One of the COM
monest trees was the Sigillaria, which
grew to a height of sixty or seventy
feet also, and then branched out with
long. narrow leaves, the trunk being
covered with curious scales. They are
frequently found in mines, and are eX-
tremely dangerous, as they hollow out,
become filled with sand and rock, and
when broken off below, shoot down
upon the miners. Their roots are often
found spreading through the coal in
every direction.