THE ORIGIN OF COAL
“Coal is a fuel of inestimable value. By the heat which it develops in
burning it gives movement to divers machines. It makes the locomotive
move over the iron rails and the steamship traverse the ocean. With its
aid metals are worked, fabrics woven, pottery is baked, glassware
manufactured, newspapers and books are printed, tools are shaped, and
all sorts of instruments necessary to our daily activities are
produced. The arts and crafts have no more powerful auxiliary. If we
had to substitute the heat of wood for that of coal, our forests would
prove insufficient.
“What, then, is the origin of this combustible, which feeds an immense
industry and is the source of incalculable riches? Ordinarily a piece
of coal has no great interest for the eye. It is black, lustrous,
formless, friable, without any definite character to afford us
instruction. One can learn more from the fragments of refuse rejected
by the miner as too poor in carbon, fragments in which the
predominating element is a kind of dark stone that splits in sheets. In
these a surprise is lurking that will tell us the secret of coal.
“These laminate blocks, stone rather than coal, show us, on the slabs
that have just been separated by the blow of the hammer, various
wonderful designs in which we recognize without hesitation the imprint
or mold of some form of vegetation. There is no mistake about it; a
plant has left its remains there; we behold in very truth the leaf with
its subdivisions and its veins. It is all there, even to the minutest
detail. It is really the leaf minus the green color, for which is
substituted the black of the coal. We should not obtain a more exact
representation if we ourselves took the imprint of some sufficiently
firm leaf on a soft plaque of clay.
“Pending the time when some lucky chance shall bring you into the
neighborhood of a coal mine where you can obtain a laminate block that
you can split into sheets and thus discover for yourselves the
vegetable imprints there concealed, here is a picture that will show
you what these curious markings look like.
“What do you think of it? Have we not here what seems to be actual
leaves, and very elegant ones too? They are spread out with a care that
would appear to indicate the work of a painstaking human hand. Yes,
these are real leaves, but turned to carbon and firmly incrusted in
their bed of black rock.
“Similar imprints are found in great abundance in all coal mines.
Certain coal-deposits, several meters thick, are composed entirely of
them, the smallest chip that one splits off bearing on each face the
markings of foliage. The whole is nothing but an accumulation of leaves
and broken tree-trunks. An entire forest, heaped up in one pile, would
not present an equal mass. Thus it is demonstrated that in coal are
preserved the remains of ancient vegetation.
“During great floods the rivers of former ages swept away in enormous
masses the trees they had uprooted along the banks, together with the
foliage washed into the current by the heavy rains; then all this
refuse was deposited in the mud at the river’s mouth, or in some lake
or bay. Thus were amassed here and there, under the water, during a
long series of centuries, the remains of primitive forests.
“Fine clay became packed about these masses, molding itself with
delicate accuracy around even the smallest leaf; the weight of the
superimposed mud crushed the softened tree-trunks; a gradual decay
converted the whole into charcoal; and finally the ligneous mass became
a layer of coal. Later the waters changed their bed, driven elsewhere
by upheavals in the surface of the earth, and the previously inundated
bottom-lands became solid ground in which to-day we find coal under
massive strata of rock.
“Is it possible to distinguish the forms of plant-life whence has come
our coal? Yes, it is possible, so well preserved are the details of
that life in the products of our mines. Now an examination of the
imprints left to us in the laminæ or leaves of our stone book shows us
that the plant-life of those remote ages in which the coal was
accumulated bore not the least resemblance to that of our present
forests. And this difference was to be expected. The animal life has
changed; why, then, should the plant-life have remained unaltered?”
“Didn’t they have trees then like ours?” asked Jules.
“No,” replied his uncle; “we do not find in our coal mines any signs of
the existence of trees resembling those of our day. Nowhere in the
world, in fact, are there now to be seen any such forms of plant-life
as flourished so abundantly in those remote ages; or if any still exist
that are at all analogous, they must be sought in the islands of the
tropical seas. No vegetable growth of that coal epoch, whether tree or
bush or simple cluster of leaves, bore flowers. The splendors of the
corolla were not to appear until a later period.
“For the most part there were only tall stems or stalks, without
branches, of equal size from top to bottom, and furrowed with channels
or dotted with large points arranged in spiral lines. At the top a tuft
of enormous leaves balanced itself, the under surface of each leaf
bearing elongated or rounded swellings containing a fine brown dust,
each grain of which was a seed for the propagation of the plant.
“Plants that thus bear their seeds, or spores, in powdery masses on the
under side of the leaves are called ferns. A number of species flourish
in our part of the world. They are unpretentious plants, fond of shade
and coolness. Old damp walls, rocks that drip water drop by drop, the
darkest corners of our woods—these are the customary haunts of the
fern.
“A short underground stock and a sparse cluster of leaves, very
elegantly shaped, it is true, constitute our native ferns. Those of the
coal epoch were of a different pattern. Some of them displayed at the
top of a stem as tall as our poplars a cluster of leaves five or six
meters in length. They are called tree-ferns, and they contributed the
greater part of the coal-forming material.
“The accompanying illustration will give you an idea of what the
vegetation of that period must have looked like. What strange trees!
How different from our oaks and maples and hemlocks! The soil is a
liquid mud in which lie and rot the tree-trunks prostrated by the
weight of years; the air is sultry, moist, heavy, strongly impregnated
with a moldy smell; and the density of the foliage barely admits a few
sunbeams to flicker over the surface of the stagnant pools.
“Everywhere profound silence. No song of bird bursts forth from the
foliage of those tall fern-trees, for the bird is not yet in existence.
No foot of quadruped treads the ground, for the quadruped with its coat
of fur will not come until much later. Some lizards lurking in the
rock-fissures, some large dragon-flies at the water’s edge, some odious
scorpions under the heaps of dead leaves—that is all the animal-life to
be found in the forests that gave us our coal.”