“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, [[337]]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.
Fern Imprints from the Coal Epoch
“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 [[338]]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 [[339]]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?”