Once a Week (magazine)/Series 1/Volume 5/What is coal?

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WHAT IS COAL?

 

 

One of the most widely disputed questions of the present day, yet one on which there are perhaps more points of agreement than on almost any other, is that which has lately been so ardently contested—What is coal? It might appear, at first sight, that there could be no difficulty in answering this question, for who is there who does not suppose that he knows coal when he sees it? “Where ignorance is bliss, ’twere folly to be wise,” and but for a want of agreement among philosophers, we might have been content to believe that coal is coal.

In the year 1853, a remarkable trial took place in Edinburgh, which it might have been expected would have set at rest the question—what is coal? Not so; for although the trial lasted for six days, it opened wider than ever the portals of difference, and led to a succession of law-suits, each more involved than the last, and each bringing into the arena more numerous disputants and less prospect of agreement.

In the county of Linlithgow, and within a few miles of Edinburgh, there is a property of ancient tenure, celebrated for its coal and mineral formations, called Tarbanehill, and, in the year 1850, the owner of this property entered into a lease with certain coalmasters in the neighbourhood, in which it was conditioned that such lease was to comprehend the whole of the coal, ironstone, iron ore, limestone, and fire-clay therein found, but was not to include copper or any other minerals than those specified; and the tenants were to be allowed the first year of the lease without the payment of fixed rent, in order to enable them to make a search for other minerals besides those to which they were entitled by the terms of the lease, with a view to working them, if discovered, on other terms. Time wore on; and in 1852, two years from the date of the lease, circumstances came to the knowledge of the proprietor, from which he gathered that the lessees were turning out a valuable substance, not comprehended by the terms of the lease, neither coal nor any of the other minerals therein specified; and after satisfying himself upon the point, the owner of the property intimated to the tenants that the working of this substance must cease, while the tenants, taking a different view, maintained that they were working a gas-coal, to which they were entitled by the terms of the agreement.

Thus a controversy arose, and in order to aim at a decision of the question, an action was brought by the proprietor of the lands at Tarbanehill against the tenants, who were said to have infringed the terms of the lease by carrying away a substance that was not coal, but some other valuable mineral.

With a view to obtaining a conclusion which should be based on scientific data, Europe was searched for men of mark in the scientific world. Men who had arrived at the highest eminence in natural philosophy—men who had devoted themselves to the study of physical science—men who had made geology their leading study—men whose attention to microscopic botany peculiarly fitted them for forming an opinion—men who arrived at their conclusions by means of the study of mineralogy and chemistry—and, lastly, men who had passed their whole time in mines or mining pursuits were summoned to declare their views upon this vexed question.

Yet was it in no degree set at rest. After six days of debate, the philosophers, the geologists, the microscopists, the histologists, the mineralogists, the chemists, the miners, and the managers have, on the one side, such strong testimony that the substance was not coal, that the matter would have seemed clouded by no doubt, had not a similar array of evidence on the other side unhesitatingly brought arguments to show that it was coal, thus rendering arbitration on the subject more difficult and more remote than ever.

In order to understand how such contradictory arguments could be adduced on this celebrated trial, we must endeavour to have a general conception of what is intended by the term coal.

Looking back to that remote and indefined period “dateless as eternity,” and described by Coleridge as a state rather than a time, we recede into those extinct creations of a strange order, which constitute the penetralia of the carboniferous forest, and enter the period of the gigantic and magnificent flora of the coal measures. There, in that ancient scenery, with its amazing development of vegetation, unique in the history of creation, forms arose amid the steaming vapours of the time in rich and luxuriant grandeur. Amongst forests of arboraceous ferns, tall as trees, sprung up huge club masses, thicker than the body of a man; and thickets of Equisetaceæ or horse-tail, of prodigious growth, covered the marshes. There flourished the Vlodendron with its strips of cones adorning in vertical rows its carved trunks, its stems covered with leaf-like carvings, passing in elegance the minutest tracery of which we have any conception. There grew the Sigillaria, remarkable for their beautifully sculptured and tattooed stems, varying in pattern according to their species, and longitudinally lined with rows of leaves bristling from the stems and larger boughs, while their roots or stigmaria were fretted over and ornamented with eyelet holes curiously connected by delicately waved lines. There also gigantic Cacti, of intertropical growth, varied the landscape, and there too were Palms and Canes. Last and not least were the true forest trees of that era—the Pines and the noble Araucarians, the latter attaining a height of a hundred and fifty feet—three times that of our own forest trees. All these were loaded with cones; on all, cones were the only productions corresponding to fruit—fruit unfit and vegetation unadapted for food; and as in that age there were no herbivorous animals, there needed no provision in these primeval forests for such a race.

Yet the period of this flora was not less remarkable for its fauna; but it was an age of creeping things. There were reptiles and reptile fishes, which attained an enormous size, with defensive weapons of amazing strength, and some of them covered with enamelled scales of exquisite polish; there were sharks armed with razor-like teeth, with spines and with barbed stings; there were dragon-flies, snouted beetles and scorpions.

But—what is coal?

On the spot where the vast vegetation of the inconceivably remote carboniferous era flourished and decayed, we now find our beds of coal; to a depth of 10,000 feet, or nearly two miles, the coal beds or coal measures are in some places found to penetrate. Alternate seams of coal, of shale, of ironstone, of clay, and of rock, succeed each other through this great depth, in layers varying in thickness from a few inches to as many feet. For countless ages forests had their allotted growth, then a sudden submergence took place, and as the sea rushed in, a new feature in the landscape presented itself. On the then entombed vegetation, ridges of coral arose, forests of encrinites overlaid the forests of conifers, and produced in their turn beds of limestone, which again, deserted by the sea in its appointed time, afforded soil enough for trees whose rootlets required but little nourishment, and which flourished upon this new platform. These were again submerged when the sea rushed in, and corals and encrinites again set to work. How often these vast operations succeeded each other, and during what prolonged periods, there is no means of judging, except from the extended time which such growths must require. The world was old even then, and long anterior to these changes, unreckoned ages had gone by, producing formations of earlier date and longer process.

Thus we are brought to the close of the era denominated carboniferous—a period of gigantic vegetable growth, a period of ferns and conifers, a period of reptiles and fishes, a period having, like that of all organic existences, recorded and unrecorded, a beginning and an end; a beginning how remote! an end—how distant! Myriads of ages must have elapsed ere these vestiges of creation could have formed—by their own successive growth, by their subsequent mergence, by the formation above them of beds of coral, beds of limestone, and beds of shale, and again by a later and fresher vegetation—that solid and enduring mass of fuel, which yet may last for ages to come. That our coal was formed from these vast accessions of cryptogams, conifers, and sigillaria, is now beyond a doubt; for intertwined and interlaced with the fabric of the coal we find the plants themselves, crushed and altered it is true, but still retaining a part of their form and beauty. It is a matter of history, recorded by the botanist, microscope in hand, that in some coal all is vegetable structure; and though it is beyond human power to effect the transition from vegetable to coal, yet is it not difficult to comprehend the change which has taken place.

What is coal in its general signification composed of? Carbon, hydrogen, oxygen, and a small proportion of saline ingredients. What is a piece of wood, or a pine, or a fern composed of? Carbon, hydrogen, oxygen, with water, and a small proportion of saline ingredients.

Thus, the transition from vegetable to coal appears to consist principally in the loss, in the former, of the water or juices which constitute the sap of the plant, and which when no longer living it requires no more. Borne down by the flood, buried under the coral reef, it slumbers through ages and ages under the continually increasing pressure, till its juices being exhausted, its membranes are united in one solid mass, and the gradual process of eremacausis has connected foliage, trunk, and roots, into one homogeneous body, undistinguishable to an ordinary observer from its brother shale, found both above and beneath it in the mine. The point at issue between the scientific arbiters of this question raises our interest and excites our curiosity to know more upon a subject so fraught with mysterious grandeur; and when the distinction between our shales and coals, and other formations of the carboniferous era are more clearly defined, there will still be eager inquiries with each succeeding generation: What is coal?