Coal

“ Formation of Coal—All coals are of vegetable origin and are the remains of prehistoric forests. Destructive distillation due to great pressures and temperatures, has resolved the organic matter into its invariable ultimate constituents, carbon, hydrogen, oxygen and other substances, in varying proportions. The factors of time, depth of beds, disturbance of beds and the intrusion of mineral matter resulting from such disturbances have produced the variation in the degree of evolution from vegetable fiber to hard coal. ”

“ Had I been writing a few years ago, I might have referred to the mode of formation of coal as one of the things most surely settled and understood. The labours of many eminent geologists, microscopists and chemists in the old and the new worlds had shown that coal nearly always rests upon old soil-surfaces penetrated with roots, and that coal beds have in their roofs erect trees, the remains of the last forests that grew upon them. ”

“ COAL, a black, opaque, inflammable substance, generally hard and compact, though laminated and stratified in beds between layers forming the crust of our earth. Coal has become one of the essential elements of modern civilization; in fact, the progress of the civilization of a country is now recorded by the amount of coal obtainable and employed by the inhabitants in a given time.—Mineral coal is a compound especially of carbon or of decomposed woody matter, with inflammable substances and hydrogen and oxygen gases. ”

“ Thus all this abundant wealth of money and of vivid life is Nature’s investment in club-mosses and the like so long ago. But what becomes of the coal which is burnt in yielding the interest? Heat comes out of it, light comes out of it, and if we could gather together all that goes up the chimney and all that remains in the grate of a thoroughly-burnt coal fire, we should find ourselves in possession of a quantity of carbonic acid, water, ammonia, and mineral matters, exactly equal in weight to the coal. ”

“ But the coal, which is certainly more useful than beautiful at present, has had a wonderful past. Besides the fossil-animals which are dug out of the earth's crust, there are also fossil-trees and ferns, and it is of them that coal, which seems only like a black stone, is made. I have read that in a part of England where there are now great coal mines, for a long time no one knew the worth of coal except some old women, who said they could make their fires burn beautifully by putting those black bits of stone upon them. ”

“ The coal is like the finest kinds shipped at Newcastle, and when analysed yields the same proportions of carbon and hydrogen, a fact worthy of notice when we consider that this fuel has been derived from an assemblage of plants very distinct specifically, and in part generically, from those which have contributed to the formation of the ancient or paleozoic coal. ”

“ Thus the final condition for the formation of coal was met, the exclusion of atmospheric air from this mass of decaying vegetation was complete, and under the water of the ocean, under the sand and silt of the shore, under the new deposits of succeeding ages, the transformation went on, the wood of the Carboniferous era became the coal of to-day, while above and below it the sand and clay were hardened into rock and shale. ”

“ The leaves are cell-villages which perform their daily tasks in the air and the light. Their principal business is to obtain coal, which is the chief constituent of the vegetable body. Our atmosphere is an enormous coal-mine, many miles in thickness, that can not be exhausted in thousands of thousands of years. The coal, indeed, is not found pure in the air, any more than the metal in the ore, but is in combination with oxygen as a transparent gas, carbonic acid, and a peculiar art is required to separate it. ”

“ But, if there are sermons in stones, why not in coal? The black thing, that we would rather not handle when we have any proper regard for cleanliness, becomes an object of interest when we find it exerting energy in the engine-furnace or shedding warmth and radiance around our household hearth. It becomes an object of yet greater interest when we come to learn its wonderful history; for every common bit of coal that we are accustomed to see has a history with which is wrapped up the story of one of the most interesting and critical periods in all geological time. ”

“ The chemical changes which have taken place in the beds of vegetation of the carboniferous epoch, and which have transformed it into coal, are even now but imperfectly understood. All we know is that, under certain circumstances, one kind of coal is formed, whilst under other conditions, other kinds have resulted; whilst in some cases the processes have resulted in the preparation of large quantities of mineral oils, such as naphtha and petroleum. ”

“ But of course coal is not made up wholly and only of leaves. The branches of trees, twigs of all sizes, and sometimes whole trunks of trees are found, the last often remaining in their upright position, and piercing the strata which have been formed above them. At other times they lie horizontally on the bed of coal, having been thrown down previously to the formation of the shale or sandstone, which now rests upon them. They are often petrified into solid sandstone themselves, whilst leaving a rind of coal where formerly was the bark. ”

“ Evaporation by the sun was at one time the sole means of obtaining salt from seawater; now coal is used to boil the salt pans and to purify the brine from the salt-mines in the triassic strata of Cheshire. The extent to which gas is used for illuminating purposes reminds us of another important product obtained from coal. Paraffin oil and petroleum we obtain from coal, whilst candles, oils, dyes, lubricants, and many other useful articles go to attest the importance of the underground stores of that mineral which has well and deservedly been termed the "black diamond." ”

“ Coal, in Southington, Connecticut. Beds of slate are found more or less bituminous; and, at the bottom of some of the wells, the slate begins to exhibit thin veins of coal, distributed in great numbers through the substance of the slate, which is the shale of the miners. The coal is from the thickness of a knife-blade to that of a finger; it is highly bituminous, and burns with great freedom. Even the entire masses of the stone burn brilliantly, when ignited on a common fire; and, after exhaustion of the coally matter, leave the slate of a grayish colour. ”

“ Where thirty or forty seams of coal have been found one below another, we have evidence of land and water thus changing places many times.
When vegetable matter is excluded from air and under great pressure, it decomposes slowly, parting with carbonic acid gas; and is first changed into lignite or brown coal, and then into bituminous coal, or the soft coal that burns with smoke and flame. I have been in a coal-mine where the carbonic acid gas, pouring from a crevice in the coal, put out a lighted candle. ”

“ The beds of coal differ in number and thickness in different areas, but they seldom or never exceed one-fiftieth part of the total bulk of the formation in thickness. The characters of the coal itself, and the way in which the coal-beds were deposited, will be briefly alluded to in speaking of the vegetable life of the period. In Britain, and in the Old World generally, the Coal-measures are composed partly of genuine terrestrial deposits—such as the coal—and partly of sediments accumulated in the fresh or brackish waters of vast lagoons, estuaries, and marshes. ”

“ A long interment followed, during which a course of Chemical changes, and new combinations of their vegetable elements, have converted them to the mineral condition of Coal. By the elevating force of subterranean Fires, these beds of Coal have been uplifted from beneath the waters, to a new position in the hills and mountains, where they are accessible to the industry of man. From this fourth stage in its adventures, our Coal has again been moved by the labours of the miner, assisted by the Arts and Sciences, that have co-operated to produce the Steam Engine and the Safety Lamp. ”

“ Wood, peat, brown coal, jet, and true coal, are chemically alike, differing only in their amount of oxygen, due to the difference of compression to which they were subjected. The sun gave his heat and light to the forests now turned into coal, and when we burn it ages afterwards, we revive some of the heat and light so long untouched. ”

“ We have now examined those strata which may be considered as either proper mineral coal, or as only a bituminous schistus; we are now to class along with these another species of this kind of matter, which has had a similar origin, although it may assume a different character.
According to the common observations of mankind, the eminent quality by which coal is to be distinguished, is the burning of that substance, or its capacity for making a fire. ”

“ COAL, PETROLEUM, AND NATURAL GAS
Coal. Most valuable of all geological products is coal. Although it is not, strictly speaking, a mineral, both because of its organic origin and lack of definite chemical composition, coal is generally classed among our mineral resources. Some idea of the national importance of coal in the United States may be gained when we realize that the energy derived from a single year’s output is equivalent to that of hundreds of millions of men working full time through the year. The uses of coal are too well known to need mention here. ”

“ And he tells us that wood can become lignite, or wood-coal, by parting with its oxygen, in the shape of carbonic acid gas, or choke-damp; and then common or bituminous coal, by parting with its hydrogen, chiefly in the form of carburetted hydrogen—the gas with which we light our streets. That is about as much as the unscientific reader need know. But it is a fresh corroboration of the theory that coal has been once vegetable fibre, for it shows how vegetable fibre can, by the laws of nature, become coal. ”

“ When we add to this that the coal itself is, chemically, nearly wholly composed of carbon, and that its microscopic structure shows it to be composed almost entirely of fragments of stems, leaves, bark, seeds, and vegetable débris derived from land-plants, we are readily enabled to understand how the coal was formed. The "under-clay" immediately beneath the coal-bed represents an old land-surface—sometimes, perhaps, the bottom of a swamp or marsh, covered with a luxuriant vegetation ”

“ The stems of plants do not lose their microscopic structure in all the ages it has taken to transform them to coal. A thin section of coal shows under a magnifier the structure of the stems of the coal-forming plants. Moreover, the veins of coal preserve above or below them, in shales that were once deposits of mud, the branching trunks of trees, perfectly fossilized. There are no better proofs of the vegetable origin of coal than the lumps themselves. But they are plain to the naked eye, while the coal tells its story to the man with the microscope. ”

“ Our abundant store of coal and its application to industrial purposes have been among the largest causes of our wealth and progress. The value of coal for those purposes depends essentially upon the fact that it is combustible and evolves a large amount of beat in burning, and that this heat can be set free at any time and be readily converted into mechanical, chemical, electrical, and other forms of power. ”

“ Some conception may be had of the enormous vegetable deposits of the Carboniferous era by recalling the fact that the resultant coal in each seam is only from one ninth to one sixteenth in bulk of the woody fibre from which it has been derived, the loss being mainly in oxygen and hydrogen. ”

“ It must not be thought that in this huge area the coal is all uniformly good. It varies greatly in quality, and in some districts it occurs in such thin seams as to be worthless, except as fuel for consumption by the actual coal-getters. There are, too, areas of many square miles in extent, where there are now no coals at all, the formation having been denuded right down to the palaeozoic back-bone of the country. ”

“ Each of these three kinds of coal, besides the line distinct reticulation of the original vegetable texture, exhibits other cells, which are filled with a light wine-yellow-coloured matter, apparently of a bituminous nature, and which is so volatile as to be entirely expelled by heat, before any change is effected in the other constituents of the coal. ”

“ The deeper beds of coal are better than those formed in comparatively recent time and found lying nearer the surface. In many bogs a layer of embedded root fibres, called peat, is cut into bricks and dried for burning. Deeper than peat-beds lie the lignites, which are old beds of peat, on the way to become coal. Soft coal is older than lignite. ”

“ How many times was this question asked before Science could return an answer? This she can now do with confidence. Coal was once growing vegetable matter. On the surface of the shale, immediately above the coal, you will find innumerable impressions of leaves and branches, as perfect as artist ever drew. But how could this vegetable matter ever accumulate in such masses as to make beds of coal of such vast extent, some not less than 30 feet thick? It would take 10 or 12 feet of green vegetable matter to make 1 foot of solid coal. ”

“ But many of these deposits were washed away during subsequent land elevations. In some parts of North America and Europe the coal-bearing strata are 18,000 feet in thickness.
The presence of roots of trees as they grew in the clay underlying the present coal beds demonstrates that coal was formed exactly where it is now found. Coal is the water-preserved and pressure-modified remains of the rank vegetation growing in the bogs and on the swamp shores of this faraway age. Coal layers often hold both gas and oil. ”