Lignite

“ You may find about the world—you may see even in England alone—every gradation between coal and growing forest. You may see the forest growing in its bed of vegetable mould; you may see the forest dead and converted into peat, with stems and roots in it; that, again, into sunken forests, like those to be seen below high-water mark on many coasts of this island. You find gradations between them and beds of lignite, or wood coal; then gradations between lignite and common or bituminous coal; and then gradations between common coal and culm, or anthracite, such as is found in South Wales. ”

“ Even the trap-rocks of the district enclose, in some instances, their masses of lignite, which present in their transverse sections, when cut by the lapidary, the net-like reticulations of the coniferæ. The fossil botanist, who devoted himself chiefly to the study of microscopic structure, would have to decide, from the facts of the case, not that trees were absent during the Carboniferous period, but that, in consequence of their having been present in amazing numbers, their remains had entered more palpably and extensively into the composition of coal than those of any other vegetable. ”

“ What are called the carbon minerals--peat, lignite, coal, graphite, asphalt, petroleum, etc.--are, properly speaking, not minerals at all, as they are organic substances, and have no definite chemical composition or crystalline forms. They are, in fact, chiefly the products or phases of a progressive and inevitable change in plant-tissue, which, like all organic matter, is an unstable compound and destined to decomposition. ”

“ Masses of vegetables buried beneath beds of tenacious clay, by which the escape of the gaseous elements set free by decomposition was prevented, must have been placed under the most favourable conditions for their conversion into lignite and coal. ”

“ These beds sometimes attain a thickness of above twenty yards, but in the environs of Paris they form beds of a few inches only, which alternate with clays and sands. We cannot doubt that lignites, like true coal, are the remains of the buried forests of an ancient world; in fact, the substance of the woods of our forests, often in a state perfectly recognisable, is frequently found in the lignite beds; and the studies of modern botanists have demonstrated, that the species of which the lignites [355] are formed, belong to a vegetation closely resembling that of Europe in the present day. ”

“ These lignites or modern coals are only peat beds which have been buried for a longer or shorter time under clay, sand, or solidified rock, and have progressed farther or less far on the road to coal. As with peats, so with lignites, we find that at different geological levels they exhibit different stages of this distillation--the Tertiary lignites being usually distinguished without difficulty by the presence of a larger quantity of combined water and oxygen, and a less quantity of carbon, than the Cretaceous coals, and these in turn differ in the same respects from the Triassic. ”

“ It is, however, a fact that some of the lignite clay-beds, and those of the coal-measures, too, are clean or without admixture of vegetable remains, even of rootlets. But when the peat is beginning its growth at the surface of a somewhat deep basin of water, whose bottom has been rendered impermeable by the deposit of clay (which always precedes the deposit of woody materials) , this surface-peat is often thick and compact before it is forced down and comes in contact with the clay; and, in that case, therefore, the clay is pure, or is not penetrated by roots or rootlets. ”

“ Very recent discoveries of better quality have been reported. Tertiary fibrous lignite, of light specific gravity, is found in great abundance all along the junction of the coast plain and black prairie regions. It is worked to a small extent, but has no commercial value. The most important coal area is the semi-bituminous lignite belt of the trans-Pecos and lower Rio Grande regions, which is the direct geographical continuation of
the late Cretaceous coals of New Mexico and Colorado. ”

“ By a continuation of the same processes the mass becomes still more dense and solid. As we pass from the top to the bottom of such an accumulation of peat, we find it becoming denser and denser, and at the bottom it is commonly of a hard consistence, brownish in colour, and with only slight traces of the original woody structure. Such material is called lignite. It contains a higher percentage of carbon than peat, but a lower percentage than coal, and is plainly a step in coal formation. But the process goes on, the hydrogen and oxygen loss continuing until there is finally produced true coal. ”

“ It appears from the researches of Liebig and other eminent chemists, that when wood and vegetable matter are buried in the earth, exposed to moisture, and partially or entirely excluded from the air, they decompose slowly and evolve carbonic acid gas, thus parting with a portion of their original oxygen. By this means, they become gradually converted into lignite or wood-coal, which contains a larger proportion of hydrogen than wood does. ”

“ The workings, which are very limited, had been carried out without any system, and much of the lignite had been lost in winning. The quality of the lignite is very satisfactory. It keeps well, and burns with a long flame. Owing to the exceptional conditions under which these deposits can be worked—the seams lying horizontally, and being entirely free from water or deleterious gases—no shafts are required, and the ventilation is a very simple matter. ”

“ The western features are, as a rule, broad, with shallow sag: here, according to some, [79] was deposited the Surtarbrand [80] or lignite, and, like the driftwood of Kerguelen Island, it escaped incineration by subsequent eruptions from causes analogous to the operation of charcoal burning. The northern firths are long and deeply indented, and the eastern are sharp and narrow, encased in walls of Palagonite, trap, and basalt. ”

“ But some deposits of peat are so recent that their beginning is positively remembered by old men, who have seen them grow to some thickness where as children they had seen only stagnant pools, or a forest, or a muddy swamp. All these peat deposits, like the beds of coal and of lignite, are found in connection with vegetable remains which are either dead and cover them entombed in the clay of their surface, or are still living and deposit and heap their woody matter upon them, thus constantly increasing their thickness. ”

“ It retains the woody forms of the vegetable growths which constitute it, and they are often but loosely adherent to one another. Peat may be merely a growth of the past five years, but is sometimes many thousand years old. Older than peat, and more caked and compressed, is lignite, or brown coal, which occurs on the Continent of Europe, also in South Devon and elsewhere, in geological strata newer than those which yield our black 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. ”

“ Flat, swampy coastal plains are believed to furnish the best conditions for thick accumulation of peat. There is good evidence that most of the deposits accumulate essentially in place, without appreciable transportation.
In time these surface accumulations of vegetable material may subside and be buried under clay, sand, or other rock materials. The processes of condensation begun in the peat bog are then carried further. They result in the second stage of coal formation, that of lignite or brown coal. ”

“ The peculiar mode of decay of the organic matter in such fine soils seems analogous to that by which vegetation has been turned into coal or lignite when so buried under detrital material as to greatly impede the access of the air. It is now easy to see why plains are likelier than mountain slopes to be treeless, it being towards the plains that the finer particles of the material which is abraded from the higher regions are being constantly carried. ”

“ In these constantly warm and damp atmospheric strata, saturated with p 219 carbonic acid, vegetation must have attained a degree of vital activity, and derived the superabundance of nutrition necessary to furnish materials for the formation of the beds of lignite (coal) constituting the inexhaustible means on which are based the physical power and prosperity of nations. Such masses are distributed in basins over certain parts of Europe, occurring in large quantities in the British Islands, in Belgium, in France, in the provinces of the Lower Rhine, and in Upper Silesia. ”

“ Of the other possible sources of supply, coal yields too little, and at the same time is considered too valuable to be utilized on a general scale; lignites are not yet opened for development on a sufficient scale ”

“ The lignites, which we find in the Miocene, as in the Eocene period, constitute, however, a combustible which is worked and utilised in many countries, especially in Germany, where it is made in many places to serve in place of coal. ”

“ But we have better evidence than this of the derivation of one from another of the groups of residual products which have been enumerated. In many localities, the coals and lignites of different ages have been exposed to local influences--such as the outbursts of trap-rock, or the metamorphism of mountain chains--which have hastened the distillation, and out of known earlier groups have produced the last. For example, trap outbursts have converted Tertiary lignites in Alaska into good bituminous coals ”

“ A clay soil, in which, in addition to the predominating alumina, there is a fair proportion of lime, may be regarded as the most fertile for all purposes; but we have few such in Britain, our clays being mostly of an obdurate texture, retentive of moisture, and requiring much cultivation, and containing, moreover, salts of iron in proportions and forms almost poisonous to plants. But there are profound resources in most clays, so that if it is difficult to tame them, it is also difficult to exhaust them. ”

“ Nearly all the rocks and minerals out of which fertile soils are formed,—which therefore contain those inorganic matters that are essential to vegetable growth,—though very slowly acted on by pure water, are decomposed and dissolved to a much greater extent by water, charged with carbonic acid gas.
It is by these solvents that the formation of soil from broken rocks is to a great extent due. Clay is invariably a result of their direct action upon rocks. The efficiency of the soil depends greatly upon their chemical influence. ”

“ The quantity used per acre depends largely on the nature of the soil. Stiff clays and sour marsh lands require a larger dressing than loams or well aerated soils. From three to six thousand pounds per acre are the quantities usually employed. When the lime is once thoroughly incorporated in the soil it is rapidly converted into carbonate, but while in the caustic state it may act vigorously in promoting the decay of organic matter and may prove injurious in promoting the decomposition of ammonium salts with attendant loss of nitrogen. ”

“ In many cases the farmer fears, as he does in the county of Durham, to bring up a single inch of the yellow clay that lies beneath his soil. In the first inch lodges, among other substances, the iron worn from his plough, which in some soils, and after a lapse of years, amounts to a considerable quantity. Till it is exposed to the air, this iron is hurtful to vegetation, and one of the benefits of a winter’s exposure of such subsoils to the air, is the effect produced upon the iron it contains. ”

“ Those parts which constitute the larger proportion of the soil, namely the clay, sand, and limy portions, are useful for purposes which have been named in the first part of this section, while the clay has an additional effect in the absorption of ammonia.
For this purpose, it is as effectual as charcoal, the gases escaping from manures, as well as those existing in the atmosphere, and in rain-water, being arrested by clay as well as charcoal. [T]
What particular condition of inorganic matter is requisite for fertility? ”

“ If a soil be shaken up with water and allowed to stand for a few minutes, it rapidly deposits a quantity of grains which are at once recognised as common sand; and if the water be then poured off into another vessel and allowed to stand for a longer time, a fine soft powder, having the properties and composition of common clay, is deposited, while the clear fluid retains the soluble matters. By a more careful treatment it is possible to distinguish and separate humus, and in soils lying on chalk or limestone, calcareous matter or carbonate of lime. ”

“ In all soils, except the oosur, fine trees grow, and good crops are produced under good tillage; but in the muteear, the outlay to produce them is the least. It is an error to suppose that a soil, even of pure sand, must be absolutely barren. Quartz-sand commonly contains some of the inorganic substances necessary to plants—silica, lime, potash, alumina, oxide of iron, magnesia, &c.—and they are rendered soluble, and fit for the use of plants by atmospheric air and water, impregnated with carbonic-acid gas, as all water is more or less. ”

“ The earthy or insoluble portion.—The earthy or insoluble portion of soils rarely constitutes less than 95 lbs. in a hundred of their whole weight. It consists chiefly of silica in the form of sand, of alumina in the form of clay, and of lime in the form of carbonate of lime. It is rarely free, [Pg 73] however, from one or two per cent. of oxide of iron; and where the soil is of a red colour, this oxide is present in a still larger quantity. A trace of magnesia also may be almost always detected, and a minute quantity of phosphate of lime. ”