Class 1 . —MINING AND MINERAL PRODUCTS.
[United
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AN ACCOUNT OF THE NATURE AND EXTENT OF THE VARIOUS DEPOSITS OF MINERAL FUEL
IN VARIOUS PARTS OF THE WORLD.
Accompanied by a Map, showing the extent and position of the principal Coal-fields of Europe and
By D. T. Ansted, M.A., F.R.S., &c., Prof. Geol., K.C.L.
1. General Account of Materials used for Fuel.
The chief supplies of valuable fuel are, and alwayshave been, derived immediately or distantly from thevegetable kingdom. Whether in the form of wood,peat, lignite, or coal of various kinds, the original sub-stance of all fuel has been found to have this origin, andthus it would seem that the power of vitality exerted inproducing woody fibre has been from time to time storedup, as it were, into vast reservoirs, where it might bepreserved safely and permanently for an indefinite pe-riod.
In warm climates, where the growth of vegetation isextremely rapid, and comparatively little fuel is needed:or in the early periods of civilization, before men con-gregate in large masses in towns, or are actively employedin manufacture, there is little need of more fuel than is sup-plied by the natural growth of forests; but under other cir-cumstances, where forests are gradually removed, andthe consumption of fuel at the same time increases, thereserved stores are greatly needed, and must ultimatelybe reckoned among the main sources of a country’swealth. The accumulations of mineral fuel in the Bri-tish islands may be ranked as one of those natural ad-vantages without which our country could not possiblyhave taken up and held for a long time the position sheoccupies among the nations of the earth; and thus, as oneof the great and principal sources of its mineral treasure,the coal deposits of England demand and deserve ourcareful attention. The relative supply of other countries,and the activity and energy displayed in taking advantageof the existence of mineral fuel, must also be worthy ofattention, as illustrating and explaining the condition ofmany manufactures, and the probable advance of theinhabitants of such districts in the refinements of civili-zation. Since the introduction of steam-power for allpurposes of machinery, the consumption of coal hasvery greatly increased, and at present it would be diffi-cult to set any limits to the use of so valuable a ma-terial.
The changes undergone by vegetable matter when bu-ried in the earth and accumulated in large quantities,and the length of time needed to produce any markedalteration, are subjects rather more interesting, it mayseem, to the chemist than to the practical man, wholooks only for fuel that he may employ economically.But inasmuch as the real condition of coal varies consi-derably, and different kinds are valuable for differentpurposes, it is desirable that the whole history of coaland lignite beds, and of peat and turf, should be gene-rally understood by every one using any or all of thesesubstances extensively.
Vegetable matter consists of particles of carbon withminute proportions of several other elements arrangedround minute cavities or cells, many of these being me-chanically connected to form the varieties of vegetablefibre. A large quantity of water is also present, and solong as the vegetable lives there is a constant change andcirculation of material particles kept up, replacing andrenewing the different portions. When death takesplace there is a tendency to decomposition, or the sepa-ration of the whole into minute atoms, having no furtherrelation to each other. But this is frequently checkedby various conditions, such as the presence of some sub-stances derived from plants themselves, or the absenceof sufficient oxygen gas to allow the change to take place,by mixing with the carbon, and becoming carbonic acidgas, the first step in the process of destruction. Thesecauses operate constantly, but partially, and thus a largequantity of vegetable matter is always in the course ofdecomposition, while, in particular spots, a large quan-
tity is constantly being accumulated. The latter con-dition is seen in our climate in the gradual but steadyincrease of peat bogs. The former is too common torequire further notice.
2. Peat and Turf.
Accumulations of vegetable matter may be chieflycomposed either of succulent vegetation, grasses, ormarsh plants, or of trees, and the structure and condi-tion of woody fibre is well known to be very differentfrom that of grasses and succulent plants. There arethus two very distinct kinds of material preserved, theone undergoing change much less rapidly than the other,and perhaps much less completely. It is easy to provethat, from the accumulation of forest trees has been ob-tained the imperfect coal called lignite, while from marshplants and grasses, mixed occasionally with wood, weobtain peat, turf, and bog. All these substances consistto a great extent of carbon, the proportion amountingto from 50 to 60 per cent., and being generally greaterin lignite than in turf. On the other hand, the propor-tion of oxygen gas is generally very much greater inturf than in lignite. The proportion of ash is too variableto be worth recording, but is generally sufficiently largeto injure the quality of the fuel.
As a very large quantity of turf exists in Ireland ,covering, indeed, as much as one-seventh part of the island,the usual and important practical condition of this sub-stance as fuel can be best illustrated by a reference to thatcountry. This will be understood by the following ac-count of its origin abstracted from the c< Bog Report ” ofMr. Nimmo. He says, referring to cases where clayspread over gravel has produced a kind of puddle, pre-venting the escape of the waters of floods or springs, andwhen muddy pools have thus been formed, that aquaticplants have gradually crept in from the borders of thepool towards their deep centre. Mud accumulated roundtheir roots and stalks, and a spongy semi-fluid was thusformed, well fitted for the growth of moss, which now,especially spears of Sphagnum , began to luxuriate; thisabsorbing a large quantity of water, and continuing toshoot out new plants above, while the old were decaying,rotting, and compressing into a solid substance below, gra-dually replaced the water by a mass of vegetable matter.In this manner the marsh might be filled up, while thecentral or moister portion, continuing to excite a morerapid growth of the moss, it would be gradually raisedabove the edges, until the whole surface had attained anelevation sufficient to discharge the surface-water byexisting channels of drainage, and calculated by its slopeto facilitate their passage, when a limit would be, in somedegree, set to its further increase. Springs existing underthe bog, or in its immediate vicinity, might indeed stillfavour^ its growth, though in a decreasing ratio; andhere, if the water proceeding from them were so ob-structed as to accumulate at its base, and to keep it in arotten fluid state, the surface of the bog might be ulti-mately so raised, and its continuity below so totally de-stroyed, as to cause it to flow over the retaining obstacle,and flood the adjacent country.
In mountain districts the progress of the phenomenonis similar. Pools, indeed, cannot in so many instancesbe formed, the steep slopes facilitating drainage, but theclouds and mists resting on the summits and sides ofmountains, amply supply their surface with moisture,which comes, too, in the most favourable form for vege-tation, not in a sudden torrent, but unceasingly andgently, drop by drop. The extent of such bogs is alsoaffected by the nature of the rock below them. Onquartz they are shallow and small; on any rock yielding