Encyclopædia Britannica, Ninth Edition/Coal

IN its most general sense the term coal includes all varieties of carbonaceous minerals used as fuel, but it is now usual in England to restrict it to the particular varie ties of such minerals occurring in the older Carboniferous formations. On the continent of Europe it is customary to consider coal as divisible into two great classes, depend ing upon differences of colour, namely, brown coal, corre spending to the term " lignite " used in England and France, and black or stone coal, which is equivalent to coal as understood in England. Stone coal is also a local English term, but with a signification restricted to the substance known by mineralogists as anthracite. In old English writings the terms pit-coal and sea-coal are com monly used. These have reference to the mode in which the mineral is obtained, and the manner in which it is transported to market.

The root kol is common to all the Teutonic nations, while in French and other Romance languages derivatives of the Latin carbo are used, e.g., charbon de terre. In France and Belgium, however, a peculiar word, kouille, is generally used to signify mineral coal. This word is supposed to be derived from the Walloon hole, correspond ing to the mediaeval Latin kulla;. Littre" suggests that it may be related to the Gothic haurja, coal. Anthracite is from the Greek a.v6pa, and the term lithanthrax, stone coal, still survives, with the same meaning in the Italian litantrace.

It must be borne in mind that the signification now attached to the word coal is different from that which for merly obtained when wood was the only fuel in general use. Coal then meant the carbonaceous residue obtained in the destructive distillation of wood, or what is known as charcoal, and the name collier was applied indifferently to both coal-miners and charcoal-burners.

The spelling "cole" was generally used up to the middle of the 17th century, when it was gradually superseded by the modern form, "coal." . The plural, coals, seems to have been used from a very early period to signify the broken fragments of the mineral as prepared for use.

Coal is an amorphous substance of variable composition, and therefore cannot be as strictly defined as a crystallized or definite mineral can. It varies in colour from a light brown in the newest lignites to a pure black, often with a bluish or yellowish tint in the more compact anthracite of the older formations. It is opaque, except in exceed ingly thin slices, such as made for microscopic investigation, which are imperfectly transparent, and of a dark brown colour by transmitted light. The streak is black in an thracite, but more or less brown in the softer varieties. The maximum hardness is from 2 5 to 3 in anthracite and hard bituminous coals, but considerably less in lignites, which are nearly as soft as rotten wood. A greater hardness is due to the presence of earthy impurities. The densest anthracite is often of a semi-metallic lustre, resembling somewhat that of graphite. Bright, glance, or pitch coal is another brilliant variety, brittle, and breaking into regu lar fragments of a black colour and pitchy lustre. Lignite and cannel are usually dull and earthy, and of an irregular fracture, the latter being much tougher than the black coal. Some lignites are, however, quite as brilliant as anthracite; cannel and jet may be turned in the lathe, and are suscep tible of taking a brilliant polish. The specific gravity is highest in anthracite and lowest in lignite, bituminous coals giving intermediate values (see Table I.) As a rule the density increases with the amount of carbon, but in some instances a very high specific gravity is due to inter mixed earthy matters, which may be separated by me chanical treatment.

Coal is perfectly amorphous, the nearest approach to any thing like crystalline structure being a compound fibrous grouping resembling that of gypsum or arragonite, which occurs in some of the steam coals of S. Wales, and is locally known as " cone in cone," but no definite form or arrangement can be made out of the fibres. The impres sions of leaves,_ woody fibre, and other vegetable remains are to be considered as pseudomorphs in coaly matter of the original plant structures, and do not actually represent the structure of the coal itself. There is generally a ten dency in coals towards cleaving into cubical or prismatic blocks, but sometimes the cohesion between the particles is so feeble that the mass breaks up into dust when struck. These peculiarities of structure may vary very considerably within small areas ; and the position of the divisional planes or cleats with reference to the mass, and the pro portion of small coal or slack to the larger fragments when the coal is broken up by cutting-tools, are points of great importance in the working of coal on a large scale.

The divisional planes often contain small films of other minerals, the commonest being calcite, gypsum, and iron pyrites, but in some cases zeolitic minerals and galena have been observed. Salt, in the form of brine, is some times present in coal. Some years ago a weak brine occur ring in this way was utilized at a bathing establishment at Ashby-de-la-Zouche. Hydrocarbons, such as petroleum, bitumen, paraffin, &c., are also found occasionally in coal, but more generally in the associated sandstones and lime stones of the Carboniferous formation. Gases, consisting principally of light carburetted hydrogen or marsh gas, are often present in considerable quantity in coal, in a dissolved or occluded state, and the evolution of these upon exposure to the air, especially when a sudden diminution of atmospheric pressure takes place, constitutes one of the most formidable dangers that the coal miner has to encounter.

The classification of the different kinds of coal may be considered from various points of view, such as their chemical composition, their behaviour when subjected to heat or when burnt, and their geological position and origin. They all contain carbon, hydrogen, oxygen, and nitrogen, forming the carbonaceous or combustible portion, and some quantity of mineral matter, which remains after combustion as a residue or "ash." As the amount of ash varies very considerably in different coals, and stands in no relation to the proportion of the other constituents, it is necessary in forming a chemical classification to compute the results of analysis after deduction of the ash and hygroscopic water. Examples of analyses treated in this manner are furnished in the last column of Table I., from which it will be seen that the nearest approach to pure carbon is fur nished by anthracite, which contains above 90 per cent. Anthracite. This class of coal burns with a very small amount of flame, producing intense local heat and no smoke. It is especially used for drying hops and malt, and in air or blast fur naces where a high temperature is required, but is not suited for reverberatory furnaces. The American anthracite is largely used in iron smelting, as is also that of South Wales, but to a less extent, the latter having the disad vantageous property of decrepitating when first heated.

The most important class of coals is that generally known as bituminous, from their property of softening or undergoing an apparent fusion when heated to a temperature far below that at which actual combustion takes place. This term is founded on a misapprehension of the nature of the occurrence, since, although the softening takes place at a low temperature, still it marks the point at which destructive distillation commences, and hydrocarbons both of a solid and gaseous character are formed. That nothing analagous to bitumen exists in coals is proved by the fact that the ordinary solvents for bituminous substances, such as bisul phide of carbon and benzole, have no effect upon them, as would be the case if they contained bitumen soluble in these re-agents. The term is, however, a convenient one, and one whose use is almost a necessity, from its having an almost universal currency among coal miners. The propor tion of carbon in bituminous coals may vary from 80 to 90 per cent. the amount being highest as they approach the character of anthracite, and least in those which are nearest to lignites. The amount of hydrogen is from 4i to 6 per cent., while the oxygen may vary within much wider limits, or from about 3 to 14 per cent. These variations in com position are attended with corresponding differences in quali ties, which are distinguished by special names. Thus the semi-anthracitic coals of South Wales are known as dry" or "steam coals," being especially valuable for use in marine steam-boilers, as they burn more readily than anthracite and with a larger amount of flame, while giving out a great amount of heat, and practically without producing smoke. Coals richer in hydrogen, on the other hand, are more useful for burning in open fires smiths forges and furnaces where a long flame is required. The excess of hydrogen in a coal, above the amount necessary to combine with its oxygen to form water, is known as " disposable " hydrogen, and is a measure of the TABLE I. Elementary Composition of Coal (the figures denote the amounts per cent}. Composition calculated exclusive of Water, Sulphur, and Ash. Localities. Specific Gravity. Carbon. Hydrogen. Oxygen. Nitrogen. Sulphur. Ash. Water. Carbon. Hydrogen. 0. and N. A ntUracite. 1. South Wales 1-392 1-462 90-39 90-45 82-70 75-49 86-80 78-65 78-57 79-90 80-07 63.10 82-67 79-34 63-29 66-31 50-72 3-28 2-43 1-41 4-73 4-25 4-65 5-29 4-85 5-53 8-91 9-14 10-41 4-98 5-63 5-34 2-98 2-45 o- 6- 3- 13- 12-88 12-75 8-08 7- 8" 4- 26- 22-86 33-18 0-83 85 78 06 36 1-84 0-64 2-12 25 19 33 24 0-57 2-80 0-91 10-35 1-21 0-83 0-55 0-39 0-20 1-50 0-96 5-32 2-36 0-90 1-61 4-67 3-75 10-67 4-40 2-49 1-03 1-66 2-70 19-78 8-49 2-36 7-86 2-00 0-94 1-12 0-66 1-13 0-91 93-54 94-89 97-34 86-78 92-24 80-67 79-70 81-45 85-48 79-61 82-67 83-80 66-97 69-53 55-11 3-39 2-54 1-66 5-43 4-51 4-76 5-37 4-92 5-90 11-24 9-14 10-99 5-27 5-90 5-80 3-82 2-57 1-00 7-79 3-25 14-5 14-9 13-63 8-62 9-15 8-19 5-21 27-76 24-57 39 09 2 Pennsylvania 3. Peru Bituminous Steam mid Coking Coal. 4. Eisca, South Wales 5. Aberdare, Do 6. Hartley, Northumberl d 7. Dudley, Staffordshire ... 8. Strauitzen, Styria 1-278 Cannel or Gas Coal. 9. Wigan, Lancashire 10. Boghead, Scotland 11. Albertite, Nova Scotia.. 12. Tasmanite, Van Die- ) man s Land. ( 1-276 1-18 1-100 Lignite and Broivn Coal. 13. Cologne 14. Bovey, Devonshire 15. Trifail, Styria fitness of the coal for use in gas-making. This excess is greatest in what we know as cannel coal, the Lancashire kennel or candle coal, so named from the bright light it gives out when burning. This, although of very small value as fuel, commands a specially high price for gas- making. Canuel is more compact and duller than ordi nary coal, and can be wrought in the lathe and polished. These properties are most highly developed in the substance known as jet, which is a variety of cannel found in the lower oolitic strata of Yorkshire, and is almost entirely used for ornamental purposes, the whole quantity produced near Whitby, together with a further supply from Spain, being manufactured into articles of jewellery at that town. _ When coal is heated to redness out of contact with the air, the more volatile constituents, water, hydrogen, oxygen, and nitrogen are expelled, a portion of the carbon bein^ also volatilized in the form of hydrocarbons and carbonic oxide, the greater part, however, remaining behind, to gether with all the mineral matter or ash, in the form of coke, or, as it is also called, "fixed carbon." The proportion of this residue is greatest in the more anthracitic or drier coals, but a more valuable product is yielded by those richer in hydrogen. Very important distinctions those of caking or non-caking are founded on the behaviour of coals when subjected to the process of coking. The former class undergo an incipient fusion or softening when heated, so that the fragments coalesce and yield a compact coke, while the latter (also called free-burning) preserve their form, producing a coke which is only serviceable when made from large pieces of coal, the smaller pieces being incoherent and of no value. The reason of this difference is not clearly made out, as non-caking coals are often of very similar ultimate chemical composition as those in which the caking property is very highly developed. As matter of experience, it is found that caking coals lose that property when exposed to the action of the air for a lengthened period, or by heating to about 300 C., and that the dust or slack of non-caking coal may, in some instances, be converted into a coherent cake by exposing it suddenly to a very high temperature. Lignite or brown coal includes all varieties which are Liguit intermediate in properties between wood and coals of the older formations. A coal of this kind is generally to be distinguished by its brown colour, either in mass or in the blacker varieties in the streak. The proportion of carbon is comparatively low, usually not exceeding 70 per cent., while the oxygen and hygroscopic water are much higher than in true coals. The property of caking or yielding a coherent cake is usually absent, and the ash is often verj> high. The specific gravity is low when not brought up by an excessive amount of earthy matter. Sometimes it is almost pasty, and crumbles to powder when dried, so as to be susceptible of use as a pigment, forming the colour known as Cologne earth, which resembles umber or CHUGIN.j (J O In Nassau and Bavaria woody structure is very common, and it is from tbis circumstance that the term lignite is derived. The best varieties are black and pitchy in lustre, or even bright and scarcely to be distinguished from true coals. These kinds are most common in Eastern Europe. Lignites, as a rule, are generally found in strata of a newer geological age, but there are many instances of perfect coals being found in such strata. By the term "ash" is understood the mineral matter re maining unconsumed after the complete combustion of the carbonaceous portion of a coal. This represents part of the mineral matter present in the plants from which the coal was originally formed, with such further addition by infiltration and mechanical admixture as may have arisen during consolidation and subsequent changes. The com position of the ashes of different coals is subject to consi derable variation, as will be seen by the following list of analyses : TABLE II. Composition of the Ashes of Coals.

| a iS . 1 o 1 a o a> o a 22 Us 1 | ifl 1 & a o f! o 2< 1 99 3 feO ^ SU w

H True Coals. Dowlais, South Wales 39-64 39-20 11-84 1-81 2-58 3-01 98-03 Ebbw Vale, do. 53-00 35-01 3-94 2-20 4 -89 0-88 99-92 Konigsgrube. Silesia. 55-41 18-95 16-06 3-21 1-87 2-05 1-73 0-36 99-IH Ohio 44-60 41-10 7 40 3-61 1-28 1-82 69 0-29 IOU 69 Lignites. Helmstadt, Saxony... 17-27 11-57 5-57 23-67 2-58, 2-64 33-83 97-13 Edele"ney, Hungary.. S6-01 23-07 5-05 15-62 3 64 2-38, 12-35 98-12 The composition of the ash of true coal approximates to that of a fire-clay, allowance being made for lime, which may be present either as carbonate or sulphate, and for sulphuric acid. The latter is derived mainly from iron pyrites, which yields sulphate by combustion. An indi cation of the character of the ash of a coal is afforded by its colour, white ash coals being generally freer from sulphur than those containing iron pyrites, which yield a red ash. There are, however, several striking exceptions, as for instance in the anthracite from. Peru, given in Table I., which contains more than 10 per cent, of sulphur, and yields but a very small percentage of a white ash. In this coal, as Avell as in the lignite of Tasmania, known as white coal or Tasmanite, the sulphur occurs in organic com bination, but is so firmly held that it can only be very partially expelled, even by exposure to a very high and continued heating out of contact with the air. An anthracite occurring in connection with the old volcanic rocks of Arthur s Seat, Edinburgh, which contains a large amount of sulphur in proportion to the ash, has been found to behave in a similar manner. Under ordinary conditions, from |- to ^ of the whole amount of sulphur in a coal is volatilized during combustion, the remaining | to |- being found in the ash. The amount of water present in freshly raised coals varies very considerably. It is generally largest in lignites, which may sometimes contain 30 per cent, or even more, while in the coals of the coal measures it does not usually exceed from 5 to 10 per cent. The loss of weight by exposure to the atmosphere from drying may be from -g- to of the total amount of water contained. Coal is undoubtedly the result of the transformation of vegetable matter, mainly woody fibre, by the partial eli mination of oxygen and hydrogen giving rise to a substance richer in carbon than the original wood, the mineral matter being modified simultaneously by the almost entire removal of the alkalies and lime, and the addition of materials analagous iu composition to clay, as will be seen by comparing the analyses in Table IL The ^ L 47 following table, given by Percy, shows the relative pro portions of the different components of mineral fuels. TABLE III. Composition of Fuels (assuming Carbon - 100). Caibon. Hydro gen. Oxygen. Disposable Hydrogen. Wood 100 12-18 83-07 rso Peat 100 9 85 55 67 2 89 Lignite 100 8 37 42 42 3 07 fiiiek Coal, S. Staffordshire.. Hartley Steam Coal 100 100 6-12 5 91 21-23 18-32 3-47 3 62 South Wales Coals . . 100 475 5-23 4 09 Amevicaii Anthracite . 100 2 84 1 74 2 63 Mohr has computed that the transformation of wood into coal is attended with a loss of about 75 per cent, in weight ; and, having regard to the difference in density of the two substances, the volume of the coal can only be from -jY to i of the woody fibre from which it is derived. The nature of the change is essentially a slow oxidation under water or any covering sufficient to protect the dead wood from the direct action of atmospheric air, as -in the latter case the vegetable mould or humus would be pro duced. The products of such decomposition vary with the length of time and the nature of the plants acted on, and in the case of anthracite the change is so great that no portion of the original plant structure can be recognized, at the same time the density and conductivity for heat and electricity are increased. This, however, is a case of metamorphosis analogous to the transformation of sedi mentary into crystalline rocks, the extreme term of such metamorphosis being the production of graphite or plum bago. Daubre"e has shown that wood may be converted into anthracite by exposure to the actiun of superheated water at a temperature of 400 C. The plants concerned in the production of coal vary very Coal-pi > considerably in different geological periods. In the coal d " cui measures proper, acrogens, ferns, equise turns, and similar * allied forms are most abundant. It is stated by some observers that entire beds of coal are sometimes made up of the spores of ferns. This, however, appears to depend upon the inspection of microscopic sections, and may not be capable of rigorous quantitative demonstration. In the coals of newer date exogenous wood and leaves are more common than in those of the coal measures ; the former also contain resins, sometimes in considerable quantity. The number of species of land plants in the British sedimentary formations, which may be taken as a measure of the comparative prevalence of coal in the different series, is as follows : Devonian strata 9 species, Carboniferous do 320 Permian do 20 Triassic do 9 Lias and Oolitic do 160 Purbeckand Wealden do 38 Cretaceous do ^ Tertiary do 224 The most generally received opinion is that much if not all coal results from the transformation of plants upon the site of their growth. The principal evidence in favour of such a supposition is afforded by the common occur rence of a bed of clay, the so-called " wider-clay," con taining the roots of plants, representing the old soil, immediately below every coal seam a fact that was first pointed out by the late Sir W. E. Logan in South Wales. In Yorkshire the same thing is observed in the siliceous rock called ganister occurring in similar positions, show ing that the coal plants grew there upon sandy soils. The action of water in bringing down drift wood may have also contributed some material, but much less than the local growth. This may probably have been concerned 48 G A L [SEQUENCE OF STRATA. in the production of the very thick masses of coal of small extent found in some coal-fields in Southern Europe. Another theory, that proposed by Dr Mohr, deserves notice, namely, that coal may be of marine origin and derived from the carbonization of sea weeds, such as the great kelp plant of the Pacific Ocean. This has been very ingeniously elaborated by the author, and much apparently .rood evidence adduced in support (see his Geschichte ckr Erde Bonn, 1875). But the positive evidence afforded by roots found in the under clays is sufficient to render such an hypothesis unnecessary in the majority of instances. It must be remembered, however, that, although cellulose or wood fibre is most probably the chief material concerned in the production of coal, this substance is readily con vertible into dextrine by the action of protein or analogous fermentescible matters containing nitrogen, a change that is attended with the loss of structure, the fibre being con verted into a gummy mass. Some forms of cellulose, such as that in the lichens known as Iceland moss, are soluble in water, and are without fibre. The preservation of recogniz able woody tissue therefore in coals can only be regarded as accidental, and any argument founded upon the relative quantity of the recognizable vegetable structures in mi croscopic sections is likely to be unsound, unless the rela tive durability of the different portions of the plants be taken into account. Thus the bark of trees is, as a rule, less perishable than the solid wood, while tissues im pregnated with resinous matters are almost indestructible by atmospheric agency. Instances of this are afforded by the fossil trees found in the coal measures, which are often entirely converted into siliceous masses, the bulk of the wood having decayed and been replaced by silica, while the bark is represented by an external layer of bright coal. Fossil resins, such as amber, are of common occurrence in coals, especially those of secondary or tertiary age. In an investigation of the coking properties of the Saar- briicken coals by Schondorff, it was found that they could be separated into three different materials, which he dis tinguished as glance or bright coal, dull or striped coal, and fibrous coal. The last, which is known in England aa "mother of coal," resembles a soft, dull, black charcoal, containing abundant traces of vegetable fibre, and yielding a high proportion of non-coherent coke, behaving, in fact, like charcoal. The bright or glance coal is without any apparent structure, cleaving into cubical masses, contains but little mineral matter, and yields a strong coke. The striped coal consists mainly of a dull substance, with fine alternations of bright matter, and is essentially a gas coal yielding only an inferior coke. These differences are sup posed to be due to original differences in the substances from which the coals have been derived. Thus the fibrous coal may result from unaltered cellulose, the glance coal from the insoluble mucilage derived from the maceration of the plants in water, and the dull coal from the soluble parts, such as gum and dextrine, either original or produced by the transformation of cellulose and starch. That some thing analogous to a pulping process has gone on in the pro duction of coal is evident from the intimate intermixture of the mineral matter constituting the ash, which is quite unrecognizable before burning in the majority of instances. F. Muck (Chemische Aphorismen iiber Steinkoklen, Bochum, 1873) has recorded some interesting experiments on the behaviour of the three isomeric carbohydrates, cellulose, starch, and gum arabic, which are all of the same ultimate composition, namely, C (! H 10 5 . When sub jected to the process of coking, cellulose, in the form of Swedish filter paper, gave a residue of 6-74 per cent, of a perfectly non-coherent coke, starch 11-30 per cent, of a bright vesicular coke like that from strongly coking coal, and gum-arabic 2042 per cent, of a hard dull coke re sembling that produced from imperfectly coking gas coals. The volume of gas given off by cellulose and starch is? much larger and of a higher illuminating power than that produced from gum under the same conditions. The conditions favourable to the production of coal seem therefore to have been forest growth in swampy ground about the mouths of rivers, and rapid oscillation of level, the coal produced during subsidence being covered up by the sediment brought down by the river forming beds of sand or clay, which, on re-elevation, formed the soil for fresh growths, the alternation being occasion ally broken by the deposit of purely marine beds. We might therefore expect to find coal wherever strata of estuarine origin are developed in great mass ; and this is actually the case, the Carboniferous, Cretaceous, and Oolitic series being all coal bearing horizons, though in un equal degrees, the first being known as the coal measures proper, while the others are of small economic value in Great Britain, though more productive in workable coals on the continent of Europe. The coal measures which form part of the Palaeozoic or oldest of the three great geological divisions are mainly confined to the countries north of the Equator, Mesozoic coals being more abundant in the southern hemisphere, while Tertiary coals seem to be tolerably uniformly distributed irrespective of latitude. The nature of the coal measures will be best understood g e qu< by considering in detail the areas within which they occur of cai in Britain, together with the rocks with which they are ifer l most intimately associated. The general succession of these " rocks is given in fig. 1 (cols. 1 to 4), which is taken from Q Z tiTUU] .j

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1 -- Cv--. - - GANKTER CPAL B Old Red Sandstone /i o Lower St seen in rat, tin 1C g Shale "ej OM Red Sancfsfonc " - SOFT BED COW. 1.6 CLAY COAL Rough Rock 1 [Dei/onian] area 8 ~ ." [Oci/071KUl] r i Millstone Grit FIG. 1. Succession of Carboniferous Strata.

the index of strata issued by the Geological Survey. The

ENGLISH COAL-FIELDS.]

commencement of the carboniferous period is marked by a mass of limestones known as the Carboniferous or moun tain limestone, which contains a large assemblage of marine fossils, and has a maximum thickness in S.W. England and Wales of about 2000 feet. The upper portion of this group consists of shales and sandstones known as the Yoredale Rocks, which are highly developed in the moor land region between Lancashire and the north side of Yorkshire. These are also called the upper limestone shale, a similar group being found in places below the limestone, and called the lower limestone shale, or, in the North of England, the Tuedian group. Going north ward the beds of limestone diminish in thickness, with a proportional increase in the intercalated sandstones and shales, until in Scotland they are entirely subordinate to a mass of coal-bearing strata, which forms the most pro ductive members of the Scotch coal fields. The next member of the series is a mass of coarse sandstones, with some slates and a few thin coals, known as the Mill stone Grit, which is about equally developed in England and in Scotland. In the southern coal-fields it is usually known by the miners name of Farewell Rock, from its marking the lower limit of possible coal working. The Coal Measures, forming the third great member of the car boniferous series, consist of alternations of shales and sand stones, with beds of coal and nodular ironstones, which together make up a thickness of many thousands of feet from 12,000 to 14,000 feet when at the maximum of deve lopment. They are divisible into three parts, the lower coal measures, the middle or Pennant, a mass of sandstone con taining some coals, and the upper coal measures, also con taining workable coal. The latter member is marked by a thin limestone band near the top, containing Spirorlis carboiiarius, a small marine univalve. The uppermost portion of ihe coal measures consists of red sandstone so closely resembling that of the Permian group, which are next in geological sequence, that it is often difficult to decide upon the true line of demarcation between the two formations. These are not, however, always found together, the coal measures being often covered by strata belonging to the Trias or upper New Hod Sandstone series. The areas containing productive coal measures arc usually known as coal fields or basins, within which coal occurs in more or less regular beds, also called seams or veins, which can often be followed over a considerable length of country without change of character, although, like all stratified rocks, their continuity may be interrupted by faults or dislocations, also known as slips, hitches, heaves, or troubles (fig. 2). Fia. 2, representing a seam of coal k, worked towards m, interrupted by faults or hitches. The fault at AC is called an upthrow, that at BD a downthrow. The thickness of coal seams varies in this country from a mere film to 05 or 40 feet; but in the south of France and in India masses of coal are known up to 200 feet in thickness. These very thick seams are, however, rarely constant in character for any great distance, being found commonly to degenerate into carbonaceous shales, or to split up into thinner beds by the intercalation of shale bands or partings. One of the most striking examples of this is afforded by the thick or ten-yard seam of South Staffordshire, which is from 30 to 45 feet thick in one connected mass in the neighbourhood of Dudley, but splits up into eight seams, which, with the intermediate shales and sandstones, are of a total thickness of 400 feet in the northern part of the coal-field in Cannock Chase. Seams of a medium thickness of 3 to 7 feet are usually the most regular and continuous in character. Cannel coals are generally variable in quality, being liable to change into shales or black-band ironstones within very short horizontal limits. In some instances the coal seams may be changed as a whole, as for instance in South Wales, where the coking coals of the eastern side of the basin pass through the state of dry steam coal in the centre, and become anthracite in the western side. British Coal-fidds. There are about twenty principal coal-fields of Great Britain, besides several smaller ones, whose position is shown in Plate I., which may be classed under three heads: 1. Those forming complete basins, entirely cir cumscribed by the lower members of the carboniferous series ; 2. Those in which one limb of the basin only is visible, the opposite one being obscured by Permian or other strata of newer date; and 3. Those in which the boun daries are formed by faults, which bringdown the upper overlying strata into contact with the coal measures. The South Wales and Dean Forest basins are examples of the first of the above classes, the North of England and Yorkshire and Derbyshire fields of the second, and the South Staffordshire of the third. The last two classes are of the greatest geological interest, as giving rise to the important problem of their probable extension within workable limits beneath the overlying strata. Examples of the three different cases are given in Plate II., the first being represented by the section across the Forest of Dean, fig. 1 ; the second by that of the Lancashire coal-fields, fig. 2 ; and the third by the North Staffordshire section, fig. 3. The largest and most important of the British coal-fields South is that of South Wales, which extends from Pontypool in Wales Monmouthshire on the east, to Kidwelly in Pembrokeshire, a length of about 50 miles, and from Tredegar on the north to Llautrissant on the south, a breadth of about 18 miles, in addition to which a further narrow slip of about 20 miles long, E. and W., extends across Pembrokeshire. Excluding the latter portion, it forms a complete basin of an approximately elliptical shape, surrounded by older rocks, the Carboniferous limestone and Devonian shale dipping generally towards the centre. The basin-shaped structure is, however, modified by a central anticlinal axis, which brings the lower bed within reach of the surface. The total thickness of the coal measures is estimated at about 11,000 feet on the south, and 7000 feet on the north side in the western district. In the central portion between Britton Ferry and the River Taff, it diminishes to 4800 feet on the north side, and is still further reduced in Mon mouthshire and on the eastern side generally to about 2500 feet. The coal-bearing portions are divisible into three groups, known as- - 1. Upper Pt imant series. 2. Lower Pennant series. 3. White Ash series. The Upper Pennant series attains the maximum develop- VI. 7 50 GAL [COAL-FIELDS. merit of about 3000 feet on the south rise of the measures near Swansea; at Neath the thickness is reduced to about 1200 feet and in Monmouthshire to between 500 and 7W feet It contains all the free burning and bituminous coals of the Swansea and Neath districts, and the house- coals of Monmouthshire and the eastern districts, which latter contain 26 seams above 12 inches thick, making a total of about 100 feet of coal, an amount that increases westward to 82 seams and 182 feet. The Lower Pennant series averages from 1100 to 1500 feet between the faff Vale and Llanelly, but on the north side of the anticlinal thickens to 3000 feet. The average total of workable coal in seams which do not exceed 3 feet is 25 feet, among which are some fair steam coals, associated in places with black-band ironstone and good manufacturing and house hold coals, yielding slack suitable for coking, the most valuable among them being those of the Rhondda valley. The lowest or White Ash series contains the bulk of the valuable steam and iron making coals which have given the coal field its great reputation. It is about 500 feet thick on the eastern side, and about 1000 feet in the centre of the basin. The coals and accompanying ironstone are generally thicker and more abundant on the south than^on the north coast. The workable coals in this division amount to about 50 feet, in seams varying from 3 to 9 feet in thickness. The western extension into Pembrokeshire belongs to this part of the series ; it covers about 70 square miles, extending in a narrow east and west belt, varying from 2 to 6 miles in breadth from Tenby to St Bride s Bay. The measures are very much dis turbed, but are probably about 1500 feet, containing in the upper 1000 feet 8 seams of anthracite of about 18 feet total thickness. The total area of the coal-field is about 1000 square miles, of which amount about 153 square miles lie beneath the sea in Swansea and Carmarthen Bays. Only one square mile is covered by newer formations. According to the quantity of the coal produced, the area fs divided as follows : Bituminous coal district 410 square miles. Anthracite, ,, 410 ,, Intermediate, or Semi- Anthracite ...180 ,, The most valuable class of South Wales coals is the semi-anthracite or smokeless steam coal of the lower measures, which is in constant demand for the use of ocean steamers all over the world. It is principally ex ported from Cardiff, Neath, and Swansea. The configuration of the ground, owing to the deep north and south valleys of the Usk, Ebbw, Taff, Rhondda, and Neath Rivers, and the longitudinal anticlinal axis, renders the coals of comparatively easy access. The surface rises to a height of about 2000 feet above the sea-level, and in the valleys a greater vertical range is brought within working limits than is the case in any other coal-field of similai thickness. Forest of The Forest of Dean basin is an outlying portion of that Dean coal- O f South Wales, from which, as is shown by Ramsay, it has been separated by denudation. It is of triangular form, occupying an area of 34 square miles, between the Wye and the Severn estuary, with a total thickness of 2765 feet and 31 seams, together 42 feet thick, only 9 of which are above 2 feet in thickness. The depth from the surface to the bottom of the basin, in the centre, is about 2500 feet The lower beds of sandstone and the Carboniferous lime stone contain considerable quantities of brown hematite, ir irregular deposits, which is smelted in part on the spot anc partly exported to other districts. Owing to the symme trical basin-shaped form of the measures (Plate II. tig. 1) the coals have been worked from the surface downward along the outcrops of the seams, leaving large hollows fo he accumulation of water, which render the working of the ower ground difficult, on account of the great pumping- ower required to keep down the water flowing in from the Id shallow mines. North of the Malvern Hills a straggling patch of coal Severn neasures extends about 35 miles N. and S., from near Bailey Worcester to Newport in Shropshire. This is divisible into co wo nearly equal areas of triangular form. The southern >art is known as Forest of Wyre, and the northern as Cole- >rookdale. The former is unimportant, having a great hickness of measures which rest directly on the Devonian ocks, but scarcely any workable coal seams. The Cole- )rookdale measures rest upon the Upper Silurian rocks, are ibout 800 feet thick, with about 50 feet of coal in 18 earns, and many beds of nodular ironstone, which has iven the district a celebrity in the production of iron work, especially high-class castings. The eastern boundary s concealed by overlying Permian strata, and it was for merly supposed that the productive measures had been removed by denudation on this side ; but there is little loubt of their continuity towards South Staffordshire. To the westward of Colebrookdale are the two small fields of Leebotwood and Shrewsbury. These lie on the Silurian rocks. The exposed area of the former extends o 1 2 square miles ; that of the latter (which stretches in a crescent shape to the south and west of Shrewsbury) to L8. Both are partly hidden by Permian strata. The South Staffordshire coal-field extends about 22 miles S. Staf i fl". and S., from Rugeley to Halesowen, with a greatest * ire C( ; )readth of about 1 miles from Wolverhampton to Oldbury. [t is entirely surrounded byNewRed Sandstone rocks, which in some places are faulted against the coal measures, render ing it difficult to decide upon the chances of a profitable ex tension beneath the visible boundaries. The coal measures rest upon the Upper Silurian rocks, which are exposed at several points within the area, especially at Dudley and the Wren s Nest. This district is remarkable as containing the thickest known coal seam in England, the Thick or Ten Yard Seam, which varies from 30 to 45 feet in thick ness in the neighbourhood of Dudley, but splits up north wards into several thinner seams in the northern or Cannock Chase district. There are 6 principal seams, with a total of from 57 to 70 feet in 1309 feet of measures. The field was formerly very productive of clay ironstone, but the supply has now considerably diminished. The coals are also subject to curious alterations in places, from the in trusion of igneous rock, especially in the Rowley Hills, near Dudley. The Warwickshire or Tamworth coal-field is a narrow strip of measures, with a maximum thickness of 3000 feet, extending about 12 miles in a N.W. and S.E. line from Coventry to Tamworth. It contains 5 seams, which are mainly worked for house coal and steam purposes. It is entirely surrounded by New Red Sandstone strata, ex cept for a short distance near Atherstone, where it is seen to rest upon the millstone grit, which is altered into quartzite by intrusive igneous rocks. The Leicestershire or Ashby coal-field is an irregular Leicesl patch of 30 square miles, on the east side of Charnwood *j^ c Forest, about midway between Leicester and Burton-on- Trent. It has 7 principal seams, and probably rests upon the mountain limestone, except at the eastern end, where it may lie upon the old slatey rocks of Charnwood Forest. Southward it extends under the New Red marl towards Leicester. In the centre is a patch of barren measures upon which the town of Ashby-de-la-Zouche stands, after which the coal-field is often named. The eastern side, wuich contains the mines of Whitwick, Snibston, and Cole- Orton. contains some igneous rocks apparently connected with those of Charnwood Forest, which are not seen on the ENGLAND.] COAL 51 Z byshire K York- f e coal - II. western or Moira side, which contains the more important workings, None of the seams occurring in either division can be identified with certainty in the other, although only a few miles distant. The total thickness of the coal measures is about 2500 feet, the principal seams occurring about the middle, as is also the case in Warwickshire. North of the Trent the carboniferous strata present a more complete and regular development than is seen in the central coal-fields. The Carboniferous limestone and millstone grit formations form a central ridge of high moorlands and hills, the so-called Pennine chain, in a gently sloping anticlinal, running nearly north and south from the north of Derby shire to the borders of Scotland. The coal measures occur on both flanks of this ridge, the largest connected mass being that of the Derbyshire and Yorkshire coal field, which extends north and south for about 60 miles from Bradford to within a few miles from Derby, where it is covered by the New Bed Sandstone formation. The exposed breadth varies from 9 miles at the south end to 22 miles at the north. The measures dip regularly at a low angle to the eastward, and pass under the Permian or magnesian limestone formation, which forms the eastern boundary continuously from Nottingham through Worksop and Doncaster to Wakefield. The total thickness of measures is about 4000 feet (with about 20 seams), be longing to the middle and lower ganister series, the upper series being absent. A generalized section of the strata in this coal-field is given in the fifth column of fig. 1. The principal seams are the Black shale, or Silkstone, from 5 to 7 feet thick, which is extensively worked as a house coal, and the Top hard, or Barnsley coal, which is much used for steam purposes. At the north end of the field, in the neighbourhood of Leeds and Bradford, two thin seams, known as the Low Moor black bed and better bed, remarkable for their exceptional purity, are used for iron-making purposes at Bowling and Low Moor. Iron ores are also found in considerable quantity on the Derbyshire side of the field, which are smelted at Butterly and other works near Chesterfield. The area covered by the magnesian limestone formation has been proved by several borings and sinkings, the first winning having b?-n opened at Shireoak near Worksop, where the Top hard coal was reached at 1548 feet below the surface. It is estimated that about two-thirds of the total area of this field is to be looked for within the concealed part. On the west side of the Pennine axis, and between the same parallels as the Derbyshire and Yorkshire coal-fields, are those of North Staffordshire and Lancashire, which ex tend from Longton on the south to Colne on the north, the continuity being, however, broken by a small fold of the Carboniferous limestone shales, which is brought to the surface between Macclesfield and Congleton. Parallel to this group, however, and to the eastward of it, is situated the small but important coal-field of North Staffordshire, also known as the Pottery coal-field. It has an exposed area of about 94 square miles, which is very irregular in form, being 17 miles in greatest breadth E. to W., and about 13 miles from N. to S. The south-eastern portion, which is nearly detached, is known as the basin of Cheadle, or Froghall, which is chiefly remarkable for a band of cal careous iron ore formerly exported to Staffordshire, but now nearly exhausted. The main or western portion con sists of a mass of strata about 5000 feet thick, with 37 searns of coal, out of which 22, measuring together 97 feet, are over 2 feet in thickness ; in addition to which there are many valuable beds of ironstone, both argillaceous and black-band. The strata, which are less regularly arranged than those of S. Lancashire, as will be seen by the trans verse sections, figs. 2 and 3 in Plate II., being bent in contrasted curves, and much broken by faults, form the eastern limb of a basin having a general westerly dip, which carries them in a short distance below the New lied marl plain of Cheshire. The Lancashire coal-field is of an irregular four-sided Lancashire form. The greatest breadth, from Oldham on the east to coal-field. Saint Helen s on the west, is about 52 miles, and the length, from Burnley on the north to Ashton-under-Lyne, about 1 9 miles. Within the area are, however, two large islands of the millstone grit, which divide the northern or Burnley district from the main coal-field of Wigan and Manchester. This barren area is about compensated by a tongue of coal measure, which extends southward from Stockport to Macclesfield. The thickness of the measure is A ery great, and as the ground is much broken by faults, and the beds dip at a high angle, the workings have extended a greater depth than in any other district, the deepest workings being at Rose Bridge pits near Wigan, which have been sunk to 815 yards, and at Dukinfield, east of Manchester, where the Astley pit is 672 yards deep, and the coals have been wrought to a total depth of 772 yards by inclines. The greatest thickness is observed in the Manchester dis trict, where the total section is as follows, according to Hull. Upper Coal Measures 2013 feet. Middle Coal Measures 4247 feet. Lower Coal Measures Ganister, 1370 feet. Millstone Grit, Limestone Shale, about Limestone series, 600 feet To Oppenshaw Coal, 600 To Yard Coal, 485 Barren Measures, 1678 Unknown Strata, Sod Mine to Black Mine, ... 2000 Black Mine to Royley Mine, 897 Eoyley Mine to Kougk Rock, 1370 2000 ... 2000 There is a total of 100 feet of coal in workable seams (exceeding 2 feet), which are chiefly situated in the 3000 feet forming the bottom of the middle and top of the lower coal measures. In the Wigan district there are 18 workable seams, about 65 feet in all, the total section being: Upper Measures, barren, .................. 1500 feet. Middle Measures, mass seams, ......... 2550 ,, Ganister Measures, ....................... 1800 , , The Wigan district is remarkable for the production of a large quantity of cannel coal. In the Burnley district the lower and middle coal measures together are from 2500 to 3000 feet in thick ness, the upper measures being unrepresented. The coal-field of Northumberland and Durham lies north of that of Yorkshire, on the east side of the Pennine axis. In the intermediate ground between Leeds and Darlington, about 55 miles, the lower Carboniferous rocks are directly overlain by the magnesian limestone, which preserves the north and south course observed further south until it reaches the sea at the mouth of the Tyne. The coal-field extends north and south from Darlington through Durham to the mouth of the Coquet, about 65 miles, with a greatest breadth of about 22 miles in Durham. From the Tyne to the Coquet the eastern boundary is formed by the sea, while in the remaining area, from the Tyne to the Tees, which is included in Durham, the coal measures dip beneath the magnesian limestone. The measures are, as a rule, very regular, their dip being lower than that observed in other districts.. ;The total thickness is about 2000 feet, with 16 seams of coal, together about 47 feet thick. The millstone grit is continuously exposed below the coal measures along the eastern edge as far as the Tees, where it is overlapped by the magnesian lime stone and Triassic rocks, so that there is a portion of the coal-field hidden beyond the exposed southern bound ary, but the extent is probably not large. The seaward extension has been proved in several deep mines in the Nortlmm- berland anc * ^ ur ~ C COAL [COAL-FIELDS. neighbourhood of Sundcrland, more especially at Ryhope and Monkwearmouth which are worked at a depth of about 1850 feet to a short distance from the shore. At these points the coals are nearly flat, but at Harton, near Shields, they rise to the eastward, proving that the centre of the basin has there been passed. The best estimate gives 1 1 feet of coal, and about 1 G square miles of area, as the probable extent of this submarine portion of the coal measures. The character of the coal produced varies in the different parts of the basin. The southern and western districts adjoining Bishop Auckland and Ferry hill produce a strongly caking coal, which is chiefly employed in the manufacture of a pure and dense coke for use in the Cleveland and Cumberland iron works, a considerable amount being also exported for foundry use. The central district, adjoining Newcastle and Sundcrland, produces the best class of house coal, known in London under the name of Wallsend, from the pits on the Tyne where it was originally mined, .which were close to the eastern termination of the wall built by the Romans to protect the country between the Tyne and the Solvvay from the incursions of the Picts. These collieries have been long since abandoned, but the name is still given in the London market to the best Durham house coals, and even to much that has been produced in other places, as indicating a coal of superlative excellence. The great merit of Wallsend coal is in its small proportion of ash, which also, being dark -coloured, is not so obtrusive on the hearth as the white ash generally characteristic of the Midland coals. The strongly caking property, and the large amount of gas given out in burning, tend to produce a bright and enduring fire. In. the district north of the Tyne the produce is principally steam coal, which is known as Hartley coal, being named after one of the principal collieries. It is largely used for sea-going steamers, and was lately in use in the Royal Navy mixed with South Wales coal, a combination which was supposed to give a higher evaporating value in raising steam than when either class was burnt alone. Although of a lower calorific power, and making more smoke than South Wales coal, the north country coal deteriorates less rapidly than the former when stored in hot climates. There are two small coal-fields in the mountain limestone district of the Tyne near Hexham, and another on the Solway at Can- nobie; these are, however, of small importance. The Cumberland field extends along the coast of the South Irish Channel from Saint Bees northward for 15 miles to Maryport, where it turns eastward for about 1 7 miles, and is exposed with constantly diminishing breadth until it disappears under the Permian rocks of the Vale of Eden. The greatest breadth is about 5 miles at White- haven and Workington, but. as in Northumberland and Durham, the beds dip and the coals have been worked below the sea to a distance of 1 J miles from the shore or 2 miles from the pit. The total thickness of the mea- sitres is 1500 feet, with three workable seams. The pro duce is largely consumed within the district, a considerable portion of the export being to Belfast and other Irish ports. Denbigh- The coal measures of North Staffordshire and Lanca shire reappear on the western side of the plain of Cheshire coal -fields. in the coal - nelds of Denbighshire and Flintshire, which form a nearly continuous tract from the neighbourhood of Oswestry through Ruabon and Wrexham to the mouth of the Dee, and along the Welsh coast near Mostyn. The .separation between them is formed by a slight roll in the mountain limestone near Gresford, corresponding to that dividing the two coal-fields on the eastern out-crop. The Denbighshire field is about 18 miles long, having 7 seams, together from 26 to 30 feet in thickness. The principal workings are near lluabon, where there are several large coal collieries producing a much esteemed house coal. The Flintshire field is about 15 miles long. The greatest breadth is in the neighbourhood of Mold, whence it nar rows in a N.W. direction, being covered by the estuary of the Dee. At Mostyn coal has been extensively worked under the river, but great difficulty was experienced in keeping the mines clear of water. The details of the measures in this district have not been fully worked out, but the southern portion is the most valuable. The higher measures contain six seams, including some valuable beds of caunel, the total being about 28 feet. In the northern district bordering the Dee the beds are much disturbed by faults, but the deeper coals are said to be of good quality. The basin formed by the North Wales, Lancashire, and North Staffordshire coal-field is probably the most extensive tract of coal measures in the country, as it may be assumed to extend under the overlying Triassic strata under the Dee and the Mersey to South Lancashire and across the plain of Cheshire, an area of 800 to 1000 square miles. Much of this, however, is far beyond workable limits, the depth to the top of the coal measures being estimated at 10,000 feet below the surface at the point of greatest depression. The area within the limits of 4000 feet below the surface, which has been assumed as a possible maximum working depth, may be seen by refer ence to Plate I. There is a small coal-field in the Island of Anglesea, which is interesting for its geological peculiarities, but it is of very small economic value. The Somersetshire coal-field appears at the surface in the form of several disconnected patches, the largest of which extends northward of Bristol for about 12 miles, while the remainder stretches southward for about the same distance to the Mendip hills. The Carboniferous lime stone is seen at many places along the western flank, but the connection is generally hidden by a peculiar modifi cation of the New Red Sandstone known as the Dolomitic Conglomerate, which overlaps both formations indifferently. Towards the east the measures are further obscured by the overlap of the lias and oolitic rocks, this being the only field in which such an overlap takes place in England. The exposed area of the coal measures is only about 14 square miles, but it is estimated that they extend over 238 square miles, the remainder being concealed by overlying strata. The character of the measures is similar to those of South Wales and Dean Forest, namely an upper and lower pro ductive series separated by a nearly barren mass of Pen nant sandstones. The sections, which vary very consider ably, are summarized by Prestwich as follows: Upper series 2600 feet thick, with 16 seams, together 26 ft. 10 in. thick. Pennant sandstone, 2500 to SOOO ,, 4 50 Lower series, 2SUO 26 C6 6 Together, 7900 to 8400 46 93 4 The disturbance of the strata by faults is much greater than in any other British coal-field. The whole series is squeezed into a comparatively narrow trough, which throws the bottom of the basin to about 8000 feet below the surface. The coals are in some instances tilted up vertically, or even turned over, a kind of disturbance which is usually attended with considerable shattering of the strata. In one instance the upper series of measures have been shifted horizontally by an inclined or slide fault for a distance of about 200 feet above the: lower series. In spite of the difficulties caused by these disturb ances, coal seams of only a foot in thickness are regularly worked in Somersetshire, which is far below the limits considered to be profitable in other districts. The coal-bearing strata of Scotland 1 are confined to the 1 For the following account of the coal-fields of Scotland the writer is indebted to Mr J. Geikie, F.R.S. SCOTLAND.] GOAL 53 Carboniferous formation, the only exceptions being the little patch of Oolitic coal at Brora in Sutherland and certain thin seams which occur intercalated among the Miocene volcanic rocks of the Western Islands. The Scottish Car boniferous Formation is divisible into four series, viz., 1. Coal Measures; 2. Millstone Grit; 3. Carboniferous Limestone series ; 4. Calciferous Sandstone series. Coal is confined chiefly to the first and third of these groups, but in West Lothian and Mid-Lothian the lowest (calciferous sandstones) yields some coals, one of which has been worked (Houston coal, 6 feet thick). These coals are associated with the well-known " oil-shales," forming a peculiar deve lopment of the upper portion of the calciferous sandstone series which is not repeated elsewhere in Scotland. The millstone grit contains no workable coals. The coal bear ing strata of the coal measures and limestone series are irregularly distributed over the central or lowland district of the country between a line drawn from St Andrews to Ardrossan, and a second line traced parallel to the first from Dunbar to Girvan. Throughout this region the strata are disposed in a series of basins, of which there are properly speaking only three, namely, (1) The basin of Mid-Lothian and Fifeshire, which is bounded on the west by the calciferous sandstone series and some older strata, forming the Peritland hills, Arthur s Seat, the rolling ground that extends west of Edinburgh into Linlithgow- shire, and the heights behind Burntisland in Fifeshire, and in the east by the barren sandstones and igneous rocks of the calciferous sandstone series in the east of Hadding- tonshire and Fifeshire; (2) The basin of Lanarkshire and Stirlingshire, the eastern boundary of which begins in the south at Wilsontown, and runs north by Bathgate and Borrowstounness to the borders of Clackmannan, extends west to the foot of the Campsie and Kilbarchan Hills, and is separated by the Paisley and Dunlop Hills from (3) the basin of Ayrshire, the main mass of which is bounded in the south and east by the valley of the Doon, the Silurian uplands behind Dalmellington and New Cumnock, and the calciferous sandstone and Old Red Sandstone heights which overlook the heads of the Ayr and Irvine valleys. Two small outlying coal-fields lie beyond these boundary lines, viz., the Girvan and Sanquhar (Dumfriesshire) coal fields, but both belong geologically to the Ayrshire basin. Although there are thus only three great basins, it is usual, nevertheless, to speak of five principal coal-fields, each of which is named after the county in which it is roost abundantly developed. Thus we have the coal-fields of Ayrshire, Lanarkshire, Stirlingshire, Fifeshire, and Mid- Lothian. /shire. Ayrshire Coal-fields. The Ayrshire basin, owing to undulations and faultings of the strata, comprises a number of subsidiary coal-fields, such as those of Girvan, Sanquhar (Dumfriesshire), Dalmellington, New Cumnock, Lugar and Muirkirk, Kilmarnock, Kilwinning, Dairy, &c. The coal measures of this basin are of variable thickness ; they contain from 5 to 8 and 11 principal coal-seams, yielding a united thickness of from 13 ft. to 40 ft. The Carboni ferous limestone series of Ayrshire sometimes contains no workable seams of coal, while occasionally its seams eqiial or surpass in number and thickness those of the coal mea sures. Thus in the Girvan field there are 7 coals with an aggregate thickness of 50 feet, while at Muirkirk the same number yield a thickness of 40 feet of workable coal. The Ayrshire coals consist chiefly of common coals, including " hard" or " splint" and " soft" varieties. In some districts the intrusion of igneous rocks has converted certain seams into "blind coal," a kind of anthracite, much used for steam purposes. Gas or parrot coal (so called from its dr.- crepitating or chattering when heated) is met with here aud there, chiefly near New Cumnock. Parrot coal often occurs in thin lines or bands, which, when intercalated aud alternating with dark carbonaceous ironstone and coaly matter, form seams of what is called black-band ironstone. The Ayrshire black-bands occur chiefly at Dairy, Lugar, and Dalmellington. Lanarkshire Coal-fields. These are the most extensive Lanark in Scotland, covering an area of not less than 150 square shire, miles. The coal measures, which attain a thickness of upward of 2000 feet, contain about 18 workable coals; but all these are not continuous throughout the whole coal field, while some are too thin in places to pay the cost of working. At their best they yield an aggregate thickness of 70 feet or thereabout, but in many places they do not average more than 40 or 30 feet, or even less. The lime stone series is well-developed in the Lanarkshire coal-fields, but it is a very variable group, as indeed is the case throughout Scotland. It consists of upper, middle, and lower groups, tho coals being confined chiefly to the middle group, only one or two seams occurring in the lower, while in the upper only one seam occasionally attains a workable thickness. The principal coals of the limestone series vary in number from 1 to 9, their aggregate thick ness seldom reaching more than 15 feet. The Lanarkshire coals consist chiefly of varieties of common coal, namely, hard or splint, soft, dross, &c. But here and there excel lent gas coal is worked, as at Auchenheath, Wilsontown, <fec., the former being considered the finest of all the Scotch gas coals. Another well-known parrot coal is that of Bog head near Bathgate, the subject of much litigation. Par rot or gas coal frequently occurs forming a part of mussel- band and black-band ironstones, which seams, when traced along their crop, are often seen to pass into gas coal. The best known blackbands are those wrought at Palacecraig, Airdrie, and Quarter, Bellside, Calderbraes, Bowhousebay and Braco, Goodockhill and Crofthead, Earnockmuir, Possil, Garscadden, and Johnstone. At Quarrelton, Renfrewshire, an abnormal development of coal seams occurs below the horizon of the main or Hurlet limestone, which is usually the lowest important bed in the limestone series. The strata underlying that limestone contain here and there irregular lenticular patches of coal, never of any value. At Quarrelton, how ever, a number of these seams come together, and form a mass of coal more than 30 feet thick. Stirlingshire Coal-fields. These embrace the coal-fields Stirling of Falkirk, Carron, and Grangemouth, Slamannan, Clack- sllire< mannan, and Borrowstounness. In the Falkirk, Carron, and Grangemouth fields, the coal measures are about 600 feet thick, and contain 9 workable seams of coal, yielding an aggregate thickness of 30 or 31 feet; the thickest seam is only 4 feet. In the Slamannan field, the coal measures are some 720 feet thick, and show G workable coals, yielding an aggregate thickness of 15 or 16 feet, the thickest seam being 4 J feet. A small outlier of coal measures at Coney- park, however, gives a depth of 1140 feet of strata, con taining 12 workable coals (two of which are 7 feet thick re spectively), which yield an aggregate thickness of 44 feet. The coal measures of the Clackmannan district attain a thickness of 900 feet, and yield 10 workable seams of coal (thickest seam 9 feet) with an united thickness of 41 feet. The limestone measures of the Stirlingshire basins contain, as a rule, few coal seams. Where these are best developed, they vary in number from 5 (Bannockburn) to 1 1 seams (Oakley); and their aggregate thickness ranges from ll feet to 37 feet. The coals embrace the variety usually met with in Scotland, viz., hard (or splint) and soft coals, some of the seams being good caking coals. Good gas coal was formerly obtained at Oakley; and other coarse parrot coals occur in various parts of the fields. Oil shale and black- band ironstone are alsoltnet with. The coal-field of BorCOAL [COAL-FIELDS. rowstounness is remarkable for containing thick sheets of basalt rocks, which are of contemporaneous origin, and do not alter the beds that rest upon them. Mid- M id -Lothian and Fifeshire Coal Fields. The Mid lothian. Lothian coal field is disposed in what are for Scotland unusually symmetrical and unbroken lines. The basins lie with their principal synclinal axes from north to south. In the deepest basin the coal measures lie in a trough 2 miles broad and 9 miles in length, stretching from the sea at Musselburgh through Dalkeith to Carrington. The trough is underlaid by the millstone grit (Roslin Sandstone or Moor Rock), whose outcrop surrounds that of the coal measures in a band rarely more than half a mile broad. The Carboniferous limestone series rises from beneath the basin of millstone grit and coal measures on its west side, and crosses at a high angle, in a band about a mile in breadth, through Portobello, Gilmerton, and Penicuik. South of Penicuik the millstone grit forms another basin at Auchencorse Moss, but the trough is not deep enough to bring in the coal measures. West of Dalkeith the limestone series forms a shallow undulating basin with an outcrop of about 7 miles broad, extending from the sea at Cockenzie by Tranent and Pathhead. The Dalkeith basin of the coal measures has a total thickness of 1180 feet. There are 14 coal seams of a workable thickness, with an aggregate of 43 ft. 4 in. The limestone series of Mid- Lothian contains numerous coal seams. The total thick ness of the series is 1582 feet, with 23 workable coal seams, aggregating 68 ft. 3 in. The "great seam" averages between 8 and 11 feet, and in one place is 12 ft. 6 in. thick. The coals of the Mid-Lothian basins are of the usual varieties met with in Scotland. The basins of the Mid- Fifeshire. Lothian coal-fields reappear on the southern coast of Fife, and are undoubtedly continuous (though somewhat de nuded) beneath the Firth of Forth. A segment of the western half of the coal measures trough (the prolongation of that of Dalkeith) extends from Dysart by Markinch, Ken no way, and Largo Bay. On the north this trough is bounded by faults, and on the east and south it is covered by the sea. Measured from Coaltown to Methil (at right angles to the line of strike) the thickness of the coal measure strata exposed to view may be roughly estimated at 4600 feet ; but as the centre of the basin is not reached at the coast, the total thickness of strata is not seen. There are about 11 workable seams, with an aggregate of 61 feet. The Dysart Main coal is 16 feet thick. Another little basin, comprising the lower seams of the coal measures, occurs at Kinglassie. The Dysart or Leven coal measure basin occupies about 18 square miles, and that of Kin glassie from 3 to 4. The limestone series of Fife lies in several much broken basins on the south side of the Ocliils and Lomond Hills from Alloa to Earlsferry. The prin cipal coal fields in this series are those of Dunfermline, Halbeath, Lochgelly, and Kelty; but coals have been worked in many other places, as at Ceres, Radernie, Largo ^ Ward, Markinch, &c. The coal-bearing strata vary in thickness, but do not exceed 600 feet. In the Dunfermline coal-field there are 10 seams, ith an aggregate thickness of 4 1 feet, llalbeath coal-field yields < seams, with an aggregate thickness of 29| feet; Lochgelly coal-field contains some 1-i seams, with an aggregate thickness of about 65 feet ; in the Kclty and Heath coal-field there are 12 seams, yielding an aggre gate of 43i feet. The workable seams in these separate fields range in thickness from about 2 feet up to 10 and 14 feet. The 14 feet coal of Lochgelly is divided by thin ribs of stone, which thicken out eventually so as to "divide the coal into 5 separate workable seams, which, with the inter vening strata, yield a thickness of 10 fathoms of strata. It is worth noting that, in the lower Carboniferous rocks of Fifeshire, two coals are worked at Balcarmo and else where. As a rule, this series in Scotland is barren. The carboniferous strata of Ireland consist chiefly of the Carboniferous limestone, which covers the greater por tion of the island in one connected mass. The coal measures have probably been at one time nearly as exten sive, but they have been almost entirely removed by denudation, the largest remaining basins being that of Castlecomer, near Kilkenny, and another in the west, between Tralee, Mallow, and Kilarney. In the north the small basin of Coal Island, on the west side of Lough Neagh, is partly covered by New Red Sandstone strata, and trials have been made to discover a possible extension of the coal measures in the valley of the Lagan, between Belfast and Lisburn. The two coal fields of South Wales and Somersetshire Probal differ from those of the central and northern counties in their strike or direction, their longer axes being placed east and west, instead of north and south, which is the prevail- ing direction of the latter, the strata in the Somersetshire area being sharply bent and broken on a north and south line in a manner which is not seen elsewhere in this country, but is reproduced on a much larger scale in the north of France and Belgium. The most easterly point in England at which the coal measures have been worked is near Bath, where the overlying Liassic and New Red Sand stone strata are .about 360 feet thick, beneath which the coal has been followed for some 5 or 6 miles from the outcrop. From this point nothing certain is known of their extension until we reach the neighbourhood of Valen ciennes, where a coal field, known as that of Hainault and Valenciennes, extends with a general east and west strike as far as Namur, a distance of 65 miles. AtNamur the width is about 2 miles, near Charleroi from 7 to 8, and through the north of France from 6 to 7. Only the eastern half, between Charleroi and Namur, comes to the surface, the western portion being covered by Tertiary and Creta ceous strata. Within 30 miles of Calais the coal measures end, the shales of the Carboniferous limestone having been pierced in a boring of 1113 feet deep at the latter place. East of Namur the coal measures come in again at Li6ge, continuing for about 45 miles, with a width of from 3 to 8 miles to beyond Aix la Chapelle, where they are divided by a ridge of Carboniferous limestone into two parallel basins, covered by Cretaceous and newer deposits, till they appear again on the right bank of the Rhine in the valley of the Ruhr, in the great Westphalian basin, which is probably the largest in Europe. The same general structure is apparent along the whole of this line, which, from the western end of the South Wales basin to Frome, and from the N, of France to the Ruhr, is about 470 miles long. The measures generally dip regularly from N. to S. along the northern line of out crop where it is known, but on the southern side they are bent into sharp folds by the elevation force which has up lifted the underlying Carboniferous limestone and Devonian strata along an east and west line, extending from the old slaty rock of the Ardennes to the Mendip Hills and the western part of Pembrokeshire. The known coal fields extend for about 350 miles out of the above amount of 470, and from the similarity of their position and structure many gealogists are of opinion that other basins similarly placed may be reasonably supposed to exist in the intermediate ground between Somersetshire and Belgium. This subject has been treated in great detail by Mr Godwin Austen and Prof. Prestwich in the Reports of the Royal Commission upon Coal. The probable direction of this axis is shown on the map, Plate I. The only actual determinations of the rocks made within this area have been in two borings at Kentish Town and Harwich. In the former, CONTINENTAL EUROPE.] COAL sandstones, supposed to be of Devonian age, were reached below the Cretaceous strata at 1113 feet, and in the latter the Carboniferous limestone shale at 1025 feet. The most likely positions for the coal measure trough are con sidered byPrsstwich to be in Essex and Hertfordshire, while Mr Godwin Austen places them in the valley of the Thames or under the North Downs. The latter seems to be the more probable than the line further north. The point, however, is purely speculative in the absence of any trial borings as guides; and a great number of these would certainly be required before any generalization as to the position of workable coal measures even within a wide range could be accepted. The deep boring on the southern part of the Wealden area, near Hastings, which it was sup posed would have thrown a considerable amount of light on this matter, has hitherto been without other result than the proof of the existence of a totally unexpected and exceed ingly great thickness of the upper Oolitic clays, similar to what is known on the French coast, near Boulogne. On the south side of the Mendip axis a very large area in Devonshire is occupied by the lowest coal measures or culm series, which consist almost entirely of clay slates, with a few beds of anthracite in the northern portion of the district, near Barnstaple and Bideford. These are only worked to a small extent, their principal use being, not for fuel, but as a pigment for covering iron-work, which is known as Bideford black. The coal-bearing areas of Secondary and Tertiary age in the United Kingdom are of very small importance. In -p. T . ,: P ., , < <! Devonshire a lignite- bearing series of strata of Miocene age occurs in the flank of the granite of Dartmoor at Bovey Traeey, near Newton Abbot. This is principally remarkable for its associated clays, which are derived from the waste of the granite, and contain numerous impressions of dicotyledonous leaves and other plant remains. The coal is a lignite resembling a mere heap of tree stems drifted together and partially decomposed. It is nut now worked, the original excavations being filled with water; and as the demand is restricted to supplying the wants of the local potteries, there is no opening for profitable mining. - In the Great Oolite of Yorkshire, some thin seams of coal or lignite were formerly worked at numerous points upon the moors between the Cleveland Hills and the Vale of Picker ing. The most important product of this district, however, i-a the jet which is obtained from the waste of coal-bearing strata of the same age along the cliffs near Whitby, where it is manufactured into ornaments. The largest Oolitic coal deposit in this country is that of Brora in Sutherland, where a seam of about 3 feet in thickness has been worked at intervals for a considerable period, but never to any considerable extent except during the prevalence of high prices in the coal trade. Another area in which coal is found in strata of Second- ary a e * S tliat ^ Scania, near Helsingborg, in south- western Sweden, in the three coal-fields of Hoganas,Stabbarp, and R6ddinge. These are situated in the uppermost Triassic or Rhuetic series. At the first, which is the most im portant locality, the strata vary from 100 to 800 feet in thickness, with two seams of coal respectively 1 and 4^ feet in thickness. There is a good fire-clay associated with the lower seam, which is extensively worked for fire bricks and pottery, a large proportion of the coal being used on the spot. In the Danish Island of Bornholm similar coal-bearing strata, probably of Liassic age, form a narrow belt along the south and south-west coast, which it is supposed may continue under the alluvial plain of the Baltic into Pomerania. The Coal-fields of the Continent of Europe. The coal-fields of the continent of Europe, though more scattered and dietui bod than those of England, may be simi larly divided into two groups according to tlieir geolo gical structure, the first being those in which the series is complete, the coal measures being symmetrically arranged upon the Carboniferous limestone and Devonian strata. Examples of this structure are afforded by the long line of coal-fields extending through the north of France and Belgium to the Rhine valley on the north side of the Ardennes, and those of the more easterly district of Silesia and of the north of Spain. The remaining and far more numerous European coal-fields are either contained in hollows in crystalline schists, or rest on the older Palaeozoic rocks, e.g., the central and southern French basins, and those of Saxony and Bohemia. Further east, in central and southern Russia, the order observed in Scotland is reproduced, there being a large development of coal in Car boniferous limestone strata, and something of the same kind seems to be probably the case in China. The best developed portions of the Franco-Belgian coal- Franco- field are seen within the territory of Belgium, the westerly extension into France being entirely covered by a" great thickness of newer strata. Commencing at the eastern side, the first field or basin is that of Liege, which extends from the Prussian frontier near Verviers in a S.W. direction for about 45 miles, the greatest breadth being about 9 miles near Li<%e. The principal working points are concentrated on the western edge, where the lower beds rest on the Carboniferous limestone, the eastern portion being partly covered by Cretaceous and Tertiary strata. The number of coal seams is 83, the upper series of 31 being so-called fat coals, suitable for coking and smiths fires; the middle series of 2 1 seams are semi-dry- or flaming coals; and the remainder or lower series of 31 are dry, lean, or semi-anthracitic coals. The upper series, which are the most valued, are found only in a small area near the centre of the basin at Ougre e, near Li6ge. The seams vary from 6 inches to 5^ feet in thickness, the average being barely 3 feet. This order of succession is observed in the whole of the districts along this axis. The same general structure also prevails throughout the strata which have a comparatively small slope on the northern crop, and are very sharply contorted, faulted, or broken along on the south side of the basins. The local terms platteurs and dressants are used to distinguish the flat and steep portions of the coals respectively. The next basin, that of the Sambre, extends for about 30 miles from Namur to Charleroi, the greatest exposed breadth being about 9| miles. The western and a greater part of the northern side are covered by Tertiary strata, which are very heavily watered. At Montceau, near Charleroi, there are 73 seams, which pass through the various conditions of fat, flaming, and dry coals, from above downwards, according to the order already described. The most important development of the coal measures in Belgium is in the basin of Mous, which extends from Mons to Thulin, a length of about 14 miles, with a breadth of about 7 or 8 miles, a large portion of the area being covered by newer strata. The number of known coal seams is 157, out of which number from 117 to 122 are con sidered to be workable, their thicjmess varying generally between 10 and 28 inches, only a very few exceeding 3 feet. These are classified, according to position, into the following groups, which are taken as a standard for the whole of the north of France and Belgium: 1. Upper series (charbon flemi), 47 seams. These, which occur chiefly in the neighbourhood of Mons, are very rich bituminous coals, especially adapted for gasmaking. 2. Hard coal series (charbon dur), 21 seams. These are, in spite of their name, soft caking coals, less rich in volatile matter than the flenu, but excellent for coking purposes. 56 COAL [COAL-FIELDS. 3. Forge coal series, 29 seams. These are chiefly used for smithy purposes and iron works, but the lower mem bers approximate to dry steam coals. 4. Dry or lean coals, 20 to 25 seams, forming the bot tom series. They are of small value, being chiefly used for brick or lime burning. The amount of compression to which, the strata have been subjected in these coal-fields, has caused them to be sharply contorted into zig-zag folds. In the neighbour hood of Mons a single seam may be passed through six times in a pit of 350 yards vertical depth, and the strata, which if flat would be 9 miles broad, are squeezed into a space 7 miles across and about 8200 feet deep to the bottom of the basin. At Charleroi the compression is still greater, a breadth of 8| miles of flat strata being nar rowed to rather less than half that quantity by contortion into 22 zig-zag folds. The thickness of the overlying Tertiary and Cretaceous strata in the neighbourhood of Moris is from 500 to 900 feet; towards the French frontier the thickness is between 200 and 400 feet, and at Valenciennes about 250 feet. At Aniche these overlying measures, or terrains morts, are 400 feet thick, below which the coal measures are found to contain 23 feet of coal in 12 seams. At Anzin, near Denain, there are 18 seams, together 39 feet, which, is about the maximum development in the north of France. This coal-field, which was unknown before 1734, has reached a very high state of production in spite of great difficulties interposed by the water bearing strata covering the coal measures. It extends for about 45 miles, dimi nishing in extent and value to the westward. The struc ture is very similar to that of the Belgian, one of the most remarkable features being the inclined fault called the cran de retour, which brings the lower or dry coal series of the north side against the higher coking coals of the south side, as shown in the section, Plate II. fig. 4. At Hardinghen, near Boulogne, a small patch of disturbed coal strata was formerly worked. These are now supposed to be of the age of the Carboniferous limestone. The coal-fields of central and southern France are mostly small in area and irregular in structure, with at times remarkable single accumulations of coal of enormous thick ness, which do not, however, extend for any distance. The most important basin is that of Saint Etienne and Rive de Gier, south of Lyons, on the right bank of the Rhone. It is of triangular form, about 28 miles long, with a base of 8 miles. The thickness of the three principal seams at the latter place is about 33 feet, but at Saint Etienne there are from 15 to 18 seams, making together about 112 feet in a total depth of measures of about 2500 fe.et. The basin of the Saone et Loire, near Chalons and Autun, is about 25 miles long in a S.W. and N.E. line. At Creusot, on the north crop, the coals, which are in places extremely thick (the main seam averaging 40 feet, but occa sionally swelling out to 130 feet), dip at a high angle below a covering of New Red Sandstone strata, and appear in a modi fied form,bothas regards thickness and position, on the south side at Blanzy. An attempt has been made to prove the continuity of the series in the bottom of the basin by a deep boring, which was, however, abandoned at a depth of over 3000 feet without passing through the overlying strata. At Moutchanin a remarkable seam or mass of coal was found extending for about 650 yards, with a thickness varying from 60 to 200 feet at the surface, which, however, df- minished to one half 60 yards down, and wedged out at 1 40 yards deep. Another coal field of considerable im portance is that of Alais and Grand Combe near Nimes, which is partly covered by Liassic strata, and has a total maximum thickness of 80 feet of coal. In addition to these must be mentioned the anthracitic series of the Alps, which extend along the flanks of that chain from Savoy and the Tarentaise into Styria and Carinthia. They are of small economic importance. The Secondary and Tertiary coals of France are of com paratively small importance. Lignite is worked, among other places, near Dax in the Pyrenees, and at Trets and Fuveau near Marseilles. The coal-fields of Prussia, situated on the extension of Germ; the Franco-Belgian axis, are the two small basins of the Inde and Worm, east of Adelnau, near Stolberg and Esch- vveiler, which are included in single sharply sloped folds of the mountain limestone, and the great Westphalian basin east of the Rhine, in the valley of the Ruhr. The latter, which is one of the most important in Europe, extends for about 30 miles east and west from Essen to Dortmund. The breadth is unknown; the beds are exposed for about 15 miles at the broadest part, but the actual boundaries to the north and north-east are hidden by Creta- taceous rocks. The greatest depth from the surface to the bottom of the basin is probably about 5000 feet. It is divided lengthways by transverse axes of elevation into four principal basins, besides several smaller ones. The total thickness of measures already proved is from 6000 to 8000 feet, with about 130 seams of coal, together about 300 feet thick. These are divided into three series by two bands of barren measures. The thickness of the individual coal seams varies from 8 inches to 7 feet. Seventy -six are considered to be workable, having a combined thickness of 205 feet, and 54 are unworkable, containing 42 feet of coal. The proportion of workable coal to the whole thickness of strata is as 1 to 33. The order of succession as regards quality is similar to that observed in Belgium, the most highly valued gas and coking coals being at the top of the series, and the dry semi-anthracitic seams at the bottom. On the south side of the axis of the Rhenish De vonian strata, which is the high ground known as the Eifel and Hunsruck, carboniferous strata reappear in what is known as the Pfalz-Saarbriicken basin, occupying a rect angular area between Bingen, Donnersberg, Saarbriicken, and Mettlach, about 60 miles long and 20 miles broad, the productive coal measures being restricted to a triangular space of about 175 square miles in the S.W. corner. The Carboniferous limestone is absent, but the thickness of the coal measures is very great, the upper or Ottweiler series measuring from 6500 to 11,700 feet, with about 20 feet of coal in different parts of the district, and the lower or Saarbriicken series from 9000 to 5200 feet, with 82 workable and 142 unworkable coal seams, making a total of about 350 to 400 feet of coal. The greatest thickness of the upper strata is found in those localities where the lower are thinnest, but the total thickness is computed to be about 20,000 feet in the thickest known section. The coals of the lower division are divided into groups by certain well- marked horizons, usually prominent seams, which have this peculiarity that the best coking and gas coals are found ir?, the bottom of the series, and the drier ones at the top, thus reversing the order observed in the basins on the northern slope. The amount of hygroscopic water in the coal is also found to diminish downwards. In the district between the Ems and the Weser, are situated the small coalfields of Ibbenbiiren, on the easterly extension of the Westphalian basin, and the Piesberg, near Osnabriick, which are of true Carboniferous age. Besides these, there is a curious development of coal in the Weal- den strata which extend in a narrow discontinuous band E. andW. for about 150 miles. The coals are or have been worked at Tecklenburg and Borgloh in the Teutoburger Wald, at Biickeburg in Schaumburg, and in the Osterwald south of Hanover. The coal seams are small and of infe rior quality, but are interesting as showing how nearly the OEBMA.NX.J A L Oi conditions prevailing at the time of the older coal measures were repeated over a part of the same area in Cretaceous times. There are traces of thin discontinuous coal-beds in the Wealden strata of Sussex, but nowhere approaching to the extent of those in the Wealden strata of N. Germany. In the low ground north of Halle, small and irregular patches of coal measures are found at Wettin, Lobejun, and Plotz. These are probably the remains of a single coal-field which has been disturbed and broken up at the time of the eruption of a great mass of igneous rocks which is found in a nearly central position between them. The coal measures are also found in the Thiiringer Wald, the Schwarzwald, on the south side of the Harz, and in the Bavarian Oberpfalz, but none of these localities are im portant as centres of production. In Saxony there are two principal coal-fields, the first being that of the Plauens che Grand, near Dresden, which is chiefly interesting for the very disturbed condition of the measures, and the conse quent difficulty in working ; and the other that of Zwickau, which is one of the most important in Europe. It forms an elliptical basin, about 20 miles long, between Zwickau and Chemnitz, and from 6 to 7 miles in maximum breadth, the greater portion being covered by New Red Sandstone strata. The coal measures, which rest upon old argillaceous schists, are about 1700 feet thick at a maximum, containing 12 principal seams of coal, besides several smaller ones. The most important is the so-called soot coal (Russkohle), which at times attains to a thickness of 25 feet. The series is divided by Geinitz into groups, according to the prevailing character of the associated fossil plants, as follows : 1. Zone of Ferns, corresponding to the upper group. 2. Zone of Annularia and Calamites, or middle group. 3. Zone of Sigillaria, or lower group. A fourth, or Sagenaria zone, found in Silesia, corresponding to the culm measures of Devonshire, completes this classi fication. The most important coal-fields of Eastern Europe are those of Silesia. The Carboniferous limestone series and the lowest coal measures or culm strata reappear in these basins, and are associated with numerous valuable mineral deposits, mainly of zinc and lead ore. The coal-field of Lower Silesia and Bohemia forms a basin between Glatz, Waldenburg, Landshiit, and Schatzlar, about 38 miles long and 22 miles broad. The number of seams from 3^ to 5 feet thick is very considerable (from 35 to 50); but it is difficult to trace any one continuously for any great distance, as they are liable to change suddenly in character. The lower seams usually lie at a higher angle than those above them. There does not appear to be any relation between the coking power of the coals and their geological position, and the same seam often varies in quality in neighbouring mines. The upper Silesian coal district extends in several dis connected masses from Mahrisch-Ostrau in Moravia, in a N.W. direction, by Rybnik and Gleiwitz in Prussia, and Myslowitz in Poland, being held partly by Austria, Prussia, and Russia, the Prussian portion between Zrabze and Myslowitz being the most important, extending over 20 miles in length, by nearly 15 in breadth. The greatest thickness of coal in workable seams (from2|- to GO feet thick) is estimated at a total of 333 feet, the thickness of the measures beingabout 10,000 feet. A very large proportion of this coal-field is hidden by New Red and Cretaceous strata. The Tertiary coals or lignites of Germany are of consider able importance, being distributed over large areas, the seams often attaining a great thickness, although rarely continuous for any great distance. The principal deposits are situated in the lower parts of the valleys of the Rhine and the Elbe, in Nassau, and in the high ground of the Rhon in Bavaria. The lignite district of the Rhine ex tends from near Bonn down to Deutz and Bensberg below Cologne. The pigment known as Cologne earth is a sepia- coloured lignite, which can be ground to a fine powder when dried. In Nassau the so-called bituminous wood, a variety of lignite containing flattened masses of wood of a light brown colour, is very common. The produce of these districts is mainly consumed for house fuel and steam boilers, some small quantity having been used for the pro duction of paraffin and photogen oil. The coal-fields of the empire of Austria-Hungary are of Austria. very considerable interest, from the great diversity in their geological position. Coals of Carboniferous age are mainly confined to the northern provinces of Bohemia, Moravia, and Silesia ; but in Hungary and the Alpine- lands, especially in Styria, coals of Tertiary age are found, which approach very closely in composition and quality to those of the coal measures. First in importance among the former class, is the basin of Pilsen in Bohemia, which covers an area of about 300 square miles. It rests upon Silurian shale, and is covered unconformably by Permian conglomerate and sand stone. The coals vary considerably in different localities ; the total thickness of the workable seams, from 3 to 5 in number, does not exceed 20 feet. There is a remarkable bed of slaty cannel in the upper part of the series, which contains animal remains of Permian types associated with the ordinary coal flora. Another important basin, that of Schlan-Kladno, E. of Prague, appears along the north edge of the Silurian strata, extending for about 35 miles E. and W. At Kladno, where it is best developed, it contains two principal seams, of which the upper is from 10 to 20 feet, and the lower or main seam from 19 to 40 feet thick. At Rossitz, near Briinn, in Moravia, a belt of coal measure, resting upon crystalline rocks, has been consider ably worked. There are three seams, together from 27 to 30 feet thick. These beds are said to be the equivalent of the upper seams of Pilsen and Kladno. In Moravia, Silesia, and Poland the coal measures are associated with the mountain limestone, which in Central Germany, east of Westphalia, is generally absent. The upper Silesian coal-field is situated in Prussia, Austria, Sile sia, and Russian Poland, the largest portion being in the first country. The area of this basin is about 1700 square miles, a considerable portion of it being hidden by Secondary and Tertiary strata. In the Austrian portion at Ostrau in Moravia there are 370 seams, of which 117 are workable, with a thickness of about 350 feet of coal. The largest seams are situated in the upper series, the principal one being about 13 feet thick. The coals of the neighbour hood of Ostrau are very full of gas, which occasionally finds its way into the cellars of the houses in the tow r n, besides giving off large quantities of fire damp in the workings. A bore hole put down 150 feet to a seam of coal in 1852, gave off a stream of gas which was ignited at the surface, and has continued to burn, with a flame many feet in length, to the present time. The same coal-field extends into the district of Cracow, where it contains numerous seams of great thickness, which, however, have been but partially explored. In the Austrian Alps anthracitic coals occur at various points along the northern slopes, in strata of the age of the culm measures, but nowhere in any great quan tity. In the Carpathian countries true coal measures are not largely developed, the principal locality being near Reschitza in the Banat, where 4 seams, from 3 to 10 feet in thickness, are worked to a certain extent. At Steyerdorf, near Oravicza on the Danube, a remark able coal-field is found in the Lias. There arc 5 seams, from 3 to 7 feet in thickness, which are bent into an anticlinal, besides being disturbed by numerous faults. The coal is of a very good quality, yielding a coke suitable for V. S 58 GOAL [COAL-FIELDS iron-smelting. The annual production is about 260,000 tons. Similar coals occur in the Lias at Dreukowa, and near Fiinfkirchen, where there are 25 workable seams, together about 80 feet thick, also of a good coking quality, but very tender in working, making a great deal of slack. Secondary coals occur in the Trias and Oolitic strata at various points in the Alps, but are only of local interest. In the Gosau strata belonging to the chalk, coaL is worked at various points in the Alpine lands, the average annual production being about 25, 000 tons. Eocene coals occur in Dalmatia, and Miocene lignite in the Vienna basin in Southern Moravia, one seam, about 10 feet thick, cover ing an area of about 120 square miles. In the Styria-Hun- garian Tertiary basin, Tertiary coals are developed on a very great scale, especially in Styria, at Salgo Tarjan in N. Hungary, and in the depression between the Matra and the crystalline rocks of Upper Hungary. These localities represent only those best known by workings, many more being undeveloped. The lignite beds are often of great thickness, e.g., 70 feet at Hrastuigg, and 130 feet at Trifail. The production of Tertiary coal in Styria is about 500,000 tons annually. At Leoben and Fohnsdorf, lignites are worked of a quality closely approaching to that of Carboni ferous coal, and are largely consumed in the production of iron and steel, having almost entirely replaced charcoal in the local forges. In Bohemia, Miocene brown coal strata cover a very large area, the principal basins being those of Eger, Carlsbad, and Teplitz, together about COO square miles, the main seam occasionally attaining a thickness of over 100 feet, The trade in this coal is very considerable along the entire valley of the Elbe. The coal-fields of Russia have been but imperfectly known until a comparatively recent period, when the de mand for fuel caused by the extension of railways and the increase in manufacturing industries has stimulated ex plorations, which have resulted in the discovery of coal- bearing strata of considerable magnitude and extent. These belong to the period of the Carboniferous limestone, like the lower coals of Scotland. In Central Russia the coal-bearing area belonging to the Carboniferous limestone is said to cover about 13,000 square miles, the centre of the basin being at Tula, S. of Moscow. There are two principal seams, 3 ft. G in. and 7 feet thick, in the bottom of the series near the top of the Old Red Sandstone. The coal is of inferior quality, con taining about 12 to 16 per cent, of ash, and from 2 to 5 per cent, of sulphur. In Southern Russia, between the river Donetz and the head of the sea of Azoff, a more important coal-field occurs, also in the Carboniferous limestone, covering an area. of 11,000 square miles. There are sixty seams of coal, forty- four being workable, with a total thickness of 114 feet. The best is a dry or semi-anthracitic coal, resembling that of South Wales. At Lugan and Lissitchia Balka, a thick ness of 30 feet of coal is found in 900 feet of strata. In the Ural, coal is found in sandstones, iuterstratified in the Carboniferous limestone in the district north of Perm, between the parallels of 57 and 60 N. latitude. The strata dip at a high angle to the west, under the Permian strata. The thickest coals are at Lithwinsk at the northern end, where there are three seams worked, measuring from 30 to 40 feet each ; further south they become thinner. The coals appear to be similar in quality to those of the central coal-field. In Poland, about Bendzin and Lagorze, N. of Myslo- witz, an extension of the Upper Silesian coal-field covers an area of about 80 square miles, being partly covered by Permian strata. Nine seams of coal are known, varying from 3 to 20 feet in thickness ; but they do not occur to gether, except in a small part of the centre of the basm. The aggregate thickness of coal is about 60 feet. This is the only district in which true coal measure strata are found in European Russia. Among the southern countries of Europe, the first place Span must be given to the coal-fields of Spain, but even these are of comparatively small importance, when measured by a northern standard, consisting of a few small and scattered basins, in which both Carboniferous and Secondary coals are represented. The Carboniferous limestone acquires a con siderable development in the Cantabrian chain along the north coast, and is associated with overlying coal measures near Oviedo and Leon. In the former area the coals are often considerably disturbed, becoming anthracitic at the same time. The best seams are from 5 to 8 feet thick. In the Satero valley near Sotillo, N.E, of Leon, a seam called El Carmen, averaging 60 feet, is sometimes 100 feet thick, and is said to be in places associated with another which is occasionally 180 feet thick. Another basin of importance is that of Belmez and Espiel, occupying a narrow valley iu older Palajozoic strata, about 20 miles north of Cordova, which has recently been traversed by a railway connecting it with the main lines from Lisbon and Cadiz. This pro duces coking and gas coals of good quality, which are in considerable demand for smelting in the lead and other mineral districts in the neighbourhood. The other principal localities are at Villaneuva del Rio near Seville, and San Juan de la Abaderas in Catalonia. Coals of Neocomian age are found at Montalban, in the province of Teruel, and lignites of Miocene age, among other places, at Alcoy in Valencia, and Galas in Catalonia. In Portugal a small tract of lower Carboniferous strata, Portuga containing anthracite, occurs at San Pedro de Cova, near Coimbra, but the produce is very small. In Italy there is very little Carboniferous coal, what does Italy. occur being mainly of an anthracitic character in very dis turbed strata in the Piedmontese Alps. Tertiary lignites are worked at several places in Tuscany and in Naples, but the total output is inconsiderable when measured by the standards of more northern countries. Extra-European Coal-fields. In Turkey, Carboniferous coal is found at Heraclea in Turkey. Asia Minor, and has been worked from time to time, but hitherto without much influence upon the coal produce of Europe. Lignites are known to occur near Smyrna, and in the Lebanon and various other points in Syria. It is doubtful whether any Carboniferous coal exists in Africa. Africa. Coal-bearing strata, probably of the age of the New Red Sandstone, the so-called Karoo beds, cover a con siderable area, both in the Cape Colony and Natal, but little is known of the details of the coal-beds beyond state ments of the excellence of the quality of the coals. Lig nite occurs in the high lands of Abyssinia, and probably at numerous other points in the interior. The coal-bearing strata of India occur in numerous de- India, tached basins, which are widely distributed over the whole peninsula, their aggregate area, however, being but small. The principal development is in the valley of the Damodar river, one of the southern tributaries of the Hugli, the largest coal field being that of Raniganj, on the line of th a East Indian Railway, about 140 miles W. of Calcutta, wluch covers an area of about 500 square miles. It is a basin resting upon crystalline schists, and partly covered by Triassic sandstones iu the centre, and by jungle and alluvium, to the eastward, so that the real area is not yet known. The strata are divisible into three series as follows : Upper or Raniganj series coal-bearing. Middle or Ironstone series no coals. Lower or Barrakur series coal-bearing. 5IA.] C A L 59 The total thickness may be from 3000 to 4000 feet ; the ironstone series is a group of shales containing nodular ironstone about 1500 feet thick, but diminishing westward. Numerous coal seams are worked at different points, but they cannot be traced continuously for more than a short distance without change. In the upper series an average of 11 seams/ together about 120 feet thick, are known in the eastern or Raniganj district, and 13 seams, together 100 feet, on the western side. Occasionally single seams acquire a great thickness (from 20 to 80 feet), but the average of those worked locally is from 12 to 18 feet. In the lower series, 4 seams, together G9 feet, are known. The coals are generally of inferior quality, containing a con siderable amount of ash, and are non-coking in character. The coals of the lower series are better, yielding fairly good coking and gas coal at Sanktoria, near the Barrakur River. A small coal-field at Kurhurbali, near Luckeeserai, on the East Indian Railway, has recently been developed to a considerable extent for locomotive purposes. It covers about 1 1 square miles, with an aggregate of 3 seams, vary ing from 9 to 33 feet in thickness. They are of better quality than those of any other Indian cool-field at present known, and are of great value to the railway, which is now supplied with fuel at a lower rate than probably any other railway company in the world. There are several other coal-fields in Bengal, especially that at Jherria, near the sacred mountain of Parisnath, those south of Hazaribagh, and those on the Sone River, but none are as yet developed to any extent, being away from the great lines of communication. On the western side of India the principal workings are at Mopani, on the Nerbudda, on the line of the Great Indian Peninsular Rail way, the coal being used by the railway. It is of inferior quality, and the strata are inclined at a considerable angle, rendering the working difficult. _ In the Central Provinces a new coal-field of considerable extent has been recently discovered, almost entirely by boring, on the Wardha and Chanda districts, on the upper tributaries of the Godaveri, a considerable portion being within the Nizam s province of Berar. It is probable that this may become one of the most important sources of coal supply for Central and Western India, but no great amount of work has as yet been done upon it. Besides the above, there are several other known coal fields, for details of which the reader is referred to the Reports of the Geological Society of India. The age of the Indian coals is generally supposed to be Permian, the only fossils that have been found in them being plants which are referred to Permian types in Europe. If, however, the overlying sandstones, containing reptilian fossils, generally reputed to be of Triassic age, should, as seems likely, prove to be Permian, it is not improbable that the coal-bearing strata may actually belong to the period of the upper coal measures, and the Indian coal-fields would then be strictly analogous to the deep irregular basins of Southern France and Central Europe, with which they have many structural points in common. No marine strata, or anything approximating to the char acter of the Carboniferous limestone, are known anywhere on the plains of India, although they are found in the salt range of the Punjab and in the Himalayas. The coal-fields of China are known, from the researches of Baron von Richthofen, Prof. Pumpelly, and other travellers, to cover a very large area, comparable only with those of North America; but, as may be imagined, no very detailed information has as yet been obtained concerning them. According to the first-named authority, there are no newer formations than the Trias in China other than alluvial deposits of enormous thickness, but Palaeozoic strata, from the Silurian Howards, are developed on a very large scale. Coal of Carboniferous age exists in Manchuria, mostly in inaccessible mountain valleys, and further west all along the Great Wall. Near Peking there are beds 95 feet thick, which supply the city with fuel. The most extensive development is to the west and north-west, on the south of the great mountain range which stretches across Western China, where there is an area of Carboni ferous strata of 100,000 square miles. The great plain of China is bounded by a limestone escarpment from 2000 to 3000 feet high, which is capped by a plateau covered by 30,000 square miles of coal measures, in which the coal seams, 30 feet thick, lie perfectly hori zontal for 200 miles, and are reported to extend beyond the frontier into Mongolia. Most of the localities are, how ever, far in the interior. The coal of Shantung, though not near good harbours, is the most accessible of all Chinese coal from the sea. It also occurs in the other maritime provinces, but in districts offering fewer facilities for export. It is obvious, from the enormous dimensions given to these coal-fields, that it will be a long time before anything like a moderately accurate estimate of their value can be obtained. In Japan coal is worked at several points, but no detailed Japan account of the mode of its occurrence has been published. At the island of Takasima, near Nagasaki, a colliery is worked by the Japanese Government for the supply of their steamers on a tolerably large scale. In the great islands of the Indian and South Pacific Oceans, coal-bearing strata are known at many different points ; but in the absence of systematic investigation, no general estimate can be formed of their position, extent, or value. In the Dutch settlements, coal has been found in Sumatra and Borneo, the best known deposit being that of Borneo. Pengaron, on the south-east of the latter island, where a mine has bsen worked by the Dutch authorities for several years. The section of the strata, as proved by a level, shows a series of 15 seams above 1 foot in thickness, together about 36 feet, in about 520 feet of measures, 6 of these having been worked. The best appear to be somewhat similar to the steam coal of the North of England. In the British settlement of Labuan, off the north coast of Borneo, 5 Labuan. workable seams, together about 27 feet thick, are estimated to cover the whole island. This is probably of Tertiary age, but approximates in composition to many of the non- coking coals of the coal measures. The Labuan coal is also remarkable for containing large masses of fossil resin. The most important southern coal deposits, however, are Australia those of Australia, which extend, with short intervals, from the Gulf of Carpentaria to Bass s Straits. In the northern districts, the distribution appears to be somewhat similar to that seen in South America, Secondary and Tertiary basins occupying the ground near the sea, while true Carboniferous coal is found further inland; but in New South Wales, where their development is greatest, older coal-bearing strata extend along the eastern slope of the continent, be tween the parallels of 29 and 35 degrees S. latitude, covering a very large area in several detached portions, the largest probably exceeding 12,000 miles, and come down to the sea. The principal workings are situated near Newcastle, at the mouth of the Hunter River, at Wollongong, 60 miles south of Sydney, and at Hartley, about 90 miles inland. The coal seams vary from 3 to 30 feet in thickness Li the Newcastle district, 16 seams above three feet thick being known. The coals are mainly of a free-burning class, but some are bituminous, giving a good coke. In the upper most part of the series oil shales and cannel are found. The age of the Australian coal measures has been the subject of considerable controversy. Formerly it was supposed that they were Oolitic, from the supposed affinities of the fossil plants ; but it has since been shown that the coal -bearing COAL [COAL. FIELDS. portions of the series are interstratifiecl with marine strata, containing fossils of Carboniferous and Devonian types. The same association is observed in the coal series of Bowen River in Queensland, and on those of the Mersey River in Tasmania, showing the extension of the Carboniferous strata in a chain of detached basins from the 20th to the 40th parallel of S. lat, or about 1400 miles. In Queensland the strata are estimated to cover an area of 24,000 square miles, without taking into account possible extension under the Cretaceous strata of the interior. Up to the present time, however, very little has been done towards their develop ment, the districts in which they occur being too far from the settled portions of the country. The principal mines now open are on newer strata of Cretaceous age nearer the sea, at Ipswich, in the neighbourhood of Brisbane. Some of these coals are remarkably like those of South Durham, and yield a good hard coke, suitable for blast-furnace purposes. New Zea- True coal measures are not known to exist in New Zea land- land, but coal-bearing strata of two different periods have been described by Dr Hector, Dr Haast, Captain Hutton, and other geologists. The newer series yield a lignite, which is described in the reports as hydrous coal ; while the older, which is probably of Cretaceous or Jurassic age, yields a superior class of combustible, known as anhydrous coal. These minerals occur at many different points in the two larger islands, and although no systematic detailed account of them is as yet available, a considerable amount of information on this subject is contained in the various geolo gical reports published by the New Zealand surveyors. North In North America, the Carboniferous strata are divided America, by geologists into two principal groups, the lower or sub-Carboniferous, which correspond to the Carboniferous limestone of Europe, and the Carboniferous, which includes the millstone grit and coal measures. The first of these is about 5000 feet thick in Penn sylvania, consisting mainly of shales and sandstones ; but in the Mississippi valley, in Illinois, Iowa, and Missouri, a considerable thickness of limestone is developed in this part of the series. In the former region some thin coal seams are found, the relation between the two areas being in this respect similar to that of the Carboniferous lime stone in England to the coal-bearing formations of similar age in Scotland. The millstone grit forms a mass of sandstones and conglomerates from 1200 to 1400 feet thick in Eastern Pennsylvania, but thins rapidly to the westward, being only from 100 to 250 feet thick in Ohio and Tennessee. In Arkansas, the compact siliceous rock known as novaculite, or Arkansas hone stone, occurs in this member of the Car boniferous series. The coal measures proper cover a very large area, both in the United States and in Canada. First in importance is the Appalachian coal-field, covering about 60,000 square miles, extending through parts of Pennsylvania, Ohio, Virginia, eastern Kentucky, Tennessee, and Alabama. The maximum thickness of strata is from 2500 to 3000 feet ; that of included coal is 120 feet near Pottsville, G2 feet at Wilkesbarre, and about 25 feet at Pittsburg, showin" a gradual diminution to the westward. The most persistent coal is the Pittsburg seam, which is known over an area measuring 225 miles by 100 miles, but with a thickness varying from 2 to 1 4 feet. The anthracite district of central Pennsylvania occupies an area of about G50 miles on the left bank of the Susque- hanna River. The strata between Pottsville and Wyo ming, which belong to the lowest portion of the coal measures, are probably about 3000 feet thick, but it is difficult to arrive at an exact estimate, owing to the numerous folds and contortions. There are from ten to twelve seams above 3 feet in thickness ; the principal one, known as the Mammoth or Baltimore vein, is 29-| feet thick at Wilkesbarre, and in places even exceeds 60 feet. The Illinois and Missouri basin covers a considerable part of these States, as well as of Indiana and Kentucky, Iowa, Kansas, and Arkansas. Its area is estimated at 60,000 square miles, the thickness varying from 600 feet in Missouri to 3000 feet in western Kentucky. The aggregate thickness of coal is about 70 feet. A good furnace coal is obtained in Indiana, the so-called block coal of Brazil near Ind ianopolis, which, like the splint coals of Scotland and those of Staffordshire, can be used in the blast furnace without coking. In Michigan a nearly circular area of coal measures, of about 5000 square miles, occurs in the lower peninsula between lakes Huron and Erie. The thickness is only 120 feet, and the coals unimportant. Other coal-bearing areas of less value are known in Texas and Rhode Island. The Carboniferous strata are largely developed in the eastern provinces of the Dominion of Canada, notably ic New Brunswick and Nova Scotia. The lower Carbonifer ous group here consists of about 6000 feet of red sand stones and green marls, with thick beds of fossiliferous limestones, accompanied by gypsum. The limestones in crease in thickness southward. In this series occurs the peculiar pitch-like or asphaltic coal of the Albert mine in New Brunswick, of which an analysis is given in Table I., supra. The overlying coal measures, including the mill stone grit, occupy an area estimated at 18,000 square miles. The whole thickness of this group at South, Joggins is about 14,750 feet, with 76 included coal seams, together 45 feet in thickness, which are contained in the middle division of the series. At Pictou there are six seams, together measuring 80 feet in thickness. The coal measures in this area approach more near to the great coal fields of Europe in thickness than those of the other American Carboniferous districts. Rocks of Carboniferous age occur in various places on both flanks of the Rocky Mountains, and in the Arctic Archipelago, but have not yet been explored. Lignite-bearing strata of Cretaceous and Tertiary age occupy a very considerable area in the central and western portions of North America, especially in the upper Missouri and Saskatchewan valleys, in Utah and Texas, and in California, Oregon, and Vancouver Island. In the last locality coal has been extensively mined near Nanaimo, on the east coast, for several years past, in strata of Cretaceous age. Tertiary lignites are worked in Belling- ham Bay, at Goose Bay in Oregon, and at Monte Diabolo, near San Francisco. The lignitic formations of the eastern flank of the Rocky Mountains, which are considered by Hayden to occupy a position between the Cretaceous and Eocene Tertiary strata, occupy an area estimated at about 50,000 square miles within the United States, and extend both northward into Canada and southward into Mexico. In South America coal, probably of Carboniferous age, South is found in the Brazilian provinces of Sao Pedro, Rio Americ Grande do Sul, and Santa Catharina, and in the neighbouring state of Uraguay. The largest area is that known as the Candiota coal-field, which is exposed for about 50 miles in the valley of the river of the same name. The sections ex posed show 5 seams from 9 to 25 feet each, or together about 65 feet of coal. Other basins are known at S. Sepe" and S. Jeronimo, on the Jacahahay River. The latter is the only point at which mines are worked, as the coals, though thinner than those of the other localities mentioned, are situated within the reach of navigable waters, having only to bear a land carriage of 8 miles to the river. MINING. 1 COAL Cl On the west coast of South America, Cretaceous coals are worked at Lota, iu Chili, and at Sandy Point, in the Straits of Magellan. In Peru both Secondary and Carboni ferous coals are known at various points in the interior, the former occupying a position on the first rise of the table land of the Andes, while the latter occur in higher ground, at a greater distance from the coast. Good coal is also found at many points in the Santa valley. Much of the Peruvian coal has undergone considerable disturbance and metamorphism subsequent to its deposi tion. At Porton, 45 miles east of Truxillo, a ridge of coal-bearing sandstones has been changed into a hard quartzite, with an interstratified seam of anthracite in a nearly vertical position. The coal is remarkable as con taining a large amount of sulphur (see analysis Table I.). The hitherto inaccessible position of these places, which are usually more than 10,000 feet above the sea-level, has prevented the development of coal-mining in Peru ; but the extension of railways into the mountains will probably bring them into importance, by stimulating a local demand for fuel. Extent of existing Workable Coal. The following summary of the amount of coal estimated as workable remaining in the different districts, which is taken from the report of the Royal Commission on coal, and founded upon investigations made in the years 18G6-71, furnishes an approximate measure of the comparative value, present and prospective, of the different coal-fields of the United Kingdom. The quantities represent the probable aggregate yield of all seams above 1 foot thick. Coal-Fields. Within 4000 feet. Tons. Coal remaining in exposed Coal-fields. Below 4000 feet. Tons. 32,456,208,913 4,109,987,004 265,000,000 4,218,970,762 1,885,340,220 South Wales, Forest of Dean, Somersetshire, South Staffordshire, Shropshire, f Forest of Wy re f Clee Hills, ) Leicestershire Warwickshire, North Wales, Anglesea, North Staffordshire, Yorkshire and Derbyshire, Yorkshire (Oolitic, &c.) ... Lancashire and Cheshire, . Northumberland and Durham, Cumberland, Scotland, do (Oolitic), Ireland, 1,906,119,768 836,798,734 458,652,714 2,005,000,000 5,000,000 3,825,488,105 18,172,071,433 70,000,000 5,546,000,000 10,036,660,236 405,203,792 9,839,965,930 3,500,000 155,600,000 1,000,785,488 234,728,010 90,000,000 90,206,240,387 7,320,840,722 The quantity estimated as lying above the workable limit of 4000 feet under the Permian and other formations, in the central and northern counties of England, is 56,248,000,000 tons, covering an area of 2044 square miles, in addition to which, in the flat ground between the Mersey, Denbigh shire, the North Staffordshire hills, Cannock Chase, and Colebrookdule, a further area of 843 square miles at inac cessible depths is computed to contain Between 4000 and 6000 feet, 29,341,649,067 tons. 6000 ,, 10000 15,302,741,333 ,, 41,144,300,400 , Adding to this the amount below 4000 feet from the previous table, 7,320,840,722 ,, Total unavailable coal, 48,465,141,122 ,, As compared with 146,454,240,387 ,, the quantity of workable coal, as made up of the two amounts, 90,200,240,387 and 56,248,000,000 tons, given above. From this it follows that, out of the probable total quantity of coal in the P>ritish coal measures, rather more than three-fourths may become available for consumption, or about 1170 times the amount of the present annual out put of 125 million tons. Similar estimates have been formed for the coal-fields of other countries, especially in France and Germany, but it is doubtful whether the necessary structural details are sufficiently well known to admit of more than a tolerably rough guess being made. COAL-MINING. The opening and laying out, or, as it is generally called, Prelimin- " winning," of new collieries is rarely undertaken without a ary trial preliminary examination of the character of the strata by coal-work means of borings, either for the purpose of determining ings the number and nature of the coal-seams in new ground, or the position of the particular seam or seams which it is proposed to work in extensions of known coal-fields. A/.3 N.4 The principle of proving a mineral field by boring is illustrated by figure 3, which represents a line direct from the dip to the rise of the field, the inclination of the strata being one in eight. No. 1 bore is commenced at the dip, and reaches a seam of coal A, at 40 fathoms ; at this depth it is considered proper to remove nearer to the outcrop, so that lower strata may be bored into at a less depth, and a second bore is commenced. To find the position of No. 2, so as to form a continuous section, it is necessary to reckon the inclination of the strata, which is 1 in 8 : and as bore No. 1 was 40 fathoms in depth, we multiply the depth by the rate of inclination, 40 x 8 = 320 fathoms, which gives the point at which the coal seam A should reach the surface. But there is generally a certain depth of alluvial cover which requires to be deducted, and which we call 3 fathoms, then (40 - 3 = 37) x 8 = 296 fathoms ; or say 286 fathoms is the distance that the second bore should be placed to the rise of the first, so as to have for certain the seam of coal A in clear connection with the seam of coal B. In bove No. 3, where the seam B, according to the same system of arrangement, should have been found at or near the surface, another seam C is proved at a considerable depth, differing in character and thickness from either of the preceding. This derangement being carefully noted, another bore to the outcrop on the same principle is put down for the purpose of proving the seam C ; the nature of the strata at first is found to agree with the latter part of that bored through in No. 3, but immediately on crossing the dislocation seen in the figure it is changed, and the deeper seam D is found. The evidence therefore of these bores (3 and 4) indicates some material derangement, which is then proved by other bores, either towards the dip or the outcrop, according to the judgment of the borer, so as to ascertain the best position for sinking pits. The methods of boring are similar to those adopted for Methods of deep wells, or in other departments of mining. For shal- boring. U O A L [MINING. low bores, the boring is generally with wrought iron rods screwed together in lengths, armed with a cutting chisel and workin^ by percussion, the tool being lifted by hand and allowed to fall with its full weight upon the rock. The pounded material is removed at intervals, by substi tuting a shell pump or tube with valves at the bottom, whose action is similar to that of the foot valves of an ordinary lifting pump. The sludge brought to the sur face indicates the nature of the ground passed through. In very deep borings, however, the use of rigid rods and fixed tools is found to present two serious evils, namely, the excessive weight on the tool caused by the increased length of the rods, and the great length of time required to withdraw the tool and remove the detritus. The first of these difficulties has been overcome by the _use of the free falling cutters, where the tool, instead of being attached rigidly to" the rod, moves in a guide-block in such a manner as to be lifted with the rods, falling freely when the top of the stroke is reached. The rods, when lowered, pick up the tool at the bottom of the hole in readiness for the next lift. By this means the momentum of the tool is kept constant whatever may be the weight of rods employed. The use of a wire rope winding on a drum, instead of rods for suspending the boring tool, allows the latter to be withdrawn and replaced with much greater rapidity than can be done with rods. This method has been very successfully adopted by Messrs Mather & Platt of Salford. But perhaps the best methods of expeditious boring are those (Fauvelle s) whereby the detritus is removed as it forms by con tinuously flushing out the hole with water, hollow rods being used down which the water flows while it rises through the annular space between the rod and the lining tube of the bore hole. This has the advantage of giving a clear surface for the tool to cut on, instead of its having to work through its own sludge, as is the case when the shell pump is only used at intervals. Of late years the value of boring for exploratory purposes has been much increased by the adoption of tubular or crown borers, which cut out an annu lar groove, leaving a core of unbroken rock in the centre, which is then brought out by a grapnel in a solid piece. One of. the m^st successful of these methods is that due to Leschot of Geneva, where a rotating cutter, armed with amorphous black diamond, the hardest known substance, is used, the detritus being continuously removed by water on Fauvelle s plan. The machinery adopted for this pur pose, as modified by Messrs Beaumont & Appleby. has been employed with great success to bore holes exceeding 2000 feet in depth. Methods of The working of coal may be conducted either by means working, of levels or galleries driven from the outcrop in a valley, or by shafts or pits sunk from the surface. In the early days of coal mining, open working, or quarrying from the out crop of the seams, was practised to a considerable extent ; but there are now few if any places in England where this can be done. In 1873 there could be seen, in the thick coal seams of Bengal, near Raniganj, a seam about 50 feet thick laid bare, over an area of several acres, by stripping off a superficial covering varying from 10 to 30 feet, in order to remove the whole of tbe coal without loss by pillars. Such a case, however, is quite exceptional. The operations by which the coal is reached and laid out for removal are known as "winning," the actual working or extraction of the coal being termed "getting." In the accompanying figure, No. 4, A B is a cross cut-level, by which the seams of coal 1 and 2 are won, and C D a ver tical shaft by which the seams 1, 2, and 3 are won. When the field is won by the former method, the coal lying above the level is said to be " level-free." The mode of winning by level is of less general application than that by shafts as the capacity for production is less, owing to the smaller size of roadways by which the coal must be brought to the Fig. 4. surface, levels of large section being expensive and difficult to keep open when the mine has been for some time at work. Shafts, on the other hand, may be made of almost any capacity, owing to the high speed in drawing which is attainable with proper mechanism, and allow of the use of more perfect arrangements at the surface than can usually bo adopted at the mouth of a level on a hill side. A more cogent reason, however, is to be found in the fact that the principal coal-fields are in flat countries, and where the coal can only be reached by vertical sinking. The methods adopted in driving levels for collieries are generally similar to those adopted in other mines. The ground is secured by timbering, or more usually by arching in masonry or brick- work. Levels like that in fig. 4, which are driven across the stratification, or generally anywhere not in coal, are known as " stone drifts." The sinking of colliery shafts, however, differs considerably from that of other mines, owing to their generally large size, and the difficulties that are often encountered from water during the sink in sc. The O O actual coal measure strata, consisting mainly of shales and clays, are generally impervious to water, but when strata of a permeable character are sunk through, such as the magnesian limestone of the north of England, the Permian sandstones of the central countries, or the chalk and greensand in the north of France and Westphalia, special methods are required in order to pass the water bearing beds, and to protect the shaft and workings from the influx of water subsequently. Of these methods one of the chief is the plan of tubbing, or lining the excava tion with an impermeable casing of wood or iron, gene rally the latter, which is built up in segments forming rings, that are piled upon each other throughout the whole depth of the water-bearing strata. This method necessitates the use of very considerable pumping power during the sinking, as the water has to be kept down in order to allow the sinkers to reach a water-tight stratum upon which the foundation of the tubbing can be placed. This consists in a heavy cast-iron ring, known as a wedging crib, or curb, also fitted together in segments, which is lodged in a square-edged groove cut for its recep tion, tightly caulked with moss, and wedged into posi tion. Upon this the tubbing is built up in segments, usually from 10 to 12 being required for the entire cir cumference, the edges being made perfectly true. The thickness varies according to the pressure expected, but may be taken at from f to 1| inches. The inner face is smooth, but the back is strengthened with angle brackets at the corners. A small hole is left in the centre of each segment, which is kept open during the fitting to prevent undue pressure upon any one, but is stopped as soon as the circle is completed. In the north of France and Belgium wooden tubbings, built of polygonal rings, were at one time in gc.ieral use. The polygons adopted were of 20 or more sides approximating to a circular form. The second principal method of sinking through water bearing ground is that which was first adopted by M. Sinking shafts . Pnenma- sinking. MIXING. C A L Trigor, in France, and has also been used by civil engineers in putting down deep foundations for bridge piers, namely, by compressed air. The shaft is lined with a cylinder of "wrought iron, within which a tubular cham ber, provided with doors above and below, known as an air-lock, is fitted by a telescopic joint, which is tightly packed so as to close the top of the shaft air-tight. Air is then forced into the inclosed space by means of a compressing engine, until the pressure is sufficient to oppose the flow of water into the excavation, and to drive out any that may collect in the bottom of the shaft through a pipe which is carried through the air-sluice to the surface. The miners work in the bottom in the same manner as divers in an - ordinary diving-bell. Access to the surface is obtained through the double doors of the air sluice, the pres sure being reduced to that of the external atmosphere when it is desired to open the upper door, and increased to that of the working space below when it is intended to communicate with the sinkers, or to raise the stuff broken in the bottom. This method has been adopted in various sinkings on the Continent. At Bracquenie, near Mons, the miners worked in an atmosphere up to 45 !b pressure on the square inch, without experiencing any great difficulty, but they were found to be more susceptible to pulmonary disorder upon changes of weather than those who worked under the ordinary conditions of pressure. The third method of sinking through water-bearing strata is that of boring, adopted by Messrs Kind & Chau- dron in Belgium and Germany. For this purpose a horizon tal bar armed with vertical cutting chisels is used, which cuts out the whole section of the shaft simultaneously. In the first instance, a smaller cutting frame is used, boring a hole from 3 to 5 feet in diameter, which is kept some 50 or GO feet in advance, so as to receive the detritus, which is removed by a shell pump of large size. The large trepan or cutter weighs about 16 tons, and cuts a hole of from 9 to 15 feet in diameter. The water-tight lining may be either a wrought iron tube, which is pressed down by jack screws as the bore hole advances, or cast-iron tubbing put together in short complete rings, in contradistinction to the old plan of building them up of segments. The tubbing, which is considerably less in diameter than the bore hole, is suspended by rods from the surface until a bed suitable for a foundation is reached, upon which a sliding length of tube, known as the moss box, bearing a shoulder, which is filled with dried moss, is placed. The whole weight of the tubbing is made to bear on the moss, which squeezes outwards, forming a completely water-tight joint. The interval between the back of the tubbing and the sides of the bore hole is then filled up with concrete, which on setting fixes the tubbing firmly in position. The introduction of these special methods has consider ably simplified the problem of sinking through water-bear ing strata. Some of the earlier sinkings of this kind, when pumps had to be depended on for keeping down the water, were conducted at great cost, as, for instance, at South Hetton, and more recently Ryhope, near Sunderland, through the magnesian limestone of Durham. The size and form of colliery shafts varies in different dis tricts, but the tendency is now generally to make them round, and from 12 to 15 feet in diameter. In the Midland counties, from 7 to 9 feet is a very common size, but larger dimensions are adopted where a large production is re quired. At Bagillt, on the Dee, a shaft of 22 feet in diameter was commenced a few years ago, but was reduced in diameter a short distance down. Since the accident at Hartley colliery, caused by the breaking of the pumping engine beam, which fell into the shaft and blocked it up, whereby the whole company of men in the mine were starved to death it has been made compulsory upon mine owners to have two pits for each working, in place of the single one divided by walls or brattices which was formerly thought sufficient. Ths use of two indepen dent connections whether separate pits or sections of the same pit, between the surface and the workings is neces sary for the service of the ventilation, fresh air from the surface being carried down one, known as the " downcast," while the foul or return air of the mine rises through the other or " upcast" pit back to the surface. Where the mine is heavily watered, it is often necessary to establish a special engine pit, with pumps permanently fixed, or a division of one of the pits may be devoted to this purpose. The use of direct-acting high-pressure pumping engines placed at the bottom of the shaft has become common during the last ten years. They have the advantage of doing away with the heavy reciprocating rod from the engine at the surface, and may be worked either by steam pipes carried down the pit, or, what is now more common, by boilers underground, which supply also steam for the underground hauling engines. Where the water does not accumulate very rapidly it is a very common practice to allow it to collect in a pit or sump below the working bottom of the shaft, and to draw it off in a water tub or bucket by the main engine, when tlie latter is not employed in raising coal. The laying out of a colliery, after the coal has been won, Laying out by sinkings or levels, may be accomplished in various ways, workings. according to the nature of the coal, its thickness and dip, and the extent of ground to be worked. In the South Stafford shire and other Midland coal-fields, where only shallow pits are required, and the coals are thick, a pair of pits may be sunk for a very few acres, while in the North of England, on the other hand, where sinking is expensive, an area of some thousands of acres may be commanded from the same number of pits. In the latter case, which represents the most approved practice, the sinking is usually placed about the centre of the ground, so that the workings may radiate in every direction from the pit bottom, with the view of employing the greatest number of hands to ad vantage. Where a large area cannot be commanded, it is best to sink to the lowest point of the field for the convenience of drawing the coal and water which become level-free in regard to the pit. Where properties are much divided, it is always necessary to maintain a thick barrier of unwrought coal between the boundary of the mine and the neighbouring workings, especially if the latter are to the dip. If a prominent line of fault crosses the area, it may usually be a convenient division of the field into sections or districts. The first process in laying out the workings consists in driving a gallery on the level along the course of the coal seam, which is known as a " dip head level," and a lower parallel one, in which the water collects, known as a " lodgment level." Galleries driven at right angles to these are known as " dip " or " rise headings," according to their position above or below the pit bottom. In Staffordshire the main levels are also known as "gate roads." To secure the perpendicularity of the shaft, it is necessary to leave a large mass or pillar of the seam un touched around the pit bottom. This pillar is known in Scotland as the " pit bottom stoop." The junction of the levels with the pit is known as the " pit eye ; " it is usually of an enlarged section, and lined with masonry or brick work, so as to afford room for handling the waggons or trams of coal brought from the working faces. In this portion of the pit are generally placed the furnaces for ventilation, and the boilers required for working steam- engines underground, as well as the stables and lamp cabin. Figs. 5 and G represent the pit bottom arrangements at Cambois colliery in Northumberland, which are of an ex tremely commodious character. There are four large Cornish boilers, supplying steam to the engines drawing coals from the workings, as well as to a direct-acting pump ing engine, the flame and smoke being discharged by drifts into the upcast pit. For the purpose of handling large pieces of machinery and boilers, the level at the bottom is increased to a chamber 18 feet high, and roofed with rolled iron girders of a double T section. To protect the fillers working at the bottom, strong diagonal guard timbers are placed at S in order to deflect any materials falling down the shaft, and prevent them falling into the work ings. This is an unusually large example, but is taken from a pit in the highest state of development, and making a very large daily outturn. Fia. 5. Pit eye, Gambols Colliery Vertical Section. Method of The removal of the coal after the roads have been driven working may be effected in many different ways, according to the out coal. Pillar working. FIG. 6. Pit bottom arrangements, Cambois Colliery custom of the district, These may, however, all be con sidered as modifications of two systems viz., pillar work and long-wall work, In the former, which is also known as "port and stall" or " bord and pillar" in the north of England, "pillar and stall" in South Wales, and "stoop and room " in Scotland, the field is divided into strips by numerous openings driven parallel to the main rise head ings, called " bords " or " bord gates," which are again divided by cutting through them at intervals, so as to leave a series of pillars arranged chequer-wise over the entire area. These pillars are left for the support of the roof as the workings advanc.3, so as to keep the mine open and free from waste. Fig. 1, Plate III. represents the oldest form of this class of working as practised in Scotland, from which it will be seen that if the size of the pillar is equal to tho wiilth of the stall or excavation, about f of the [MINING. whole seam will be removed, the remainder being left in the pillars. A portion of this may be got by the process known as robbing the pillars, but the coal so obtained is liable to be very much crushed from the pressure of the superincumbent strata. This crushing may take place either from above or below, producing what are known as " creeps " or " sits." A coal seam with a soft pavement and a hard roof is the most subject to a " creep." The first indication is a dull hollow sound heard when treading on the pavement or floor, probably occasioned by some of the individual layers parting from each other as shown at a fig. 7 ; FIG. 7. " Creeps" in Coal-Mines. the succeeding stages of creep are shown at b, c, d, f, and g, in the same figure ; the last being the final stage, when the coal begins to sustain the pressure from the overlying strata, in common with the disturbed pavement. " Sits " are the reverse of creeps ; in the one case the pavement is forced up, and in the other the roof is forced or falls down, for want of proper support or tenacity in itself. This accident generally arises from an improper size of pillars ; some roofs, however, are so difficult to support that sits take place where the half of the coal is left in pillars. Fig. 8 will convey a general idea of the appearance of sits, k, m, n showing different stages. FIG. 8. " Sits " in Mines. The modern method of pillar working is shown in Plate IV. In the Northumberland steam-coal district, where it is carried out in the most perfect manner, the boards are 5 to 6 yards in width, while the pillars are 22 yards broad and 30 yards long, which are subsequently got out on coming back. In the same figure is also shown the method of working whole coal and pillars at the same time, a barrier of two or three ranges of pillars or a rib of solid coal being left between the working in the solid and those in the pillars. The space from which the entire quantity of coal has been removed is known in different districts as the "goaf," "gob," or " waste." Fig. 9 represents the Lancashire system of pillar- working. The area is laid out by two pairs of level drifts, parallel to each other, about 150 yards apart, which are carried to the boundary. About 100 yards back from the boundary a communication is made between these levels, from which other levels are driven forward, dividing the coal into ribs of about 25 or 30 yards wide, which are then cut back by taking off the coal in slices from the level tov ards the rise in breadths of about six yards. By this method the whole of the coal is got backwards, the main roads being kept in solid coal ; the intermediate levels not

being driven till they are wanted, a greater amount cf sup

MODES OF WORKING.]

COAL 65 port is given, and the pillars are less crushed than is usual in pillar working. ,: 8 U N D A R Y Fio. 9. Lancashire method of working Coal In the South Wales system of working, cross headings are driven from the main roads obliquely across the rise to get a sufficiently easy gradient for horse roads, and from these the stalls are opened out with a narrow entrance, in order to leave support on either side of the road, but aftsr- wards widening to as great a breadth as the seam will allow, leaving pillars of a minimum thickness. The cha racter of such workings is very irregular in plan, and as the ventilation is attended with considerable difficulty, it is now becoming generally superseded by more improved methods. The second great principle of working is that known as long-wall or long-work, in which the coal is taken away either in broad faces from roads about 40 or 50 yards apart and parallel to each other, or along curved faces between roads radiating from the pit bottom the essential feature in both cases being the removal of the whole of the coal at once, without first sub-dividing it into pillars, to be taken away at a second working. The roof is tem porarily supported by wooden props or pack walling of stone, for a sufficient breadth along the face to protect the work men, and allow them to work together behind. The general character of a long- wall working is shown iu fig. 10, which Fid. 10. Long-will method of working Coal in Derbyshire. represents an area of about 500 acres of the bottom hard steam coal at Shipley in Derbyshire. The principal road extends from the shafts southward ; and on both sides of it the coal has been removed from the light-shaded area by cutting it back perpendicularly towards the boundaries, along faces about 50 yards in length, those nearest to the shaft being kept in advance of those farther away, pro ducing a step-shaped outline to the face of the whole coal. It will be seen that by this method the whole of the seam, with the exception of the pillars left to protect the main roadways, is removed. The roads for drawing the coal from the working faces to the shaft are kept open by walling through the waste or goaf produced by the fall of the un supported roof. The straight roads are the air-ways for carrying pure air from the down-cast shaft to the working faces, while the return air passes along the faces and back to the up-cast by the curved road. The above is the method of working long-wall forward, i.e., taking the coal iu advance from the pit towards the boundary, with roads kept open through the gob. Another method consists in driving towards the boundary, and taking the coal back ward towards the shafts, or working homeward, allowing the waste to close up without roads having to be kept open through it. This is of course preferable, but is only applicable where the owner of the mine can afford to expend the capital required to reach the limit of the field in excess of that necessary when the raising of coal pro ceeds pari passu with the extension of the main roads. Fig. 9 is substantially a modification of this kind of long- wall work. Plate III. fig 2, represents a method of working prac tised in the South Yorkshire district, known as bords and South banks. The field is divided by levels and headings into Yorks rectangular banks, while from the main levels bords or method - wickets about 30* yards wide, separated from each other by banks of about the same width, are carried forward in long- wall work, as shown on the left side of the figure, the waste being carefully packed behind so as to secure the ventila tion. When these have been worked up to the extremity, as shown on the right side, the intermediate bank is removed by working backward towards the level. This system, therefore, combines both methods of long-wall working, but is not generally applicable, owing to the diffi culty of ventilation, due to the great length of air-way that has to be kept open around the waste on each bank. The relative advantages of the different methods may be generally stated as follows. Long-wall work is best suited for thin coals, and those having a good roof, i.e., one that gives way gradually and fills up the excavation made by removing the coal without scaling off suddenly and falling into the working faces, when practically the whole of the coal may be removed. Against these advantages must be placed the difficulties attending the maintenance of roads through the goaves, and in some cases the large proportion of slack to round or large coal obtained. Pillar working, in the whole coal, is generally reputed to give a more advan tageous proportion of round coal to slack, the latter being more abundantly produced on the removal of the pillars, but as these form only a small portion of the whole seam, the general yield is more advantageous than in the former method. The ventilation of pillar working is often attended with difficulty, and the coal "is longer exposed to the influ ence of the air, a point of importance in some coals, which deteriorate in quality when exposed to a hot damp atmo sphere. The great increase in the size of the pillars in the best modern collieries worked upon this principle has, however, done much to approximate the two systems to an equality in other respects. The working of very thick seams presents certain special Working peculiarities, owing to the difficulties of supporting the roof tnick in the excavated portions, and supplying fresh air to the sc workings. The most typical example of this kind of work ing in England is afforded by the thick coal of South Staffordshire, which consists of a series of closely associated coal seams, varying from 8 to 12 or 13, divided from each other by their partings, but making together one great bed of from 25 to 40 feet or more in thickness. The partings together do not amount to more than 2 or 3 feet. The method of working which has been long in use is repre sented in fig. 11. The main level or gate road is driven in the benches coal, or lower part of the seam, while a smaller drift for ventilation, called an air heading, is VI - 9 f)f> (J A L [MINING. carried above it in one of the upper beds called the slipper coal From the gate road a heading called a bolt-hole is opened, and extended into a large rectangular chamber, known as a " side of work," large pillars being left at regular Fro. 11. South Staffordshire method of working Thick Coal. intervals, besides smaller ones or cogs. The order in which the coal is cut is shown in the dotted and numbered squares in the figure. The coal is first cut to the top of the slipper coal from below, after which the upper portion is either broken down by wedging or falls of itself. The working of these upper portions is exceedingly dangerous, owing to the great height of ths excavations, and fatal accidents from falls of roof are in consequence more common in South Staffordshire than in any other coal-field in this country. The air from the down-cast shaft enters from the gate road, and passes to the up-cast through the air heading above. About one-half of the total coal (or less) is obtained in the first working ; the roof is then allowed to fall, and when the gob is sufficiently consolidated, fresh roads are driven through it to obtain the ribs and pillars left behind by a second or even, in some cases,. a third working. The loss of coal by this method is very considerable, besides great risk to life and danger from fire. It has, therefore, been to some extent superseded by the long-wall method, the upper half being taken at the first working, and removed as completely as possible, working backwards from the bound aries to the shaft. The lower half is then taken in the same manner, after the fallen roof has become sufficiently consolidated to allow the mine to be re-opened. In the working of thick seams inclined at a high angle, such as those in the south of France, and in the lignite mines of Styria and Bohemia, the method of working in horizontal slices, about 12 or 15 feet thick, and filling up the excavation with broken rock and earth from the sur face, is now generally adopted in preference to the systems formerly used. At Monceaux les Mines, in France, a seam 40 fe<:t thick, and dipping at an angle of 20 degrees, is worked in the following manner. A level is driven in a sandstone forming the floor, along the course of the coal, into which communications are made by cross cuts at intervals of 16 yards, which are driven across to the roof, dividing up the area to be worked into panels- These are worked backwards, the coal being taken to a height of 20 feet, the opening being packed up with stone sent down from the surface. As each stage is worked out, the floor level is connected with that next below it by means of an incline, which facilitates the introduction of the packing material. Stuff containing a considerable amount of clay is found to be the best suited for the purpose of filling, at it consolidates readily under pressure The actual cutting of the coal is chiefly performed by Method manual labour, the tool employed being a sharp-pointed of cutti double-armed pick, which is nearly straight, except when required for use in hard rock, when the arms are made with an inclination or " anchored." The terms pike, pick, mandril, and slitter are applied to the collier s pick in different districts, the men being known as pikemen or hewers. In driving levels it is necessary to cut grooves vertically parallel to the walls, a process known as shearing; but the most important operation is that known as holing or kirving, which consists in cutting a notch or groove in the floor of the seam to a depth of about 3 feet, measured back from the face, so as to leave the overhanging part unsupported, which then either falls of its own accord within a few hours, or is brought down either by driving wedges along the top, or by blasting with gunpowder. The process of holing in coal is one of the severest kinds of human labour. It has to be performed in a constrained posi tion, and the miner lying on his side has to cut to a much greater height, in order to get room to carry the groove in to a sufficient depth, than is required to bring the coal down, giving rise to a great waste in slack as compared with machine work. This is sometimes obviated by holing in the beds below the coal, or in any portion of a seam of inferior quality that may not be worth working. This loss is proportionately greater in thin than in thick seams, the same quantity being cut to waste in either case. The method of cutting coal on the long- wall system is seen in fig. 1 2, repre- Fio. 12. Long- wall working-face Plan and Section. senting the working at the Shipley colliery. The coal is 40 inches thick, with a seam of fire-clay and a roof of black shale , about 6 inches of the upper part, known as the roof coal, not being worth working, is left behind. A groove of triangular section of 30 inches base and 9 inches high is cut along the face, inclined timber props being placed at inter vals to support the overhanging portion until the required length is cut. These are then removed, and the coal is allowed to fall, wedges or blasting being employed when necessary. The roof of the excavation is supported as the coal is removed, by packing up the waste material, and by

a double row of props, two feet from each other, placed tem CUTTING MACHINES.]

COAL 67 porarily along the face. These are placed 5 feet apart, the props of the back row alternating with those in front. The props used are preferably of small oak or English larch, but large quantities of fir props, cut to the right length, aro also imported from the north of Europe. As the work proceeds onwards, the props are withdrawn and replaced in advance, except those that may be crushed by the pressure or buried by sudden falls of the roof. In Yorkshire hollow square pillars, formed by piling up short blocks of wood or chocks, are often used instead of props formed of a single stem. Iron pit props have been proposed at different times, but their use has not become general. When the coal has been under-cut for a sufficient length, the struts are withdrawn, and the overhanging mass is allowed to fall during the time that the workmen are out of the pit, or it may be brought down by driving wedges, or if it be of a compact character a blast of gunpowder in a bore hole near tho roof may be required. Sometimes, but rarely, it happens that it is necessary to cut vertical grooves in the face to determina the limit of the fall, such limits being usually dependent upon the cleet or divisional planes in the coal, especially when the work is carried perpen dicular to them or on the end. The substitution of machinery for hand labour in cut- Coal- ting coal has long been a favourite problem with iuven- c tors, the earliest plan being that of Menzies, in 1761, who proposed to work a heavy pick underground by power transmitted from an engine at the surface, through the agencies of spear-rods and chains passing over pulleys; but none of the methods suggested proved to be prac tically successful until the general introduction of com pressed air into mines furnished a convenient motive power, susceptible of being carried to considerable distances without any great loss of pressure. This agent has of late years been applied in various ways, in machines which either imitate the action of the collier by cutting with a pick or make a groove by rotating cutters attached to an endless chain or a revolving disc or wheel. The most successful of the first class, or pick machines, is that of Mr William Firth of Sheffield, represented in fig. 13. It consists esseu- FIG. 13. Firth s Coal-cutting Machine. tially of a horizontal piston and cylinder engine fixed upon a platform carried upon four wheels, which are coupled to gether by side rods, so that on motion being communi cated by means of a mitre wheel in the hind axle, it can be moved forward by hand. On the forward end of the frame are two bosses forming the centres for a pair of bell cranks or bent levers placed close to the ground, and facing in opposite directions, either one of which can be con nected with the piston rod. The outer arm of each lever carries a square socket, into which is fixed the pick, which has two cutting heads, one placed a little in front of the other so as to cut to the whole depth at one operation. In the older forms picks of different length were used, and it was necessary to go over the work a second or third time, in order to hole to the full depth. The cutting- points are loose, being secured by cotters to the pick head, so that broken or blunted ones can be readily replaced without removing the pick arm. The power used is air, at about 40 to 60 ft> above atmospheric pressure. It is con ducted from the reservoir connected with a compressing engine at the surface, through iron pipes fixed in the pit, and along the main roads to the working face, where thick vulcanized india-rubber pipes are used, sufficient length of pipe lying loose on the ground to allow the engine to move freely, the connection being made by a screwed joint at the back of the slide-valve chest. The valve is worked by tappets on the piston-rod, so as to be perfectly self- acting when properly adjusted ; it can also be moved by hand. The pick holders face in opposite directions, in order that the machine may be worked from either side. The size of the machine as ordinarily made is about 4 feet in length, 2 feet 2 inches high, and from 18 to 24 inches gauge of rails. The weight is about 15 cwt. The working speed is from 60 to 90 strokes per minute, corresponding to a length of from 10 to 20 yards, cut to a depth of 3 feet per hour. At the former rate, or 60 yards per shift of 6 hours, the work done corresponds to that of twelve average men. The width of the groove is from 2 to 3 inches at the face, diminishing to 1^ inches at the back, the proportion of waste being very considerably diminished as compared with the system of holing by hand. The use of this machine has allowed a thin seam of cannel, from 10 to 14 inches in thickness, to be worked to profit, which had formerly been abandoned as too hard to be worked by hand-labour. An earlier form of the second class of machine, in which the cutters have a continuous motion like those of a slotting machine, is that invented by Mr William Peace in the Wigan district, which is reproduced from the last edition as illustrating the principle which has since been carried out by other inventors in a more convenient and simplified form. It is represented in Plate V., figs, 1, 2, and 3. AAA is the frame, upon which are fixed one or more cylinders B, arranged so as to turn a crank shaft C, fixed to the frame, as is also another shaft D. This latter is capable of being turned by the former, by means of mitre or bevel wheels EEE ; upon the lower end of the latter shaft D is placed a wheel termed the driving wheel, having upon its periphery a groove with 08 C A L [MINING. suitable projections for working into and propelling a chain or band. Beneath or to the side of the frame (or both) is fixed temporarily or otherwise a lever, the extremity of which is constructed to carry a wheel called the ter minal wheel, marked II H ; a chain or band is made to pass round the driving and terminal wheels, and by means of the driving wheel FF it is made to revolve. Into the chain are fixed cutters of different forms (see the parts marked, figs. 4, 5, 6, and 7), which, when the machine is in action, revolve with it, and upon being pressed or drawn against the coal, erode and excavate the same. The dis tance of the excavation from the face of the coal is governed by the dimensions of the machine, and by the length of the lever and the distance between the driving and terminal wheels. The arrangements of the lever allow it to revolve, and to excavate any given range ; see dotted lines fig. 1. If found necessary, two or even three levers may be in operation at the same time, and arranged to cut in any direction. Other parts of the machine not particularly de scribed are capable of elevating and depressing the front part of the machine, marked V, T, U, W ; and those marked X, Y, Z, and K are capable of propelling the machine whilst at work, by acting against the prop. The Gartsherrie machine of Messrs Baird is of the same character, but the chain of cutters works round a fixed frame or jib projecting at right angles from the engine car riage, instead of traversing upon a centre, an arrangement which makes it necessary to cut from the end of the block of coal to the full depth, instead of holing into it from the face. The forward feed is given by a chain winding upon a drum, which hauls upon a pulley fixed to a prop about 30 yards in advance. This is one of the most compact form of machines, the smaller size being only 20 inches high. With an air pressure of from 35 to 40 ft> per square inch, a. length of from 300 to 350 feet of coal is holed, 2 ft, 9 in. deep, in the shift of from 8 to 10 hours. One of the simplest forms of coal-cutting machines is that of Messrs Winstanly & Barker (fig. 14), which is driven Fro. 14. Winstanly & Barker s Coal-cutting Machine Plan. by a pair of oscillating engines placed on a frame run ning on rails in the usual way. The crank shaft carries a pinion which gears into a toothed wheel of a coarse pitch, carrying cutters at the ends of the teeth. This wheel is mounted on a carrier which, being movable about its centre by a screw gearing worked by hand, gives a radial sweep to the cutting edges, as in the machine figured in Plate V. When at work it is slowly turned until the carrier is at right angles to the frame, when the cut has attained the full depth. The forward motion is given by a chain-winding upon a crab placed in front, which is worked by a boy who hauls it slowly forward. With 25 R) pressure it will hole 3 feet deep, at the rate of 30 yards per hour, the cut being only 2| in. high, but it will only work on one side of the carriage. Another kind of application of machinery to coal mining is that of Messrs Bidder & Jones, which is intended to replace the use of blasting with gunpowder for bringing down the coal, a practice which in fiery collieries is often attended with considerable danger from the flash of the ex plosion firing the gas given off the coal. It consists of a small hydraulic press, which forces a set of expanding bits or wedges into a bore-hole previously bored by a long screw augur or drill, worked by hand, the action of the press being continued until a sufficient strain is obtained to bring down the coal. The arrangement is, in fact, a modification of the plug and feather system used in stone quarrying for obtaining large blocks, but with the substitution of the powerful rending force of the hydraulic press for hand -power in driving up the wedges. This apparatus has been used at Harecastle in North Staffordshire, and found to work well, but with the disadvantage of bringing down the coal in unmanageably large masses. The use of gunpowder in very fiery mines is always attended with danger, and a method of wedging down coal sufficiently perfected to be of general application would add greatly to the security of the colliers in work ing such mines. The removal of the coal when broker from the work- ing faces to the pit bottom or to the main levels is effected mainly by hand labour when the mine is small, and the distances to be traversed inconsiderable, and in mines of greater extent by horse or steam traction. The simplest method is that of loading the broken coal on to a sledge, which is dragged along the floor to the level, but now the practice of carrying railways to the face is almost universal. The old form of flat rail or tram is still largely used, the waggons having sharp- edged disc wheels, but probably edge rails and flanged wheels are now more general. The class of rail used is generally a flat-bottomed or bridge section, weighing from 15 to 25 ft> per yard, laid upon cross sleepers, which, in roads that are intended to be kept open for some time, are fixed down firmly, but are laid in a temporary manner along the working faces, and in similar positions where it is necessary to be continually shifting them, as, for instance, wheie coal-cut ting machines are used. The arrangement of the drawing roads at the face of a long-wall colliery is seen in the plan fig. 12, where the rails are brought to the face upon a smooth iron plate, upon which the trams can be easily handled by turning on the flanges of the wheels. The names applied to the vehicles in which the coal is carried vary considerably, as do also their size and capacity. The word " corf " or " corve," representing the old basket sledge, is one of the most generally used, as are " tram," signifying a tram waggon, and " tub," of the same signification as the last, but a representative of the old method of drawing in wooden buckets. In South Staffordshire and other Midland districts, a contrivance called a "skip" is the representative method of conveyance ; this consists of a platform with tram wheels, upon which the coal is built up to a consider able height, the large pieces round the sides being kept to gether by loose rings of sheet iron, and the intermediate spaces packed full with small coal, the whole arrange ment representing a kind of cask. This, however, like most of the similar primitive methods, is giving way to the more improved system of tubs or trams. These are small railway trucks, generally with flanged wheels and square- sided bodies, either of wood or wrought iron, varying in capacity from 4 cwt. in thin seams to 10 or 12 cwt. in thicker seams. In the removal of the coal from the workings the first portion of the journey .is generally performed by hand- Coal wedging Under- g r undc ve y ance CONVEYANCE.] COAL power, boys being employed to push the trams before them to the main roads. In the thin seams jf South York shire and other places, considerable journeys are often performed in this way, the boys known, as " hurriers" or " putters" being obliged to crawl at full length, owing to the lowness of the excavation. As a general rule boys are not allowed to work in collieries when below 12 years of age, but in these thin mines special exemptions are granted, permitting the use of younger boys as putters when re quired. Where the levels are large, horse traction is in common use; the trams are formed up into trains, and from 6 to 15 vehicles are drawn by one horse. A considerable number of ponies are imported into the northern ports of this country from Norway and Iceland for this purpose every year. The supply of horses is, however, becoming scarcer, and the price higher, so that the use of under ground engines is generally adopted where the output is sufficiently large to justify the expenditure. This is done by hauling or, as it is called in the North of England, lead ing the trains of tubs by rope traction. In a large colliery where the shafts are situated near the centre of the field, and the workings extend on all sides, both to the dip and rise, the drawing roads for the coal may be of three differ ent kinds, (1) levels driven at right angles to the dip, suitable for horse roads, (2) rise ways, known as jinny roads, jig-brows, or up-brows, which, when of sufficient slope, may be used as self-acting planes, i.e., the loaded waggons may be made to pull back the empty ones to the working faces, and (3) dip or down-brows, requiring engine power. A road may be used as a self-acting or gravitating incline when the gradient is 1 in 30 or steeper, in which case the train is lowered by a rope passing over a pulley or brake drum at the upper end, the return empty train being attached to the opposite end of the rope and hauled up by the descend ing load. The arrangements for this purpose vary, of course, with the amount of work to be done with one fixing of the machinery ; where it is likely to be used for a considerable time, the drum and brake are solidly constructed, and the ropes of steel or iron wire carefully guided over fric tion rollers, placed at intervals between the rails to pre vent them from chafing and wearing out on the ground. Where the load has to be hauled up a rising gradient, underground engines, driven by steam or compressed air, are now generally used. In some cases steam generated in boilers at the surface is carried in pipes to the engines below, but this can be done with less loss of power by send ing down compressed air in the same way. The use of underground boilers placed near the upcast pit, as in fig. 6, so that the smoke and gases help the ventilat ing furnace, is most convenient in the majority of cases. Water-pressure engines, driven by a column of water equal to the depth of the pit, have also been employed for hauling. These can, however, only be used advantageously where there are fixed pumps, the fall of water generating the power resulting in a load to be removed by the expen diture of an equivalent amount of power in the pumping engine above that necessary for keeping down the mine water. There are four principal methods in which steam power can be applied to underground traction. These, which have been discussed in the fullest manner in the Report of the North of England Institute of Mining Engineers for 1867- 68, are as follows : 1. Tail rope system. 2. Endless chain system. 3. Endless rope system on the ground. 4. Endless rope system overhead. The three last may be considered as modifications of the same principle. In the first, which is that generally used in Northumberland and Durham, a single line of rails is used, the loaded tubs being drawn "out bye," i.e., towards the shaft, and the empty ones returned " in bye," or towards the working faces, by reversing the engine ; while in the other systems, double lines, with the rope travelling continu ously in the same direction, are the rule. On the tail rope plan the engine has two drums worked by spur gearing-, which can be connected with, or cast loose from, the driving shaft at pleasure. The main rope, which draws out the loaded tubs, coils upon one drum, and passes near the floor over guide sheaves placed about 20 feet apart. The tail rope, which is of lighter section than the main one, is coiled on the second drum, passes over similar guide sheaves placed near the roof or side of the gallery round a pulley at the bottom of the plane, and is fixed to the end of the train or set of tubs. When the load is being drawn out, the engine pulls directly on the main rope, coiling it on to its own drum, while the tail drum runs loose pay ing out its rope, a slight brake pressure being used to pre vent its running out too fast. When the set arrives out bye, the main rope will be wound up, and the tail rope pass out from the drum to the end and back, i.e., twice the length of the way; the. set is returned in bye, by reversing the engine, casting loose the main, and coupling up the tail drum, so that the tail rope is wound up, and the main rope paid out. This method, which is the oldest, having been in use for twenty-five years or more in the North of Eng land, is best adapted for ways that are nearly level, or when many branches are intended to be worked from one engine, and can be carried round curves of small radius without deranging the trains; but as it is intermittent in action, considerable engine-power is required in order to get up the required speed, which is from 8 to 10 miles per hour. From 8 to 10 tubs are usually drawn in a set, the ways being often from 2000 to 3000 yards long. In dip workings the tail rope is often made to work a pump con nected with the bottom pulley, which forces the water back to the cistern of the main pumping engine in the pit. For the endless chain system, which is much iised in the Wigan district a double line of way is necessary, one line for full and the other for empty tubs. The chain passes over a pulley driven by the engine, placed at such a height as to allow it to rest upon the tops of the tubs, and round a similar pulley at the far end of the plane. The forward edge of the tub carries a projecting pin or horn, with a notch into which the chain falls which drags the tub forward. The road at the outer end is made of a less slope than the chain, so that on arrival the tub is lowered, clears the pin, and so becomes detached from the chain. The tubs are placed on at intervals of about 20 yards, the chain moving continuously at a speed of from 2^ to 4 miles per hour. This system presents the greatest advantages in point of economy of driving power, especially where the gradients are variable, but is expensive in first cost, and is not well suited for curves, and branch roads cannot be worked con tinuously, as a fresh set of pulleys worked by bevel gear ing is required for each branch. The endless rope system may be used with either a single or double line of way, but the latter is more gene rally advantageous. The rope, which is guided upon sheaves between the rails, is taken twice round the head pulley; or a Fowler s clip pulley may be used. It is also customary to use a stretching pulley to keep the rope strained when the pull of the load diminishes. This is done by passing a loop at the upper end round a pulley mounted in a travelling frame, to which is attached a weight of about 15 cwt. hanging by a chain. This weight pulls directly against the rope ; so if the latter slacks, the weight pulls out the pulley frame and tightens it up again. The tubs are usually formed into sets of from 2 to 12, the front one being coupled up by a short length of chain 70 COAL [MINING. to a clamping hook formed of two jaws moulded to the curve of the rope which are attached by the " run rider," as the driver accompanying the train is called. This system in many respects resembles the tail rope, but has the advantage of working with one-third less length of rope for the same length of way. The endless rope system overhead is substantially similar to the endless chain. The waggons are attached at intervals by short lengths of chain lapped twice round the rope and hooked into one of the links, or in some cases the chains are hooked into hempen loops on the main rope. One of the most important branches of colliery work is the management of the ventilation, involving as it does the supply of fresh air to the men working in the pit, as well as the removal of inflammable gases that may be given off by the coal. This is effected by carrying through the workings a large volume of air Avhich is kept continu ally moving in the same direction, descending from the surface by one or more pits known as intake or downcast pits, and leaving the mine by a return or upcast pit. Such a circulation of air can only be effected by mechanical means when the workings are of any extent, as will be apparent from the following considerations : If the shafts A and B, fig. 15, were of equal depth from the horizon tal plane, and connected by the mine C, the air would fill the openings and remain quiescent. If the one were to the dip of the other, but communicating with the surface at a higher level, as by fig. 16, it would sometimes happen, in summer, that D would be the down cast, and E the upcast, and in winter, E the downcast, and D the upcast. These conditions are induced by the tern- Fig. 16. perature of the earth at a certain depth being nearly con stant, while the atmosphere is changeable, the column of air in D d being at a lower temperature in summer than the column of air E e, and the reverse in winter. The methods actually adopted are (1 ) The rarefaction of the air in the upcast pit by a furnace placed at the bottom; and (2) Exhaustion by machinery at the surface. The former plan, although hitherto most generally used, is in many places becoming replaced by some form of machine. Furnace. The usual form of ventilating furnace is a plain fire grate placed under an arch, and communicating with the upcast shaft by an inclined drift. It is separated from the coal by a narrow passage walled and arched in brick work on both sides. The size of the grate varies with the requirements of the ventilation, but from G to 10 feet broad and from G to 8 feet long are usual dimensions. At Shircoaks Colliery, in Nottinghamshire, a furnace con suming G tons of slack per 24 hours upon a grate surface of 72 square feet maintains a circulation of about 120,000 cubic feet per minute. At Iletton Colliery, Durham, the grate is a long, narrow rectangle, 25 feet by 5 feet, with numerous furnace-doors on the long side, so arranged that the surface fired may be varied according to the amount of draught required. There are two bunker- holes for coals, and a stoking passage, 7 feet wide, in front of the furnace. The fire should be kept as thin and bright as possible, to reduce the amount of smoke in the upcast. When the mine is free from gas, the furnace may be worked by the return air, but it is better to take fresh air directly from the downcast by a scale, or split, from the main current. The return air from fiery workings is never allowed to approach the furnace, but is carried into the upcast by a special channel, called a dumb drift, some distance above the furnace drift, so as not to come in con tact with the products of combustion until they have been cooled below the igniting point of fire-damp. Where the upcast pit is used for drawing coal, it is usual to discharge the smoke and gases through a short lateral drift near the surface into a tall chimney, so as to keep the pit-top as clear as possible for working. Otherwise the chimney is built directly over the mouth of the pit. Various kinds of machines for ventilation, both by direct M exhaustion and centrifugal displacement, have been tried ven both in England and in Belgium. Of the former class are the great bell machines, resembling gasometers, 12 feet to 22 feet in diameter, and 9 feet high, moving in a water tank with balanced flap valves for alternately admitting and exhausting the air. These were used at Marihaye, near Li6ge, and at Cwm Avon in South Wales, by Mr Struve". Perhaps the largest of the class of piston machines is that at Nixon s Navigation Pit, near Aberdare, which has rectangular pistons, 30 feet by 22 feet, moving hori zontally through a stroke of 7 feet, the lower edge being supported by rollers running on rails. The great weight of the moving parts in this class of machine makes them incapable of acting at any very high speed, and conse quently expensive for the amount of work done. This is in some degree obviated in the rotary piston machines of Fabry and Lemielle, the former resembling in principle Hoot s blower, now so much used in blowing foundry and smiths fires, but on a larger scale. Lemielle s ventilator is a vertical drum revolving eccentrically within a cylin drical casing. The drum carries three jointed blades, which are drawn in or out by radius bars as it revolves, so as to enclose and sweep out at each revolution tbe body of air included between the two cylinders. This is one of the best machines of its class, producing a comparatively high effect for the power expended. An American machine of this kind is described and figured in the article BELLOWS, vol. iii. p. 552, fig. 5. Of late years, various kinds of centrifugal machines, or fans, have come into use instead of ventilating furnaces. One of the most successful of these is that invented by Mr Guibal of Lie ge, represented in fig. 17. The fan has eight arms, framed together of wrought-iron bars, with diagonal struts, so as to obtain rigidity with comparative lightness, carrying flat close-boarded blades at their extremities. It revolves with the smallest possible clearance in a chamber of masonry, one of the side walls being perforated by a large round hole, through which the air from the mine is admitted to the centre of the fan. The lower quadrant of the casing is enlarged spirally, BO as to leave a narrow rectangular opening at the bottom, through which the air is discharged into a chimney of gradually increasing section carried to a height of about 25 feet. The size of the discharge aperture can be varied by means of a flexible wooden shutter sliding VENTILATION.] COAL 71 in a groove in a cast-iron plate, curved to the slope of the casing. By the use of the spiral guide casing and the FIG. 17. Guibal s Fan. chimney, the velocity of the effluent air is gradually reduced up to the point of final discharge into the atmosphere, whereby a greater useful effect is realized than is the case when the air streams freely from the circumference with a velocity equal to that of the rotating fan. The power is applied by steam acting directly on a crank at one end of the axle. In most of the newer examples, which are generally of large size, the power is divided, an engine being placed on each side. At Washington Colliery, Durham, a machine of 36 feet diameter, 12 feet breadth of face, and 13 feet diameter of intake passage, draws 120,000 cubic feet of air per minute, when making 38 revolutions Another at Usworth, 48 feet diameter and 12 feet breadth of face, driven by two high-pressure engines, with cylinders 3 feet in diameter and 3 feet stroke, equal to about 280 horse-power, exhausts 200,000 cubic feet per minute. The useful effect realized under the most favourable conditions is as much as 50 per cent, of that of the steam power employed. Waddle s fan, represented in fig. 18, is an example of FIG. 18. -Waddle s Fan. another class of centrifugal ventilator, in which a close cas ing is not used, the air exhausted being discharged from the circumference directly into the atmosphere. It con sists of a hollow sheet-iron drum formed by two conoidal tubes, united together by numerous guide blades, dividing it up into a series of rectangular tubes of diminishing sec tion, attached to a horizontal axle by cast-iron bosses and wrought-iron arms. The tubes at their smallest part are connected to a cast-iron ring, 10 feet in diameter, but at their outer circumference they are only 2 feet apart. The extreme diameter is 25 feet. A fan of these dimen sions atBrownhills in Staffordshire, in making 50 revolutions per minute, circulates 47,000 cubic feet of air through the workings. It has also been in use for some years in South Wales, and is found to work well; it is less expensive in first cost than Guibal s, although proportionally less economical from the smaller effect realized for the power expended. Another method of colliery ventilation is that by jets of steam blowing off at a high velocity into the upcast shaft, and producing a draught similar to that of the exhaust blast in the chimney of a locomotive. This plan found several advocates some years since, and was the subject of numerous comparative trials against the ventilating fur nace in the North of England, but the results were unfa vourable, the amount of air circulation produced being exceedingly small for the fuel expended. It seems probable^ however, that this want of success was in great part due to the defective character of the apparatus applied, and that, with properly-constructed aspirators and discharge passages, the steam jet may prove to be a very efficient means of ventilation. The comparative merits of furnace and machine ventila tion have long been discussed without any definite result. The former was at one time regarded in England as practi cally superior in every respect, but this opinion has been modified since the introduction of the improved forms of fans which have been worked to a considerable extent. In France and Belgium, on the contrary, machine ventilation has been more generally in favour. For a deep and ex tensive mine where the coal is not fiery, the furnace is undoubtedly the simplest and most efficacious method of producing a large circulation of air ; but for moderate depths, especially with fiery return air, a ventilating machine at the surface is in many cases to be preferred. There ia also an important advantage procured by the latter, namely, that of reserve power, so that a larger circulation may be obtained immediately in case of need, e.g., when the barometer falls suddenly, by merely increasing the speed of rotation, which cannot so readily be done with the furnace, which has a tendency to slacken at the time when the increased work is wanted. The quantity of air required for a large colliery depends Distribu- upon the number of men employed, as for actual respira- tion of air tion from 100 to 200 cubic feet per minute should be allowed. In fiery mines, however, a very much larger amount must be provided in order to dilute the gas to the point of safety. Even with the best arrangements a dan gerous increase in the amount of gas is not un frequent from the sudden release of stored up masses in the coal, which, overpowering the ventilation, produce magazines of explosive material ready for ignition when brought in con tact with the flame of a lamp or the blast of a shot. The management of such places, therefore, requires the most constant vigilance on the part of the workmen, especially in the examination of the working places that have been standing empty during the night, in which gas may have accumulated, to see that they are properly cleared before the new shift commences. The actual conveyance or coursing of the air from the intake to the working faces is effected by splitting or dividing the current at different points in its course, so as to carry it as directly as possible to the places where it is required. In laying out the mine, it is customary to drive the levels or roads in pairs, communication being made between them at intervals by cutting through the inter mediate pillar, the air then passes along one, and returns by the other. As the roads advance other pillars are driven through in the same manner, the passages first made being closed by stoppings of broken rock, or built up with brick and mortar walls, or both. When it is desired to preserve a way from one road or similar class of work ing to another, double doors placed at sufficient intervals apart to take in one or more trams between them whon closed are used, forming a kind of lock or sluice. These are made to shut air-tight against their frames, so as to 72 C A L [MINING. prevent the air from taking a short cut back to the up cast, while preserving free access between the different districts without following the whole round of the air ways. The ventilation of ends is effected by means of brattices or temporary partitions of thin boards placed midway in the drift, and extending to within a few feet of the face. The air passes along one side of the brattice, courses round the free end, and returns on the other side. In many cases a light but air-proof cloth, specially made for the purpose, is used instead of wood for brattices, as being more handy and more easily removed. In large mines where the air- ways are numerous and complicated, it often happens that currents travelling in opposite directions are brought together at one point. In these cases it is neces- Crossings. sary to cross them in the manner shown in fig. 2, Plate III. The return air is usually made to pass over the intake by a curved drift carried some distance above in the solid measures, both ways being arched in brickwork, or even in some cases lined with sheet-iron so as to ensure a separation not likely to be destroyed in case of an ex plosion. The relation of the ventilation to the workings under the different systems is indicated on the several plates by arrows and other signs, from which the general character of the arrangements adopted can be made out without further description. Lighting. The lighting of underground workings in collieries is closely connected with the subject of ventilation. In many of the smaller pits in the Midland districts, and generally in South Staffordshire, the coals are sufficiently free from gas, or rather the gases are not liable to become explosive when mixed with air, to allow the use of naked lights, candles being generally used. Oil lamps are em ployed in many of the Scotch collieries, and are almost universally used in Belgium and other Continental coun tries. The buildings near the pit bottom, such as the stables and lamp cabin, and even the main roads for some distance, are often in large collieries lighted with gas brought from the surface, or in some cases the gas given off by the coal is used for the same purpose. Where the gases are fiery, the use of protected lights or safety lamps becomes a necessity. Composi- The nature of the gases evolved by coal when freshly tion of gas exposed to the atmosphere has been investigated by several y chemists, more particularly by Playfair and Meyer. The latter observer found the gases given off by coal from the district of Newcastle and Durham to contain carbonic acid (anhydride), marsh gas or light carburet ted hydrogen (the fire-damp of the miner), oxygen, and nitrogen. A newer investigation, by Mr J. W. Thomas, of the gases dissolved or occluded in coals from South Wales basin shows them to vary considerably with the class of coal. The results given below, which are selected from a much larger series published in the Journal of the Chemical Society, were obtained by heating samples of the different coals in vacuo for several hours at the temperature of boiling water.

Composition in Volumes per cent.

olunie L 

Quality. Colliery. per ton in cubic feet. Car bonic Acid Oxvgen. Marsh Gas. Nitro gen. Bituminous. Cwm Clydach. 1972 5-41 1-05 6"- 76 2970

Lnntwlt. 14-34 9-4:i 2-25 31-95 5G 34 Steam. Navigation. 89-62 13-21 0-49 81-64 4-C6 Anthracite. -J I 19894 2-C2 ... 93-13 4-25 In one instance, about 1 per cent, of bydride of ethyl was found in the gas from a blower in a pit in the Rhondda dis trict, which was collected in a tube and brought to the surface to be used in lighting the engine-room and pit-bank. The gases from the bituminous house coals of South Wales are comparatively free from marsh gas, as compared with thosa from the steam coal and anthracite pits. The latter class of coal contains the largest proportion of this danger ous gas, but holds it more tenaciously than do the steam coals, thus rendering the workings comparatively safer. It was found that, of the entire volume of occluded gas iu an anthracite, only one-third could be expelled at the tem perature of boiling water, and that the whole quantity, amounting to 650 cubic feet per ton, was only to be driven out by a heat of 300 C. Steam coals being softer and more porous give off enormous volumes of gas from the working face in most of the deep pits, many of which have been the scene of disastrous explosions. The gases evolved from the sudden outbursts or blowers in coal, which are often given off at a considerable tension, are the most dangerous enemy that the collier has to con tend with. They consist almost entirely of marsh gas, with only a small quantity of carbonic acid, usually under 1 per cent., and from 1 to 4 per cent, of nitrogen. Fire-damp when mixed with from four to twelve times its volume of atmospheric air is explosive ; but when the proportion is above or below these limits, it is inflam mable, burning quietly with a pale blue flame. When a lighted candle is exposed in a non-explosive mixture of this gas, the flame gradually elongates, forming a conical cap, floating above the wick, which may be extinguished by cautious withdrawal without communicating the fire to the surrounding atmosphere. This method of testing for gas in the working places and wastes, which is obviously only to be trusted in skilled hands, used to be commonly practised, but since the introduction of safety lamps it has fallen into disuse. The principle involved in the construction of safety- Safe lamps consists in surrounding the flame of a lamp by lami a protecting metal case, perforated with numerous small holes, through which the air for feeding the flame may freely enter, and the products of combustion pass out, while the passage of flame, or gases sufficiently heated to cause the ignition of the external air when laden with explosive gases, is prevented. In 1816 Sir Humphrey Davy made the great discovery that these conditions are fulfilled by the use of tubes reduced to a mere section, such as the apertures in wire gauze, when the substance of the wire is rightly proportioned to the size of the aperture. The standard adopted as the limit for safety at that time was a gauze of 28 iron wires to the linear inch, having 784 apertures per square inch, which has been used ever since. The common safety or Davy lamp consists of a small cylindrical oil lamp, covered with a cylinder of wire gauze about 6 inches long and 1J inches in diameter, with a flat gauze top. The upper part of the gauze is doubled to prevent its being worn into holes by the products ot combustion, and the air for feeding the flame enters round the wick. The gauze is mounted in a cage, consisting of three upright wires, screwed into a flat brass ring at each end. A handle is attached to the upper ring, while the lower one screws on to a collar on the oil-vessel of the lamp. When the two parts are screwed together the lamp is locked by a bolt passing through both parts, which is screwed down flush with or below the surface of the outer ring, so that the gauze cannot be removed without the use of a key. In Stephenson s safety-lamp, generally known as the " Geordie," from the inventor George Stephenson, the light is covered by a glass chimney, surrounded by an outer casing and top of wire gauze. The feed air is admitted through numerous small holes in a copper ring a little below the level of the wick. This is one of the safest forms of lamp, but requires considerable care in use, espe cially in keeping the small feed holes clear from dust and oil ; the glass protects the gauze from becoming overheated, SAFETY LAMPS.] COAL and when the air is dangerously charged with gas the light is extinguished. Various forms of safety-lamps have been introduced at different times, for the purpose of increasing the amount of light by substituting a glass cylinder for the lower portion of the wire gauze. The oldest of these is that of Dr Clanny, contemporary with those of Davy and Stepheuson. The air for supplying the flame, entering at the bottom of the gauze, and passing down the iiner side of the glass, protects the latter to some extent from becoming over heated, but a large amount of light is lost; by absorption in the glass, so that there is no great advantage over the ordinary Davy lamp to compensate for the extra weight and cost, especially as the safety property of the lamp depends upon the glass cylinder, which may be readily broken when subjected to the ordinary accidents of work ing. A more perfect form of lamp of the same character is that of Museler, which is extensively used in Belgium. It differs from Clanny s lamp by the addition of a conical chimney above the flame, which produces a rapid draught, and consequently a more perfect cooling of the glass cylinder by the down-draught of feed air for the flame. Boty s lamp, which was recommended by a commission of the Belgian Government as being safe in use, is essen tially that of Dr Clanny with Stephenson s perforated ring for admitting air at the level of the wick. Another Belgian variety is that of Eloin, in which the glass is shaped to the surface produced by the revolution of a parabolic arc, so as to disperse the light in parallel lines. The air is admitted by a Stephenson ring, combined with an Argand cap, the glass being surrounded by a brass chimney with a gauze top. In another form of the same lamp Museler s chimney is added. The locking of safety-lamps, so as to render them in capable of being opened by the miners when at work, is a point that has given play to a large amount of ingenuity. One of the most favourite devices is a combination of the wick-holder with the locking bolt, so that the latter cannot be withdrawn without lowering the wick and extinguishing the flame. Another method consists in the use of a lead rivet, uniting the two parts of the lamp, impressed with a seal, which cannot be removed without defacing the device. All this class of contrivances have the defect of only being efficacious when the miners are not provided with matches, or other means of obtaining a light. A more physically perfect method is that adopted by Bidder, where the locking bolt is magnetized and held in place by a force which can only be overcome by the application of a battery of heavy and powerful steel magnets. These are kept in the lamp cabin at the pit bottom, where the lamps are cleaned and served out lighted to the miners at the com mencement of the shift, and are collected before they return to the surface. When a Davy lamp is exposed to an atmosphere con taining less than 8 per cent, of marsh gas, the flame lengthens and becomes smoky ; when that amount is reached the flame returns to its usual size, but a column of blue flame rises to the top of the gauze. With 10 per cent, the flame of the wick is extinguished, the whole of the space within the gauze being filled with a blue flame of burning gas. If the lamp is allowed to remain too long in a fiery atmo sphere it becomes dangerous, as the gauze being heated to redness may fire the gas. The safety of the lamp is also endangered by an exposure to a current of gas moving at the rate of more than 6 or 8 feet per second, as the flame can then be readily driven through the gauze. It is there fore usual to protect the flame by a sliding shield of tin plate, horn, or mica from the direct action of any sudden outburst of gas in the workings. Lamps with glass cylin ders are generally very safe, except from the risk of acci dental breakage, which, however, is less frequent than might be imagined, and those taking air through a feed ring, such as Stephenson s, are readily extinguished in a foul atmosphere. The danger arising from gas in the workings may be considerably increased by the presence of coal dust in the air. This point has been the subject of investigation by Galloway, who found that an explosion may be produced by ignited particles of coal dust through the agency of a safety-lamp which under ordinary circumstances would be perfectly trustworthy. At Blanzy, in France, several fatal explosions have been traced to the firing of coal dust from the flame of a shot, even in cases where no fire-damp was present in the workings. An electric lamp, where the light is obtained from the Electric discharge in a Geissler vacuum tube, has been proposed amps, by Benoit-Dumas, instead of the ordinary safety lamps, or for use in exploring after explosions or in bad air ways. This consists of a box containing a galvanic battery, con sisting of two Bunsen cells, and a small induction coil, with connecting wires which convey the current to the lamp. The Bunsen cells may be conveniently replaced by a single bottle-ishaped bichromate battery. The cost and complication of this apparatus must necessarily limit its use. Apparatus, originating in France, known as aerophores, Aero- which enable the miner to carry sufficient fresh air for i llores - his own respiration, and to keep a lamp alight for a short time in a totally irrespirable atmosphere, have of late years come into use for the purposes of saving life after explosions, and repairing shafts and pit-work under water. There are two principal patterns, those of Galibert and Denayrouze. The former, which is the simplest, con sists of an air- tight bag of about 12 cubic feet capacity, con taining air at a little above atmospheric pressure, which is carried on the miner s back like a knapsack. The air, after being used, is returned with the products of respiration into the bag, and can be used over again until it becomes too impure for further use. It is obvious, therefore, that such an apparatus must be of very limited application, but its simplicity and cheapness are points in its favour for use in sudden emergencies. The Denayrouze apparatus consists of a series of sheet metal cylinders, containing air compressed to 300 or 350 S> to the square inch, which can be carried on the back, and served out at a pressure very slightly above that of the atmosphere by means of a reducing valve, whose construction is essentially the same in principle as that of the ordinary pressure regulator used in gas-works, i.e., a conical plug closed against its seat by the pressure of the air in the reservoir, which is constantly opposed by an external force tending to open it. This force is supplied by a disc of vulcanized india-rubber, which opens the valve at each inspiration, and allows a fresh supply of air to escape into the chamber of the regulator through the small aperture of the valve. Of course, all communication with the external air must be cut off, so that respiration can only take place through the mouth, the air-tube being attached by an india-rubber mask called a mouth-closer, and the nostrils closed by a spring clip. A similar regu lator valve, so constructed as to keep tlic india-rubber spring under a slight excess pressure in order to maintain a flow of air, is in connection with the lamp. This is of the ordinary Museler construction, with the addition of a chamber outside the gauze to receive the products of com bustion, which are discharged through a conical valve at the top, a reflux of the exterior gases being prevented by the pressure of a counter spring. The air is carried to the lamp by an india-rubber tube, which is sufficiently flexible to allow a certain freedom of motion. The dis tance that an explorer can penetrate with this apparatus is obviously limited by the capacity of the air-cylinders. VT. 10 COAL [MINING. These have been made large enough to supply air to a man with a lamp for an hour, but this is an inconvenient size, being too large to be carried on the back. Fires in Underground fires are not uncommon accidents in coal mines, mines. In the thick coal workings in South Staffordshire the slack left behind in the sides of work is especially liable to fire from so-called spontaneous combustion, due to the rapid oxidization that is set up, when finely-divided coal is brought in contact with air. The best remedy in such cases is to prevent the air from gaining access to the coal by building a wall round the burning portion, which can in this way be isolated from the remainder of the working, and the fire prevented from spreading, even if it cannot be extinguished. When the coal is fired by the blast of an explosion it is often necessary to completely isolate the mine by stopping up the mouths of the pits with earth, or in extreme cases it must be flooded with water or carbonic acid before the fire can be brought under. There have been several instances of this being done in the fiery pits in the Barnsley district, notably at the great explosion at the Oaks colliery in 18G6, when 360 lives were lost. Methods of The drawing or winding of the coal from the pit bottom winding, to the surface is one of the most important operations in coal mining, and probably the department in which me chanical appliances have been brought to the highest state of development. In the simplest case, where the mine is worked by levels, the trains of coal may be drawn from the working faces directly to the level mouth by horse power, or in some exceptional cases locomotives worked by com pressed air are used. In South Wales the power for lifting the load in the shaft is still in some small workings fur nished by a water balance, that is, a box which is filled with water at a high level, and in descending raises the loaded trucks by a rope passing over a pulley at the surface. This method is only available when there is a free drainage level for the water to run off w r hen the box reaches the lowest point. Other hydraulic motors, such as wheels, pressure engines, &c., are used in different locali ties as well as animal power, where the amount of coal to be drawn is small, but as a general rule it is necessary to have recourse to steam power to maintain an adequate output. The old custom of drawing the coals in tubs or hutches (cu/at of the French miner), swinging freely from the end of the drawing rope, is now almost entirely super seded by the adoption of cages sliding between fixed guides, which allow the load to move freely up and down while checking lateral oscillation. This improvement, which is due to Mr John Curr of Sheffield, was originally intro duced in 1798, but made surprisingly little progress for nearly half a century. It was first brought into general use in the North of England, but in many of the smaller pits of the Midland counties the older custom prevailed until recently. The different elements making up the drawing arrange ments of a colliery are (1) the cage, (2) the shaft or pit fittings, (3) the drawing-rope, (4) the engine, and (5) the Cage. surface arrangements. The cage, as its name implies, consists of one or more platforms connected by an open framework of vertical bars of wrought iron or steel, with a top bar to which the drawing-rope is attached. It is customary to have a curved sheet-iron roof or bonnet when the cage is used for raising or lowering the miners, to pre vent them from injury by falling materials. The number of platforms or decks varies considerably ; in small mines only a single one may be used, but in the larger modern pits two, three, or even four-decked cages are used. The use of several decks is necessary in old pits of small sec tion, where only a single tram can be carried on each. In the large shafts of the Northern and Wigan districts the cages are made about 8 feet lon^ and 3 feet broad, being sufficient to carry two large trams on one deck. These are received upon a railway made of two strips of angle iron of the proper gauge for the wheels, and are locked fast by a latch falling over their ends. The guides or conductors in the pit may be constructed Gui of wood, in which case rectangular fir beams, about 3 by 4 inches, are used, attached at intervals of a few feet to buntons or cross-beams, built into the lining of the pit. Two guides are required for each cage ; they may be placed opposite to each other, either on the long or short sides the latter being preferable. The cage is guided by shoes of wrought iron, a few inches long and bell-mouthed at the ends, attached to the horizontal bars of the framing, which pass loosely over the guides on three sides. In some of the large collieries in Northumberland wrought iron guides have been adopted with advantage. They are applied on one side of the cage only, forming a complete vertical railway, light flange rails such as are used for the roadways underground being used instead of wooden rods and iron cross sleepers, with proper seats for the rails instead of wooden buntons ; the cage is guided by curved shoes of a proper section to cover the heads of the rails. Rigid guides connected with the walling of the pit are probably the best and safest, but they have the disadvan tage of being liable to distortion, in case of the pit altering its form, owing to irregular movements of the ground, or other causes, Wooden guides being of considerable size, block up a certain portion of the area of the pit, and thus offer an impediment to the ventilation, especially in up cast shafts, where the high temperature, when furnace ventilation is used, is also against their use. In the Wigan district, wire-rope guides have been introduced to a very considerable extent, with a view of meeting the above objections. These are simply wire-ropes, from f to 1 inches in diameter, hanging from a cross-bar connected with the pit-head framing at the surface, and attached to a similar bar at the bottom, which are kept straight by a stretching weight of from 30 cwt. to 4 tons attached to the lower bar. In some cases four guides are used two to each of the long sides of the cage ; but a more general arrangement is to have three two on one side, and the third in an intermediate position on the opposite side. Many colliery managers, however, prefer to have only two opposite guides, as being safer. The cage is connected by tubular clips, made in two pieces and bolted together, which slide over the ropes. In addition to this, it is ne cessary to have an extra system of fixed guides at the surface and at the bottom, where it is necessary to keep the cage steady during the operations of loading and landing, there being a much greater amount of oscillation during the passage of the cage than with fixed guides. For the same reason it is necessary to give a considerable clearance between the two lines of guides, which are kept from 15 to 18 inches apart, to prevent the possibility of the two cages striking each other in passing. With proper precautions, however, wire guides are perfectly safe for use at the highest travelling speed. The cage is connected with the drawing-rope by short Ro] lengths of chain from the corners known as tackling clia chains, gathered into a central ring, to which the rope is attached. Round steel wire-ropes, about 2 inches in diameter, are now commonly used ; but in very deep pits they are sometimes tapered in section to reduce the dead weight lifted. Flat ropes of steel or iron wire were and are still used to a great extent, but round ones are now gene rally preferred. In Belgium flat ropes of aloe fibre are in high repute, being considered preferable by many colliery managers to wire, in spite of their great weight. In South Staffordshire, flat link chains made with three or more parallel links, with a stud of wood filling up the WINDING.] COAL hollow, are or were in general use in the numerous shallow pits working the thick coal in the neighbourhood of Dudley, &c. The best modern engines for drawing in collieries are usually direct-acting, with either horizontal or vertical cylinders. In the north of England a single engine with a heavy fly-wheel is often used, but the more general arrangement is to have two engines coupled to the opposite ends of the winding drum-shaft. In almost all cases steam is used at high pressure without condensation. The drum, when round ropes are used, is a plain broad cylinder, with flanged rims, and cased with soft wood packing, upon which the rope is coiled ; the breadth is made sufficient to take the whole length of the rope at two laps. One drum is usually fixed to the shaft, while the other is loose, with a screw link or other means of coup ling, in order to be able to adjust the two ropes to exactly the same length, so that one cage may be at the surface when the other is at the bottom, without having to pay out or take up any slack rope by the engine. For flat ropes, the drum or bobbin consists of a solid disc, of the width of the rope fixed upon the shaft, with numerous parallel pairs of arms or horns, arranged radially on both sides, the space between being just sufficient to allow the rope to enter and coil regularly upon the preced ing lap. This method has the advantage of equalizing the wark of the engine throughout the journey, for when the load is greatest, with the full cage at the bottom and the whole length of rope out, the duty required in the first revolution of the engine is measured by the length of the smallest circumference ; while the assistance derived from gravitating action of the descending cage in the same period is equal to the weight of the falling mass through a height corresponding to the length of the largest lap, and so on, the speed being increased as the weight diminishes, and vice versa. The same thing can be effected in a more perfect manner by the use of spiral or scroll drums, in which the rope is made to coil in a spiral groove upon the surface of the drum, which is formed by the frusta of two obtuse cones {laced with their smaller diameters outwards. This plan, though mechanically a very good one, has certain defects, especially in the possibility of danger resulting from the rope slipping sideways, if the grooves in the bed are not perfectly true. The great size and weight of such drums are also disadvantages, as giving rather unmanageable dimensions in a very deep pit. The use of a counterbalance chain for the winding engines is common in the collieries of the Midland dis tricts of England. In this method a third drum is used to receive a heavy flat link chain, shorter than the main drawing-ropes, the end of which hangs down a special or balance pit. At starting, when the full load is to be lifted, the balance chain uncoils, and continues to do so until the desired equilibrium between the working loads is attained, when it is coiled up again in the reverse direc tion, to be again given out on the return trip. The surface arrangements of a modern colliery are often of considerable extent and complexity, the most important feature being the pit-frame carrying the guide-pulleys or rope-rolls which lead the drawing-ropes from the verti cal line of the pit to the engine-drum. This consists essentially of an upright framework, carefully braced together, and strutted by diagonal beams against the wall of the engine-house, or other solid abutment. It is gene rally necessary to have a clear head-room, 10 or 20 feet or more, for the working arrangements at the surface above the level of the ground, especially in flat countries ; the pit- frames are made of considerable height, from 50 to 70 feet being not uncommon ; and when, as is generally the case, they are made of wood, they afford opportunities for the exercise of skilful carpentry. Of late years, however, wrought iron pit-frames have been adopted to some extent, which allows of a comparatively simpler construction being used, the main elements of the frame consisting of hollow latticed pillars and beams, similar to the construc tion now generally adopted for the pillars of railway signals, but of course of a more solid construction. They have one great advantage over wooden frames, in not being liable to destruction by fire, an accident which has occasionally happened with the latter. The guide-pulleys for iron or steel wire-ropes are made of very large dimen sions, to avoid strain upon the wires by sudden change of direction when moving at a high speed. The usual construction is a deep channeled rim or tire of cast-iron, from 7 to 20 feet in diameter, supported by numerous thin wrought iron arms, inclining inwards from a central cast iron boss, a form combining rigidity with comparative lightness. They are in fact very similar to the driving wheels of the large modern bicycles, supposing a channeled rim to be substituted for the india- rubber tire. To prevent accidents from the Safety breakage of the rope on the shaft, catches. or from overwinding when the engine is not stopped at the right moment, whereby the cage may be C Fig. 21. FIGS. 19-21. White and Grant s Safety Catch. dragged up to the head pulleys (both which kinds of acci dent are unhappily not uncommon), various forms of safety catch and disengaging hooks have been proposed. These consist of variously-constructed toothed levers, cams, or eccentrics, mounted upon transverse axes, attached to the top of the cage, whose function is to take hold of the guides, and support the cage in the event of its becoming detached from the rope. They are generally applied by means of springs acting against the pull of the rope. Figs. 19-21 represent a form of safety catch, introduced some years since by Messrs White and Grant of Glasgow. The catches BB consist of partially toothed eccentrics, which when released are forced inwards against the wooden guide a by the coiled springs d d, as shown in fig. 21. When the rope is drawing, the catches are lifted by the 7(5 COAL [MIXING. pull of the chains attached to the pulleys c c, which turn the broad toothed portions outwards, and away from the guides. The connection with the rope is made by the slide bar C and spring catch h having a projecting trigger, which, if the cage is lifted too high, strikes against the cross-bar of the framing k, and detaches the cage, which is then left hanging by the catches to the guides in the pit. The use of safety catches is more common in the collieries of France, Belgium, and Germany than in Eng land, where they are not generally popular, owing to their uncertainty in action, as they are often fouud to fail when most wanted. The constant drag of the catches on the guides when the rope slacks is also objectionable, but this has been overcome to a great extent in a very in genious contrivance invented by Mr Calow, where the catches are not brought into action unless the cage is actually falling clear of the rope, with a certain acquired momentum of its own. The only real safeguards against accidents in winding are to be found in constant vigilance, in maintaining the ropes in working efficiency, and in the use of proper signals and brake power in the engine house. The speed attained by the load in the shaft in the best- appointed English collieries is very considerable, and may be paralleled with that of a fast railway train. At Shire- oaks Colliery, Nottinghamshire, the cage with a load of 34 cwts. of coal in five tubs, and weighing in all 60 cwts., or with the rope at the bottom 92^ cwts., is raised from a depth of 51 G yards in 45 seconds, corresponding to an average of 35 feet per second, or 24 miles per hour, the maximum speed when the load is mid- way being 50 feet per second, or nearly 35 miles an hour. The ropes used are round, of steel wire, weighing 13 Ibs. to the yard, winding on to a spiral drum, increasing from 17 to 20 ftet in diameter. Thera are two engines with vertical cylinders, 32 inches diameter and 6 feet stroke, developing a useful effect of about 320 horse-power. The guide pul leys are 12 feet in diameter. The above may be taken as a good example of the mo dern class of winding engines, such as are required to draw from 600 to 1200 tons in the shift of 10 hours. When the pits are of small depth it is better to increase the weight of the load than to draw at a very high speed, as the loss of time in filling and unloading or striking the cages is the same for a short as for a long journey, so that it becomes advantageous to diminish the number of journeys for a given quantity of coal drawn. The great amount of dead weight required to be raised in the ordinary system of winding (e.g., in the instance given above, the total weight moved is nearly four times that of the nett load drawn, that of the ropes being nearly 1 1 times as much as the latter), has led to the proposal of various plans to obtain a more mechanically economical method, but none of these have at present been brought into successful use. One of the latest is that of M. Blanchet, who proposes to draw a number of tubs linked together into a long vertical train in a closed tube about 5 1 feet in diameter, by exhausting the air above them in the manner adopted in the pneumatic tubes used for the transmission of parcels. An experimental apparatus of this class has been recently constructed at Creusot, in France, designed to lift a cage with 9 tubs, attached to a piston, weighing in all about 12| tons. Striking When the cage arrives at the surface, or rather the plat- ail( j " form forming tho working top above the mouth of the pit, scrcening.it is received upon the keeps, a pair of hinged gratings which are kept in an inclined position over the pit-top by counterbalance weights, so that they are pushed aside to allow the cage to pass upwards, but fall back and receive it when the engine is reversed. The tubs are then removed or struck by the landers, who pull them forward on to the platform, which is covered with cast-iron plates; at the same time empty ones are pushed in from the opposite side. The cage is then lifted by the engine clear of the keeps, which are opened by a lever worked by hand, and the empty tubs start on the return trip. When the cage has several decks, it is necessary to repeat this operation for each, unless there is a special provision made for load- ipg and discharging the tubs at different levels. An arrangement of this kind for shifting the load from a large cage at one operation has recently been introduced by Mr Fowler at Hucknall, in Leicestershire, where the trains are received into a framework with a number of platforms cor responding to those of the cage, carried on the head of a plunger movable by hydraulic pressure in a vertical cylinder. The empty tubs are carried by a corresponding arrangement on the opposite side. By this means the time of stoppage is reduced to a minimum, 8 seconds for a three-decked cage as against 28 seconds, as the operations of lowering the tubs to the level of the pit-top, discharging, and replacing them are performed during the time that the following load is being drawn up the pit. The tub when brought to the surface, after passing over a weigh-bridge, where it is weighed and tallied by a weigher specially appointed for the purpose by the men and the owner jointly, is run into a tipping cage, and the contents are dis charged into an inclined screen with bars about 1 inch to 1 -| inches apart. The large coal remaining passes through a spout into a railway waggon placed below, the discharge being regulated by a valve at the lower end. The small coal passing through is either sold as such, or may be lifted by an elevator to a second series of screens, either fixed or rotating, with half-inch apertures. These make a further separation of larger pieces, which are sold as "nuts," while the small, or slack, passing through is sent to the coke ovens, if the quality of the coal is suitable. Asa rule, non- caking coals are not very closely screened, as the small is of comparatively little valu?, and therefore must have a proportion of larger sizes mixed with it to form saleable slack. Figs. 22-24, representing the surface arrangements Illustr adopted at a pair of pits in the Wigan district, may be tions f taken as fairly representative of the fittings of a large ^ ra ^ ( modern colliery, where a considerable output of coal has to men t 8 . be screened and loaded in an ordinary working day of less than twelve hours. The details, of course, will vary, ac cording to the nature of the outlet or vend, which may be by retailing into carts sent by purchasers, or by canals or railways, or by a combination of all three. In the example selected, the coal is loaded directly from the screens into full-sized trucks, each carrying from 6 to 8 tons, on a main line of railway. Of the two pits, one is an upcast, and is surmounted by a chimney at the surface, the drawing being confined to the downcast, which is 310 yards deep and 10| feet in diameter. GOO tons of coal are drawn from this depth in 10 hours by a pair of direct-acting engines, with vertical cylinders working a spiral drum, in creasing from 13i feet to 1 7| feet in diameter. The pit-head frame is of wood, with guide pulleys 7 feet in diameter, a much, smaller size than is now usually adopted ; the iron wire drawing-ropes are round, weighing 5 ft) to the yard. Double-decked cages of a light construction in wrought iron are used, carrying four tubs at a time. The landing platform is raised upon pillars 20 feet above the surface of the ground, and covered with iron plates. As soon as the cage arrives at the surface, the tubs are run into tumbling cages, which discharge their contents on to fixed screens, witL bars of 1 to 1^ inch aperture. The large coal passes by a shoot directly into the railway waggon, while the first screenings fall into a channel below, which is traversed by a series of scrapers attached to an endless chain, and are SURFACE ARRANGEMENTS.] COAL t carried to an elevator or Jacob s ladder, and discharged into rotatory drum sieves of about ^-inch aperture, pro ducing a second size of saleable coal, known as nuts, and FIG. 22. Elevation. FIG. 23. Plan. FIG. 24. Transverse Elevation. Fias. 22-24. Surface arrangements of Colliery. slack, which is sent away to the coke ovens attached to the colliery. The whole of the labour required in the screening the output of 600 tons in the day of ten hours is performed by one engineman, who has charge of all the mechanical arrangements, and nine boys, who pick out any large lumps of stone from the coal as it passes the first screens. The engine driving the screens and elevators is in charge of a special engineman. Fig, 25 represents one of a pair of pits at Pemberton Colliery, near Wigan, having the pit frames constructed in wrought iron lattice truss-work instead of wood. The screens for large coal (S) are arranged symmetrically on the landing platform, three on each side of the pit top, and discharge directly into waggons on the railway below. The small coal from these screens is passed by a screw creeper C, like those used in flour mills, to a bucket elevator E, which delivers it at the top of the second set of screens R, where the nuts and slack are separated. The platform, as in most of the new collieries in this district, is roofed over to protect the workmen from the weather. The second pit, which occupies a corresponding position on the oppo site side of the engine-house, is in every respect similar. The large collieries in the steain-coal district of North umberland are among the most productive ; thus, at Bed- lington, near Morpsth, 1200 tons are raised daily, and at North Seaton from. 1500 to 1800 tons. When the coal is very much mixed with shale, the slack Coal- often contains so much mineral matter as to be quite worth- washing less, until at least a partial separation has beeu effected. maclunes - This is now done by means of coal-washing machines, which were first adopted in France, but have now become general in other countries. There are many different forms, but the most usual is a fixed sieve plate, upon which the slack is received and subjected to the action of a current of water forced through the holes by the action of a fast-moving short-stroke plunger pump, which puts the Elevation tfvr /m 1 1 r 3 3 [ R 3 c Fro. 25. Surface arrangements, Pemberton Pit, Wigan. whole of the materials into suspension, and allows them to fall through the water at each stroke. By this means the coal, being the lighter material, travels to the surface, and the heavier shale and stone going to the bottom are dis charged through a valve there. The apparatus is in fact a form of the hydraulic jigging hutch used for the dressing of lead and other ores, except that in this case the lighter and not the heavier part is the valuable mineral. In another form of coal-dressing machine introduced by Mr Evrard, the jigging action is produced by a jet of steam acting directly upon the water instead of a plunger piston. Washed slack when suitable is used for conversion into coke, but in France and Belgium it is now generally employed in the production of agglomerated fuel, or bri quettes, or what is usually known in England as patent fuel. These consist of coal dust mixed with a sufficient amount of gas-pitch to be moulded into coherent bricks or cylinders, which are afterwards dried at a high tem perature, but below the point of carbonization. The con solidation of the slack may also be effected by the use of starch or dextrine, or even by cement or clay. This class of fuel is much used upon the French railways, being con venient for stowage and economical in use; but as a rule it is disagreeable to the passengers from the large amount of coal-dust carried off by the exhaust steam, and the unpleasant vapours produced by the burning pitch. The principal production of patent fuel in Britain is in South Wales.

The anthracite coal of Pennsylvania is subjected to the exceptional treatment of breaking between toothed rollers, and an elaborate system of screening before it is fit for sale. The largest or lump coal is that which remains upon a riddle having the bars four inches apart; the second, or steamboat coal, is above 3 inches; broken coal includes sizes above 2½ or 2¾ inches; egg coal, pieces above 2¼ inches square; large stove coal, 1¾ inches; small stove, 1 to 1½ or 1⅓ inches; chestnut coal, ⅔ to ¾ inch; pea coal, ½ inch; and buckwheat coal, ⅓ inch. The most valuable of these are the egg and stove sizes, which are broken to the proper dimensions for household use, the larger lumps being unfit for burning in open fire-places.

Proportion of coal obtained in working.The proportion of coal utilized in the working, as compared with the total contents of the seam, varies very considerably in different districts, being greatest in seams of moderate thickness, from 3 to 5 feet, which on the long-wall system can be entirely removed. In thick coals, such as the ten-yard seam of South Staffordshire, the waste is very considerable. In Cheshire and Lancashire about 1330 tons of saleable coal are obtained from an acre for each foot of thickness in the seam, only 8 per cent. of the total being left behind in the workings.

At Dowlais, on the north of the South Wales coal-field, the yield is 1190 tons to the foot by long-wall, but only 866 tons when the same seam was worked by the pillar and stall system; but on the south side of the basin, where the seams lie at a steep slope, the loss is often much greater, being from 20 to 50 per cent, on pillar and stall workings. In the Barnsley district, the yield is from 1150 to 1280 tons in thick seams, and a maximum of 1417 tons has been obtained in a thin seam, the solid contents of the whole coal being estimated at 1556 tons per foot per acre. In Northumberland about 1200 tons are got out of a total of 1300. In the thick coal of South Staffordshire, from 12,000 to 16,000 tons per acre are got at the first working on an average thickness of 25½ feet, or about 640 tons to the foot, or from 50 to 60 per cent, of the whole, which is increased by the second and third working to 70 or 75 per cent., making a loss of from 25 to 30 per cent. This amount is reduced, however, by the long-wall method of working.

Probably from 10 to 15 per cent. may be taken as the unavoidable loss in working under the most favourable conditions, but in many cases the proportion is considerably higher.

Ownership of coalIn the United Kingdom the ownership of coal, like that of other minerals, is in the proprietor of the soil, and passes with it, except when specially reserved in the sale. The greater number of collieries are worked upon leases, the rents or royalties being variously charged in different localities. A minimum reserved rent to cover a certain output, with a rate per ton on any quantity in excess, is the most general practice; but in Lancashire and Yorkshire the royalties are charged at a fixed rate per acre per annum upon each seam worked, and in South Staffordshire at a proportion (from ${\tfrac {1}{6}}$ to ${\tfrac {1}{16}}$) of the coal at the pit's mouth.

Coal lying under the sea below low-water mark belongs to the Crown, and can only be worked upon payment of royalties, even when it is approached from shafts sunk upon land in private ownership.

In the Forest of Dean, which is the property of the Crown as a royal forest, there are certain curious rights held by a portion of the inhabitants known as the Free Miners of the Forest, who are entitled to mine for coal and iron ore, under leases, known as gales, granted by the principal agent or gaveller representing the Crown, in tracts not otherwise occupied. This is the only instance in Great Britain of the custom of free mining under a Government grant or concession, which is the rule in almost every country on the Continent.

Coal Mines Regulation Act.The working of collieries in the United Kingdom is subject to the provisions of the Coal Mines Regulation Act of 1872, 35 and 36 Vict. cap. 76, which is administered by inspectors appointed by the Home Office, and forms a complete disciplinary code in all matters connected with coal-mining. Among the chief provisions of the Act are the following:—

1. Females and boys under 10 are not allowed to work underground.
2. Boys between 10 and 12 are not allowed to work except in thin mines.
3. No boy under 12 to drive a gin horse, or under 18 a steam-engine.
4. Wages not to be paid at public-houses.
5. Working of mines by a single shaft prohibited.
6. Managers to be certificated as competent by a board of examiners.
7. Annual return of coal wrought to be made to Inspectors.
8. Notice of accidents to be sent to Inspector.
9. Openings of abandoned workings to be fenced.
10. Plans to be kept up to within six months of date.
11. Plans of abandoned mines to be deposited with Home Office.
12. General rules for the safety of miners in fiery mines, management of ventilation, safety lamps, and gunpowder, protection against accidents in shafts and levels, &c.
13. Power to frame special rules subject to approval of the Secretary of State.

Breaches of the provisions of the Act are punishable by fine and imprisonment by a court of summary jurisdiction, subject to appeal to the Quarter Sessions, or to the Circuit Court in Scotland.

The relation between the number of hands employed and the output of collieries varies considerably in different districts, being highest in those where the coal is moderately thick, soft, easily cut, regularly shaped, and with a good roof, and least in faulted and disturbed seams, and those with a bad roof, where the accessory operations of timbering and driving stone drifts require the employment of a large proportion of the working staff on non-productive work, i.e., other than cutting coal. The following figures give the relative force employed above and below ground in two large steam-coal collieries in South Wales, each producing about 500 tons per day:

Colliers cutting coal	225	200
Other underground hands	229	174
Surface hands	43	36
	497	410

showing in the one case an average of about 1 ton, in the other about 1¼ ton per hand per day, but if the hands cutting coal be alone considered, the amount is about the same in both cases, or a little over two tons per day.

The annual output per man on the total force employed in several of the principal European coal-fields has been computed as follows:

Newcastle	315 tons per man per annum.
Westphalia	215 tons per man„ per annum.„
Saarbrücken	170 tons per man„ per annum.„
France—Loire	200 tons per man„ per annum.„
France—„Nord	149 tons per man„ per annum.„
Belgium—Charleroi	147 tons per man„ per annum.„
Belgium—„Mons	124 tons per man„ per annum.„

These figures refer to some years back, and are probably not quite accurate at the present date, as the amount of work done by the individual collier has sensibly decreased in most countries. It will be seen that the output is smallest in the thin disturbed measures of the Franco-Belgian coal-field.

In Prussia in 1874, with an output of 33,000,000 tons of coal and 8,000,000 tons of lignite, the average per ACCIDENTS-, i C A L underground hand was about 243 tons for the former and about 600 tons for the latter. The larger comparative yield in lignite mines is due to the fact that a very large proportion are worked as quarries. The annual production of coal throughout the world may be roughly estimated at about 260 millions of tons for 1874, which quantity includes about 17 million tons of lignite and coal from formations newer than the coal measures in Europe. Nearly one-half of the total is raised in the United Kingdom, the approximate quantities of the different countries being as follows : Tons. United Kingdom 125,000,000 United States of America 48,000,000 Germany 35,000,000 Lignite, 9,000,000 Belgium 17,000,000 France 17,500,000 320,000 Austria 4,700,000 ,, 5,700,000 New South Wales 1,300,000 Russia 1,000,000 Spain India Smaller European States. British North America . . . Chili Other Australian Colonies 30,000 50,000 750,000 700,000 125,000 105,000 750,000 200,000 50,000 There is no trustworthy information as to the produce of China and Japan, but these probably do not exceed 100,000 tons. In the larger coal-producing European countries the output was very high in 1873, the following year having shown a slight falling off, but in America the annual increase was maintained. According to the official mineral statistics, the produce of coal in the United Kingdom for the years 1873, 1874, 1875, classified according to districts, was as shown in the following table, from which it will be seen that the check in 187^ was followed by great increase of production in 1875 : 1873. 1874. 1875. N Durham Tons. Tons. ( 6,180,000 Tons, Northumberland Cumberland 1 12,204,340 1,747,064 | 6,463,550 1,102.267 , 12,640,789 1,226,737 Westmoreland 1,972 1,200 S. Durham 17,436,045 17,900,250 19,456,534 Yorkshire 15,311,778 14,812,515 15,425,278 Derbyshire ( 7,150,570 7,091,325 Nottinghamshire Leicestershire 11,568,000 ) 3,127,750 ) 1,100,465 3,250,000 1,154,619 Warwickshire 851,500 799,750 S. Staffordshire Worcestershire | 9,463,539 8,389,343 9,251,791 Shropshire 1,570,000 1,187,950 1,229,785 N. Staffordshire Cheshire 3,892,019 1,150,500 4,313,096 615,105 4,496,213 658,945 N. and E. Lancashire W Lancashire 9,560,000 7,500,000 8,095,570 7,442,950 8,825,798 8,250,246 N. Wales 2,450,000 2,425,300 2,337,308 Gloucestershire ( 1,147,272 1,273,080 Somersetshire . ( 1,858,540 ( 609,684 654,878 Monmouthshire . 4,500,000 5,038,820 3,525,975 S.Wales 9,841,523 10,184,885 10,632,597 Scotland E. 10,142,039 10,182,326 11,419,619 Do. W 6,715,733 6, 606, y 35 7,177,888 Ireland 103,435 139,213 127,750 Total 127,016,747 125,067,916 131,908,105 Amount exported, including coke and patent fuel 12,748,390 14,045,325 14,544,916 Leaving for home ) consumption .. .. ) 115,268,357 111,022,591 117,363,189 Value at pit s mouth. . 47,629,787 45,848,194 43,969,370 The quantities of coal consumed by the different branches of manufacturing industry as well as for lighting, heating, and other purposes, was investigated by the Royal Com mission on Coal, from vol. iii. of whose Report, published in 1 870, the following summary is taken. The figures refer to the year 1869. Tons. Total quantity of coal raised 107,427,537 Do. exported 9,775,470 Leaving for home consumption 97,652,087 1. Coal used for iron manufacture .... , 32,446,606 2. Do. producing power and general manufacturing purposes. . . 26, 327, 21 3 3. Do. domestic purposes 18,481,527 4. Do. gas and water supply 7,811,980 5. Do. mines and collieries 7,225,423 6. Do. steam navigation 3,277,562 7. Do. railways 2,027,500 8. Do. smelting metals other than iron 859,231 9. Do. miscellaneous purposes 195,045 97,e;52 z OS7 The above quantities may be proportionally classified as follows : Mineral and metallurgical industries (1, 5, 8) 44 percent. Domestic consumption, including gas and water (3, 4) 26 ,, General manufacturing purposes (2) 25 ,, Locomotion by sea and land (6, 7) 5 ,, 100 Coal-mining is unfortunately a dangerous occupation, Accidents, more than a thousand deaths from accident being reported annually by the inspectors of mines as occurring in the collieries of the United Kingdom. The following table shows the number of lives lost during the last five years, classified according to the inspectors returns : Year. Explo sions of fire-damp. Falls of ground. Other under ground acci dents. Accidents in shafts. Accidents at sur face. Total. 1871 269 435 176 123 72 1075 1872 154 456 217 155 78 1060 1873 100 491 221 171 86 1069 1874 166 413 214 154 109 1056 1875 288 458 227 172 99 1244 The principal sources of danger to the collier, as dis tinguished from other miners, are explosion of fire-damp and falls of roof in getting coal, these together make up about 70 per cent, of the whole number of deaths. It will be seen that the former class of accidents, though attended with great loss of life at one time, are le.ss fatal than the latter. The great increase in the deaths from explosion in 1875, over the preceding year, is to be attributed to the Swaithe Main explosion at Barnsley on December 6th, when 143 lives were lost. The following return expresses the relation between the fatal accidents and the total number of miners employed, and the amount of coal raised for each death. The latter quantities are in some degree conjectural, being dependent upon estimated returns of produce, and are probably some what too large. Tear. 1 death for 1871 1872 1873 1874 1875 345 miners employed 394 479 ,, 510 430 109,246 tons coal raised 116,409 133,667 ,, ,, 133,251 ,, ,, 118,730 ,, ,, In Prussia, in the year 1874, there were 484 deaths from accidents, which corresponds to about three deaths per thousand hands employed, or, according to the above 80 COAL [ANALYSIS. classification, 1 in 334, with a produce of about G5,000 tons of coal for each death. It would appear, therefore, that the proportional loss of life, in the collieries of the United Kingdom, is less than that in foreign countries. Analysis of Assay and Analysis. The chemical examination of a coal. C oal may be cither complete or partial. When it is desired to obtain information as to the exact composition, the analysis is conducted in the same manner as the analysis of organic compounds by combustion with oxide of copper or chromate of lead in a hard glass tube, the carbonic acid and water formed being absorbed by solution of hydrate of potassium and dry chloride of calcium respec tively, and the proportion of carbon and hydrogen being calculated from the increase of weight in the tubes con taining the absorbing media. It is usual to operate upon a small sample (about 5 grains), which is very finely powdered and placed in a small trough or boat of platinum in the tube, the combustion being aided by a stream of oxygen from a gasholder. By this means the incombustible residue or ash is left in a condition for weighing, being free from admixture of foreign substances. Sulphur is determined by the fusion of a weighed quantity with a mixture of salt and nitrate of potassium in a platinum vessel, producing sulphate of potassium, which, on the addition of a salt of barium, is precipitated as sulphate of barium. Care must be taken to perform the operation over a flame free from the vapour cf sulphur com pounds, which may vitiate the result by apparently increas ing the amount of sulphur present. For this reason, the flame of a spirit lamp is to be preferred in making the fusion to that of coal gas, which is rarely free from sulphur coin- pounds. Sulphur existing in the form of gypsum or sul phate of calcium may be removed by washing a sample with boiling water, and determining the sulphuric acid in the solution. The washed sample is then fused with nitre in the usual way to determine the proportion of sulphur existing as iron pyrites. This distinction is of importance in the examination of coals intended for iron smelting, as the sulphates of the earthy metals are reduced by the gases of the furnace to sulphides, which pass into the slag without affecting the quality of the iron produced, while the sulphur of the metallic sulphides in the ash acts pre judicially upon the metal. The difference between the original weight of the sample and that of the carbon, hydrogen, sulphur, and ash, after making allowance for hygroscopic water, is attributed to oxygen and nitrogen, which are not directly deter mined. The character of the ash affords some guide to the quality of the coal from which it is derived. Thus, a red tint is generally indicative of the presence cf iron pyrite s, and a light or white colour of its absence. Phosphorus if present will be found in the ash, and may be determined by the ordinary processes of analysis. A useful approximate method of determining the character of a coal is by ex posing a coarsely powdered sample of known weight, in a covered crucible, to a strong red heat as long as inflammable vapours are given off, when it is cooled and weighed. The loss of weight represents the volatile con stituents hydrogen, oxygen, and hydrocarbon gases, pro duced by destructive distillation, while the residual coke includes the ash, and is called fixed carbon. The character of the button of coke obtained is a good indication as to the caking or non-caking quality of the coal from which it is derived, and the amount of ash may be determined by burning it in a muffle or over the flame of a Bunsen burner, The fitness of a coal for gas -making is usually determined by operating upon a sample of a few pounds weight in a special apparatus which reproduces the pro- Besses of manufacture upon a small scale. One of the most important factors in the economic valuation of a coal, is the so-called calorific power or value, by which is usually understood the number of pounds of water at boiling point that can be evaporated by the complete combustion of one pound of coal. This may be obtained theoretically, when the composition of the coal is known, by computing the heating effect of the carbon and the disposable hydrogen ; but in the absence of an analysis, it may also be determined directly by several approximate methods. One of the most con venient instruments for this purpose is Thompson s calorimeter. This consists of a copper cylinder in which a weighed quantity of coal intimately mixed with chlorate or nitrate of potassium is deflagrated under a copper case like a diving-bell, placed at the bottom of a deep glass jar filled with a known weight of water. The gases produced by the combustion rising through the water are cooled, with a corresponding increase of temperature in the latter, so that the difference between the temperature observed before and after the experiment furnishes a mea sure of the evaporative power desired. The instrument is so constructed that 30 grains of coal are burnt in 29,010 grains of water, or in the proportion of 1 to 937, these numbers being selected that the observed rise of tempera ture iu Fahrenheit degrees corresponds to the required evaporative value in pounds, subject only to a correction for the amount of heat absorbed by ths mass of the instru ments, for which a special co-efficient is required, and must be experimentally determined. Another approximate method, due to Berthier, is based upon the reduction of oxide of lead by the carbon and hydrogen of the coal, the amount of lead reduced affording a measure of the oxygen expended, whence the heating power may be calculated, 1 part of pure carbon being capable of producing 34i times its weight of lead. The operation is performed by mixing the weighed sample with a large excess of litharge in a crucible, and exposing it to a bright red heat for a short time. After cooling, the crucible is broken and the reduced button of lead is cleaned and weighed. The re sults obtained by this method are less accurate with coals containing much disposable hydrogen and iron pyrites than with those approximating to anthracite, as the heat equivalent of the hydrogen in excess of that required to form water with the oxygen of the coal is calculated as carbon, while it is really about four times as great. Sulphur in iron pyrites also acts as a reducing agent upon litharge, and increases the apparent effect in a similar manner. The theoretical evaporative power of a coal found by either of the above methods is always considerably above that obtained by actual combustion under a steam boiler, as in the latter case numerous sources of loss, such as imperfect combustion of gases, loss of unburnt coal in cinders, &c., come into play, which cannot be allowed for in theoretical experiments. It is usual, therefore, to determine the value of a coal by the combustion of a weighed quantity in the furnace of a standard boiler, and measuring the amount of water evaporated by the heat developed. Various investi gations of this kind have been made at different times, both in Europe and America, the most extensive being the following : Johnson, Report on American Coals, Washington, 1844 ; De la Beche and Playfair, Three Reports on Coal suited to the Steam Navy, London, 1848-49-51 ; P. W. Brix, On the Heating Power of Fuel used in Prussia, Berlin, 1853 ; Hartig, Heating Power of Saxon Coal, Dresden, 1860. Tne following table of the average results obtained from these investigations shows the number of pounds of water evaporated for every pound of the different kinds of coal

burnt.

81 17 8-37 28 7.94 8 7-70 8 7-58 7 3-66 to 4-19 5 3 43 to 3 66 6 2-41 to 3-92 51 6-42 to 8-16 <D .. f S. Wales Average of 37 kinds, 9 05 tt> f|N. of England, K * < Lancasliire, ~& I Scotland, ft ^ Derbyshire, Wood, Peat, Lignite, Coal (Prussian),

The literature relating to coal and coal mining, is very extensive, but the following list includes the titles of the more important works upon these subjects.

England and America.—The Report of the Royal Coal Com mission (3 vols., fol., with Atlas, London, 1870). This is the most comprehensive work upon the subject. Hull, Coal Fields of Great Britain (3d ed. London, 1873). Reports and Maps of the Geological Surveys of the United Kingdom. Descriptive memoirs of each coal field published as completed. Percy, Metallurgy, vol. i., on Fuel (2d ed. London, 1875), containing full details of the chemistry of coal. Greenwell, Practical Treatise on Mine Engineering (2d ed. London, 1869). Andre, Practical Treatise on Coal Mining (London, 1876). Smyth, Coal and Coal Mining (2d ed. London 1872). Jevons, The Coal Question (2d ed. Lon don, 18C6). Rogers, Geology of Pennsylvania (2 vols., Edinburgh, 1850). Proceedings of the South Wales Institute of Engineering (8 vols., Merthyr, 1858-73). Transactions of the North of England Institute of Alining Engineers (1% vols., Newcastle, 1852-74). Various Geological Reports of the State an.d General Governments of the United States ; including Newberry s OhioReports, Cox s Indiana lie- ports, and Hayden s Reports of Geological Survey of the Territories.

France and Belgium.—Burat, Geologic de, la France (8vo. Paris, 1864). Cours d Exploitation de Mines (1871). Matiricl des Houilliercs en France, <L-c. (1861-68). Bulletin de la Societi de Vlndustrie Mineralc, S. Etienne (20 vols. since 1855). Ponson, Traiti de T Exploitation dcs Mines de Houillc (2d ed. Liege, 1868-71). Supplement to the above (1867-72). De Kuyper, Revue Universelk des Mines, <L~c. (Liege, since 1854).

Germany.—Geinitz, Die SteinJcohlcn Leutschlands, <L-c. (3 vols. 4to, Munich, 1865). This is the most complete book on the sub ject. Zinckcn, Die Bramikoldc (2 vols., Hanover, 1865-71). Zeitschrift fur Berg Hiittcn und Salinemvesen, <c. (4to. Berlin, 22 vols. since 1854).

(h. b.)