116
COAL
original dimensions. The evidence for this is to be seen in the large number of microphotographs in the memoir just referred to, which represents the result of twenty-one years’ work. Approximately the change of wood into coal, and the proportion of the valuable product eliminated, may be represented as follows :— 4(C6H10O5) = C9HgO + 7CH4 + 8C02 + 3H20. Cellulose. Coal. Methane. Carbon Water. dioxide. The solid product C9H60 corresponds to an average bituminous coal of the composition, carbon 83 T, hydrogen 4'6, oxygen 12'3 per cent., and represents about 20 per cent, of the original weight of cellulose and 45 per cent, of its heating power. Another aid to the study of the structure of coal has been found by H. M. Couriot {Annates de la Societe Geologique de Belgique, vol. xxiii. p. 105) in Rontgen photography, the carbonaceous or combustible portion being readily permeable by X-rays, while the mineral matter is comparatively opaque. In this way photographs showing the arrangement of the ash in parallel thin bands may be obtained from a piece of coal about an inch thick when exposed perpendicularly to the planes of bedding; included masses of iron pyrites appear as dark spots. The suggestion has also been made to use this agent as a means of determining the proportion of incombustible matter in coal, the sample being ground to powder and enclosed in a wooden box of a long, tapered wedge form, with a fluorescent screen along one side, which becomes sensitive to the rays passing through a greater or less thickness of the coal wedge in proportion to its freedom from mineral matter. According to Kotte {Stahl u. Eisen, vol. xx. p. 392), however, this method is unreliable for quantitative purposes, since for equal contents of ash the permeability varies with the nature of the mineral matter, a small proportion of iron being more effective in increasing the opacity than much larger amounts of the ordinary ash constituents, silica, alumina, &c. Thus for equal total amounts of ash, that containing the least amount of iron, 0'07 per cent., gave the clearest photograph, and that with 5‘4 per cent, the worst. The existence of coal-fields below the secondary strata in the south-east of England, along the line joining the Develop- South Wales and Westphalian basins, as meat of inferred by the late Mr Godwin Austen, has of coallate years been verified by the discovery of fields. carboniferous strata with workable coal seams below the chalk and other secondary formations in the vicinity of Dover, where in 1890 a borehole reached coal at a depth of 1180 feet from the surface, and in a further depth of 1042 feet several seams were subsequently proved of various thicknesses up to 4 feet. In another boring at Ropersole, between Dover and Canterbury, 1774 feet deep, the last 197 feet are in carboniferous strata with two coal seams. In the Dover sinking a bed of oolitic brown iron ore, resembling that of Cleveland and Luxemburg, has been discovered at a depth of 600 feet. Most extensive developments have also been made on the eastern side of the great Midland coal-field, and numerous pits have been sunk through the magnesian limestone and other overlying strata along the whole length of the basin, from Yorkshire to Nottinghamshire. At South Carr, near Gainsborough, in Lincolnshire, the regular succession of the seams in the coal-field has been proved under 1700 feet of New Red Sandstone rocks down to the Barnsley hard coal at 3186 feet, the greatest depth at which coal has as yet been proved in the United Kingdom. It has been suggested that the coal brought up by the trawlers on the fishing bank known as the Coal Pit in the North Sea, 65 miles east of the mouth of the Humber, may be derived from the eastern outcrop of the seams in this
basin, which, if this be the case, would be the largest coal-field in Europe. In the Rhenish Westphalian coal basin, the most important one in Continental Europe, great activity prevails both in exploration and opening of new mines. This is in many respects similar in structure to that of South Wales, a large number of seams, none very thick, being distributed through a great thickness of strata. These are folded transversely into three principal troughs whose axes have a general north-westerly strike, but with the important difference that the carboniferous strata are exposed for only a short distance along the southern margin, the greater part being covered by secondary and tertiary rocks, which increase in thickness rapidly to the north. The newer sinkings have therefore to pass through constantly increasing depths of water-bearing measures, with the result that special methods of overcoming such difficulties have been brought to a high degree of perfection in this region. According to Schultz {Mittheilungen uber den Niederrheinisch - Westfdlischen Steinlcohlen - Bergbau, 1901, p. 28) the proved area in 1900 was 1157 square miles, estimated to contain in workable seams :— Tons. Down to 700 metres (2300 feet) . . . 11,000,000,000 700 to 1000 metres (3280 feet) . . . 18,300,000,000 1000 to 1500 metres (4920 feet) . . . 25,000,000,000 Total within maximum working depth At greater depths
54,300,000,000 75,000,000,000
The development of the coal-fields of the newer mining regions can be best appreciated by the statistical table compiled by Mr B. H. Brough in the Journal of the Iron and Steel Institute :— Europe— Tons. 1900 225,170,360 United Kingdom . ,, 109,271,726 Germany, coal „ 40,279,332 ,, lignite . ,, 33,270,385 France 1899 22,072,068 Belgium ,, 11,455,139 Austria, coal „ 21,751,794 ,, lignite . „ 1,238,855 Hungary, coal ,, 4,292,584 ,, lignite. 1900 2,680,193 Spain . „ 13,104,000 Russia. 1899 212,973 Holland ,, 303,425 Bosnia, lignite ,, 78,000 Rumania, ,, 1896 11,726 Servia, ,, 1899 388,534 Italy, ,, ,, 239,344 Sweden, ,, Asia— „ 4,937,000 India . 1898 6,598,033 Japan . 1899 35,675 Borneo Africa— 1898 1,938,424 Transvaal . 1899 324,161 Natal . ,, 209,000 Cape Colony America — 1900 238,877,182 United States 1899 4,142,242 Canada ,, 113,191 Mexico 1898 10,000 Peru . Australasia— 1900 5,507,497 New South Wales 1899 494,000 Queensland . „ 262,380 Victoria ,, 54,000 Western Australia ,, 42,000 Tasmania . ,, 975,234 New Zealand In putting down new pits, while the methods formerly described are generally followed, much has been shaft, done towards accelerating the rate of work, sinking. In hard ground for instance, boring machines, supported on radial arms attached to a central pillar, are
