Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/69

Rh 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 .,, &amp;lt; &amp;lt;! 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&quot; 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&amp;lt;%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.