Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/68

Rh COAL [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 &quot;great seam&quot; 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 &amp;lt; 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 &quot;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,