Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/65

Rh 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