17 



COAL FORMATION. 



COAL FORMATION. 



13 



beds of calcareo-maenesian conglomerate. Great disturbances have 

 however interrupted the regularity of this arrangement, and caused 

 divisions of the coal-measures, which render it difficult to trace out 

 the exact dimensions of the field. At Disley, in Cheshire, it bifur- 

 cates into two branches, having an intermediate ridge or " saddle of 

 millstone grit, the eastern branch forming a trough, of which the 

 strata crop out on both sides against the millstone grit." This part of 

 the field is a long narrow strip joined to the main field at Disley, and 

 extending thence southward fifteen miles to near Mearbrooke in 

 Staffordshire. The strata of the western branch of this bifurcation, 

 extending from Disley to Macclesfield, dip again to the west, but not 

 at go great an angle as they rose, on the e::st side of the intermediate 

 ridge. In other parts of the coal-field great faults occur, but it has 

 not been sufficiently investigated by the geologist for them to be 

 distinctly traced. Mr. Bakewell has investigated a small portion, 

 which he distinguishes as the Coal-Field of Bradford : the result of his 

 observations is found in the second volume of the ' Geological Trans- 

 actions.' This tract is rather more than two miles long, and little 

 more than one mile and a furlong wide. It is situated on the river 

 Medlock, a short distance east-south-east of Manchester. It is sur- 

 rounded on every side, except the east, by the red-sandstone which 

 prevails in the environs of Manchester. Beds of limestone pass under 

 this and overlay the coal-measures, in which there are several beds of 

 coal rising to the north, under an angle of 30. One of these, near 

 the centre of the field, is four feet in thickness. To the north of these 

 inclined beds there is a considerable disturbance, and the direction of 

 the beds becomes suddenly vertical. One of the vertical beds, toge- 

 ther with its accompanying strata, bears so close a resemblance to the 

 4-foet coal above mentioned, that there is no doubt of their iden- 

 tity, and that the vertical stratum was, before the dislocation which 

 severed them took place, a continuation of the first. With these 

 vertical beds the coal-measurea terminate : on the north an interval of 

 the red-sandstoue succeeds for about 1400 yards, when coal-beds 

 again appear, rising as before towards the north. All this indicates 

 I'xn.'iderable faults and subsidences, which however cannot be accu- 

 rately traced at present. The coal from the Lancashire field supplies 

 Manchester, Liverpool, and the surrounding districts. 



6. The North Lancashire Coal-Field is one of little importance. It 

 lies midway between Lancaster and Ingleton ; it is about eight mil. H 

 long and six miles wide, but it has never been thoroughly examined, 

 and its strata cannot be distinctly stated. 



7. The Whitehaven Coal-Field is situated on the west coast of 

 Cumberland, and extends from near Egremont, -south of Whitehaven, 

 to near Allonby on the north. 



Central Coal District. Under this division are classed the coal- 

 fields of Ashby-de-la-Zouch, of Warwickshire, and South Staffordshire, 



1. The Coal-Field of Ashby-de-la-Zouch is of a very irregular figure, 

 and so much dislocated that it rather forms two small basins than 

 one continuous whole. The greatest length from north-west to south- 

 east is about ten miles, the greatest breadth about eight miles. The 

 eastern extremity of this area approaches almost close to the transition 

 d (strict of Charnwood Forest. This coal-field is described by Mr. 

 Farey as " one of the highly curious but perhaps not uncommon 

 occurrences in the red marl districts ; a tract entirely surrounded by 

 a fault, or a series of faults, which unite, seem lifted up through the 



i irl strata, and denudated, the coal strata having rapid dips in 

 various directions, while the surrounding strata of red marl are hori- 

 zontal, or as nearly so as may be." Of the two portions of the 

 field, one ranges by Ashby Wold, about three miles on the west 

 of Ashby ; the other by Cole Orton, which is about the same distance 

 on the east. 



The Ashby Wold portion ranges from Swepston, four miles south 

 of Ashby, to Bretby in Derbyshire : the inclination of the strata is 

 towards Ashby ; but between the out-crop of the beds and that town 

 another crop has been traced near Brothorpe, dipping in a contrary 



ion. More than twenty coal-works have been opened on this 

 line. The lowest shaft sunk is to the depth of 246 yards. One of 

 the seams is from 17 to 21 feet thick. Thisgreat thickness is caused, 

 it is supposed, by the running together of two or more seams a cir- 



';mce which is known to occur in the coal-fields of South 



rdshire. The eastern portion of this district commences about 

 a mile and a half north-east of Ashby, and extends about six miles in 

 length, running parallel to the larger portion. The strata dip to east- 

 north-^ast. In the pits belonging to Sir George Beaumont two coal- 



fach a yard and a half thick, are worked. On Cole Orton Moor 

 several coal-seams, which have been proved to lie above these, have 

 been worked at the depth of 1 1 6 feet. 



2. The Warwickshire Coal-Field commences at Wyken and Sow, 

 two villages about three miles east of Coventry, and continues in a 

 north-west direction to Polesworth and Wareston, about five miles 

 east of Tamworth, a distance of sixteen miles : its average breadth is 

 about three miles. All the strata ri*e to the east-north-east, the 

 inclination becoming greater towards the eastern edge of the field, 



in many parts it makes an angle of more than 45 with the 



i wards the west it decreases to about one foot in three, 



iitly in five. The principal collieries are near the south of the 



fi-1.1, at 'Jriff and Bedworth. The depth of the first is 117 yards, and 



tin' principal seam three yards in thickness. The same seams are 



KIT. ntsT. uiv. vol.. it. 



worked in the Bedworth mines, but there the fii-st and second coal- 

 seams of Griff run together and form a 5-yard seam. The interme- 

 diate strata of shale which separate them at Griff are found in the 

 eastern shaft to be 33 yards, and in the western 25 yards thick ; but 

 they gradually decrease as they proceed westward, till at length 

 they entirely vanish. 



3. South Staffordshire or Dudley Coal-Field, the principal in the 

 central district, extends from Beverton, near Badgely, on the north- 

 east, to near Stourbridge on the south-west. The greatest length is 

 about twenty miles, and its greatest breadth, from Walsall to Wolver- 

 hampton, is about seven miles, but it is very irregular towards the 

 south, being almost divided into two parts. The area, from actual 

 survey, has been found to be about sixty square miles. The southern 

 portion, extending from Stourbridge to Bilston, about seven or eight 

 miles in length and four in breadth, has been fully investigated by 

 Mr. Ken's, and described by him in Shaw's ' History of Staffordshire.' 

 No satisfactory account of the northern portions. of this field has 

 hitherto been published ; many coal-seams, of eight, six, and four 

 feet in thickness, are worked in it. The southern portion is of much 

 more importance, as it contains seams from 30 to 45 feet in thickness. 

 This enormous thickness is however not one continuous seam, but a 

 number of seams, divided by layers of what the miners call band, 

 which are very thin beds of clay-ylate. The working of these thick 

 .seams is not so profitable as might be supposed. The pillars left 

 standing in order to support the high roof are estimated at about one- 

 third of the whole coal in the bed, and the small coal left in the mine 

 is about equal to another third, so that only one-third of the whole is 

 at present taken out of the mine. 



In the coal-measures of this district there is an absence of the 

 millstone grit, carboniferous limestone, and old red-sandstone, which 

 usually lie under the coal-measures. The coal-measures rest, in the 

 Dudley Coal-Field, on the transition rock at once, without any inter- 

 mediate strata : this singularity is likewise observed in the Coal- 

 brook Dale coal formation. 



The coal district in South Staffordshire is traversed from north- 

 west to south-east by apparently a line of hills, but they are riot 

 absolutely continuous, though they have a uniform general direction. 

 On examination, the hills on the north and those on the south of 

 Dudley are found to differ entirely in their character. The northern 

 chain consists of highly inclined strata of limestone, against the 

 Rides of which all the coal-measures crop out at a considerable anple, 

 but come nearer a horizontal position as they recede from these 

 hilla. The other chain of hills, on the south of Dudley, is entirely 

 composed of one mass of basalt and amygdaloid, and the coal- 

 measures preserve their usual level in approaching the hills, not 

 cropping out as they do upon the limestone chain. Two opinions 

 are entertained with regard to these basalt elevations : " they may 

 be either the protruding edge of a vast basaltic dyke traversing the 

 coal-field, or an overlying mass :" the latter is considered the more 

 probable. The coal-measures on the south, near Stourbridge, appear 

 to dip beneath the beds of the newer red-sandstone formation : the 

 bed* of this and of the Warwickshire coal-field dipping in opposite 

 directions under the super-strata, give reason for suppos.ng that they 

 may extend continuously below this through the intervening space. 

 The eastern side of the field, which extends a little beyond Walsall, 

 is bounded by the same limestone with that of Dudley, and the coal- 

 measures are observed again to crop out against it, thus lying in a 

 basin between these two towns. That the coal-beds rise towards the 

 north, and the upper ones crop out while others continue under the 

 surface, is very satisfactorily shown by the comparison of the strata 

 in different collieries. At Tividale the main coal is 60J fathoms 

 below the surface ; at Bradley it is only 20^ ; and the greater number 

 of beds which cover the main coal at the former place have entirely 

 disappeared before the main seam reaches Bradley ; and farther to 

 the north the main seam also crops out and disappears altogether. 

 A very curious phenomenon takes place at Bloomfield colliery, to the 

 south of Bilston, thus described in the ' Geology of England,' p. 412 : 



-" The two upper beds of the main coal, called the roof, floor, and 

 top slipper, separate from the rest, and are distinguished by the 

 name of the ' flying reed.' This separation grows wider, and at 

 Bradley colliery amounts to 12 feet, four beds of shale (slate-clay) 

 and ironstone being interposed. These two upper beds crop out, 

 while the rest of the main coal goes on to Bilston, and is only eight 

 yards thick." 



This district supplies coals to the numerous iron-works in the 

 immediate neighbourhood, and the manufactories of Birmingham 

 and its vicinity ; besides which, all the neighbouring counties, as 

 far south as Reading and Gloucester, are supplied by means of inland 

 navigation. 



The clay ironstone occurs in various bedn, but is only wrought 

 in two : one of these is the bed under the main coal, and is wrought 

 for iron-ore. 



Many faults or dykes occur in this field ; they are usually fissures 

 in the beds, filled up with clay, and very frequently the levels of the 

 different strata vary in consequence. There is a great fault near 

 Bilston, which causes the dip of the strata to be reversed, the beds 

 on the south side dipping south, and those on the north side dipping 

 north : this is however an unusual circumstance. 



