On the extension of the coal-fields of England under the more recent Permian and Triassic Formations
Authors: Hull Edward 
Published: December 2013

The existing coal-fields of Great Britain are being rapidly exhausted—the rate of production of coal having reached to the amount of more than 100,000,000 tons per annum, with the prospect of an increase corresponding to the increase of population, for which the estimate of Mr R. Hunt of one ton per head per annum might be adopted. In consequence of this rapid production, the mines of England are yearly tending to increase in depth, and to advance towards the margins of the formations which overlie the Coal-measures. Pits of depths from 500, 600, and 700 yards are not uncommon in the north of England, and one is now being sunk to a depth of 1000 yards at Wigan. Along the margins of the coal-fields of Durham, Yorkshire, and Derbyshire, Lancashire, Leicestershire, Warwickshire, South Staffordshire, and Shropshire, the Permian and Triassic rocks are now everywhere pierced by shafts to the coal below, while in the neighbourhood of Bristol this has long been the case. Under the circumstances, it becomes important to bring all the knowledge and experience which men of science possess to the determination of the question regarding the extent and limits of the coal-fields when they dip under, and lie concealed beneath, the more recent strata; and I consider that the time has come when geologists are in a position to deal with the subject in a satisfactory manner, particularly as the boundaries of the coal-fields and the relations of the superjacent rocks to those of the coal-period had been accurately determined by the Government geological surveyors. The extent of the coal-formation as originally deposited over England and Wales, shows that in the direction of Shropshire and to the south of the Dudley coal-field, as pointed out by Mr J. B. Jukes, there existed a tract of Palæozoic rocks which were never submerged during the coal period; and as a similar tract existed in Leicestershire, it was supposed that a barrier of land surface originally stretched across the centre of England from Shropshire, over which coal had not been formed. This barrier included the eastern counties; but to the south of it there was formed a large tract of coal-measures, originally including the coal-basins of the forest of Dean, Somersetshire, and South Wales, all originally united, and which possibly extended along the Thames valley into Belgium. To the north of the barrier there originally existed a great sheet of coal-measures as far, at least, as the southern uplands of Scotland, and which included the coal-fields of Warwickshire, Leicestershire, Staffordshire, Shropshire, Flintshire, and Denbighshire, Lancashire, and Cheshire, North Derbyshire, and Yorkshire, Durham, Northumberland, and Cumberland; the whole of these were originally united in one large, continuous sheet, which has only been parcelled out into disconnected coal-fields by subsequent disturbances of the strata, accompanied by denudation at several subsequent periods. At the close of the Carboniferous period, great disturbances, accompanied by denudation, occurred over the whole of the north of England, principally along E.N.E. and W.S.W. lines; and the coal-fields of Durham and Cumberland were dissevered from those of Lancashire, Cheshire, and Yorkshire. Another disseverance, owing to the uprising of the lower Carboniferous rocks, took place along the present southern margin of the Derbyshire limestone, and was continued, in the author’s opinion, under the central plain of Cheshire, westward into Flintshire. The enormous denudation of Carboniferous strata which occurred at this period might be illustrated by the fact that in the district of Clitheroe, where the Permian beds rest on the mountain limestone, no less than 13,000 or 14,000 feet vertical of strata had been swept away. As Professor Sedgwick remarked forty-three years ago, when referring to the period between the close of the Carboniferous and the commencement of the Permian, we can assign no definite limit to it—we may regard it, in fact, as a ‶missing link″ in the geological chain. Over the Carboniferous rocks thus disturbed and denuded, the Permian beds were distributed, lying, sometimes as in the case of the tract of Yorkshire north of Leeds, on the millstone grit series; in other places, as in the neighbourhood of Manchester, on the Upper Coal-measures. In the central counties, also, these beds rest generally on the Upper Coal-Measures, but sometimes on strata below the principal coal-seams; and, in speculating on the extension of the coal-fields under this formation, this is an element of uncertainty. The Permian beds in parts of Warwick and Shropshire attain a thickness of nearly 2000 feet, but thin out northward in Leicestershire along the barrier of Lower Carboniferous rocks, which seems to have dissevered the Permian beds of the north of England from those of the midland counties. At the close of the Permian period fresh disturbances, accompanied by denudation of all the Palæozoic formations, took place in the north of England along north and south lines. It was at this period that the Pennine chain of hills (or ‶backbone of England″) was upheaved, and the result was the ultimate separation of the Yorkshire and Derbyshire coal-field from that of Cheshire and Lancashire, owing to the sweeping away of the Coal-Measures over the intervening tract of upraised land. The intersection of the two great lines of elevation and disturbance at the close of the Carboniferous and Permian periods, together with the denudation of the upraised portions, was shown to have thrown the coal-fields into separate tracts or ‶basins,″ of which the existing coal-fields (as in the cases of South Lancashire and of Yorkshire) may be considered as segments, the other segments being hidden by the newer formations; and on these grounds we may consider the Durham and Yorkshire coal-fields to be limited eastwards by the uprising of the lowest beds beneath the Liassic and Oolitic formations. At the close of the Palæozoic period, subsidence of the whole area took place, and the submerged strata were overspread by the sandy and muddy sediment of the Trias, which was distributed in such a manner that it thins away towards the south-east of England, and terminates probably against the concealed barrier of old Palæozoic rocks, which has already been described as forming the limit of the Coal-Measures in the same direction. (See Ideal Section.) The thickness of the Triassic series in all parts of England has now been accurately determined by the geological surveyors, so that in questions of the depth of the Coal-Measures where the New Red strata occur this element of uncertainty no longer exists. For these reasons, I concur in the view expressed by Sir Roderick Murchison, at the meeting of the British Association at Nottingham, that coal would not be found under the eastern counties, or east of the Malvern and Abberley Hills. Along the valley of the Thames under the Chalk, Mr Godwin-Austin had shown that there were grounds for believing that Carboniferous strata exist along an axis or trough ranging east and west. On this point, while admitting the probability of Palæozoic rocks under this tract, I have reason to apprehend that they will prove to be of older date than the coal, but would be very glad to see the question set at rest by actual experiment. As the question of the extension of our coal-fields is now occupying the attention of a Royal Commission, which is engaged in collecting all the evidence that could be brought to bear towards its solution, I fully expect that results of great economic importance will arise from its labours.