On the Disturbances in the District of the Valley of The

Downloaded from http://pygs.lyellcollection.org/ by guest on September 28, 2021 mittee, for their kind assistance in making the arrangements for the meeting. The following communications were then made to the Society :— ON THE DISTURBANCES IN THE DISTRICT OP THE VALLEY OF THE DON. BY REV. WM. THORP, OF WOMERSLEY. Upon the last visit of the Society to Sheffield, I had the pleasure of describing some of the geological features of the neighbouring district, and particularly those of the country between Rotherham and Sheffield. I have again taken the liberty of giving a brief mining notice of the disturbances of the same district, because they are not only of such enor mous magnitude as to be of great interest to the geologist, but a knowledge of them is necessary to the successful min ing operations of that neighbourhood. Upon the former occasion, it was contended by one party that not only were the strata on the North side of the Don elevated above those of the South side, to the amount of 600 yards in vertical height; but that also there had been a horizontal lateral movement of the beds of the North side, in an eastward direction, to the length of five or six miles.^ * The proofs then adduced in support of a lateral movement were—1. That the various beds come from the North, up to the edge of the valley of the Don, but do not preserve their Northerly and Southerly direction across the valley, but are found several miles to the West; e. g.^the Silkstone coal ranges to Dropping Well, near Kimberworth, and is not found at the same depth until we arrive six miles West, at SheflSeld town. 2. A sudden variation in the direction of the water levels, from North and South to East and West, down the valley of the Don. 3. A fault, of exactly fifty yards, in the ironstone at Tankersley Park, running North and South; and another fault in the same ironstone, in Tinsley Park, [ten miles distant,) running in the same direction, and being i)f the same amount, were supposed to be one and the same fault, before the lateral traction Downloaded from http://pygs.lyellcollection.org/ by guest on September 28, 2021 I hope, however, now to be able to prove—1. That there is no vertical elevation of the beds of the whole country, on the North side of the valley of the Don, or, that the pre viously described elevation is merely local;—2. That the supposed lateral movement is due, in reality, to a depres sion or synclinal axis of the beds on the South side. It is, indeed, true that there is a vertical elevation, in the beds of the North side, over those of the South, if you com mence at Iccles Hall, and trace any of the deeper beds as far only as Keppel's Column ; but, in this case, part only of the disturbed country is described. These disturbances ex" tend over a much greater tract of country than is generally supposed : for instance, in the Thick coal they commence on the borders of Derbyshire, and extend as far as Elsecar; so that the whole country from Orgrave, near Beighton, and perhaps beyond it, to Elsecar, North of Wentworth House, is disturbed by variable and sudden inclinations of strata to the horizon, by one synclinal, and probably two anticlinal axes, and is more or less broken by faults of considerable magnitude ;—similarly, the disturbances commence in the Sheffield coal. North of Birley Moor, and terminate only at Chapel Town ; and in the Gannister, at Dore, three or four miles on the South side of Dronfield, and terminate only at Deep Car; but beyond the tw^o points where each of these beds first becomes regular, or assumes its usual inclination to the West, there is indeed no material elevation of one side of the country above the other. In order to prove this, it is only necessary to ascertain the diiference in elevation above the sea, or between each took place. The proofs in support of a vertical movement were, the abrupt rise of all the beds to the North, between Rotherham and Sheffield; accompanied with several faults, which elevate the beds to the North, both of which are seen in Mr. Chambers' Works, at the Holmes, and on the line of the Sheffield and Rotherham Railway, These are further explained in the sequel. Downloaded from http://pygs.lyellcollection.org/ by guest on September 28, 2021 6 other, of any of the same beds, at the two points where the disturbances cease, on a North and South magnetic line. I shall, therefore, take one of the uppermost beds in the series, and one of the lowest—i. e., the Thick coal at Orgrave, on the edge of Derbyshire, and the same bed at Elsecar ; and the Grannister, or Pecten coal, at Dore Moor, in Derbyshire, and the same at Deep Car. Now the fall of level on the surface, from Elsecar to Swinton, is 67 feet, or 22^ yards, and the fall from Orgreave, on the North Midland Railway, to Kilnhuret, is not more than forty yards, and probably less; so the difference in point of level can only amount to eighteen yards. Again, the Gannister or Pecten coal, at Dore Moor, from barometrical observations made by me, in 1838, is 48 yards above the river Sheaf, at Hunter's Lane Bar; and Deep Car, through which passes the Manchester and Sheffield Railway, with a gradient of five yards to the mile, being eight miles distant, will give forty yards of ele vation above Sheffield ; so that the difference of elevation between the same coal at Dore Moor and at Deep Car, will only amount to a few yards. Thus, there is no material difference, in level, of the Thick coal, which, in the scale of strata, is a higher bed ; and, similarly, in the lowest worked bed, the Gannister. There is, therefore, no material elevation in the country on the North, above the same beds on the South side of the valley of the Don ; the intervening disturbances, therefore, are merely local, and have no gene ral effect upon the stratification of the whole country. I now proceed to shew that the supposed lateral movement is due to a depression of the beds on the South side of the Don. The water levels* on each side of the disturbed dis- * A water level is a line at right angles to the steepest inclination of the coal, and is correctly represented by the spouts which carry water in any street; if the roofs of the houses rise due West, the direction of the street will be North and South, and the line of spouting, or water level, will be the same. A change of direction, therefore, in the water level, merely indicates an azimuthal change of the inclination of the coal-bed. Downloaded from http://pygs.lyellcollection.org/ by guest on September 28, 2021 trict run due North and South, by the compass ; but, in the distracted country, the beds rise more to the South, and the levels change to 23° and 28° to the West of North ; now, by this southerly rise, there is communicated to the dis turbed beds a dip of one yard in 20 or 25, in the due North and South direction^ ; so that, from Beighton to the turn or axis where the beds rise North, by the change of level alone, any single bed will be 150 yards deeper (supposing the sur face level.) This southerly rise is proved by the extensive water levels in the Sheffield coal, which, at Birley Moor, the most southerly point of the Sheffield Coal Company's workings, run due North and South, magnetic ; but, upon coming further North, the levels change to 23° West of North ; they are two miles in length, and, upon the colliery map, are semicircular. Again, the due North and South line from Orgreave runs over Brinsworth to Jordan Dam ; Brins- worth is equi-distant from the two places, and stands upon the red rock of Rotherham. Now it is most certain that the Thick coal at this place has sulFered an enormous depression, and that Brinsworth stands over the bottom of a synclinal trough ; for the Thick coal is here 350 yards deept, while at Orgrave pit it is 120 yards, the surface at Brinsworth being 18 yards higher. From Orgreave to Brinsworth, then, the Thick coal is depressed, either by dislocations or the va riation of level, or by both, to the amount of 200 yards at least. From Jordan Dam, a place near the Sheffield and Rotherham Railway, the same bed is depressed in an oppo- * These beds rise 1 yard in 7. At an angle of \5o, or half between the level and steepest iLclination, 1 in 14; at an angle of 30°, I in 21, which last is nearly the direction of the Tinsley Park and High Hazles Levels. In fact, the rapid rise of strata, of 1 in 7, would of itself lead to the supposition that the whole beds were irregular. t The four foot coal is 140 yards under the red rock of Kotherham, which is here 30 to 40 yards thick. The High Hazles Coal is 80 yards under the four- foot coal; and the thick coal 91 yards under the latter. Downloaded from http://pygs.lyellcollection.org/ by guest on September 28, 2021 8 site direction, south towards Brinsworth, but to a greater amount, for the Thick coal appears on the railway rising at a very acute angle to the North.

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