The Russells Hall fault.—On the south-west side of this indented outcrop[1] of coal runs the long Russell's Hall fault, which here throws down the Thick coal and other measures 120 feet to the south-west. Owing to a local flexure and rise of the beds, however, the Thick coal again crops out round Gornal Wood on the downthrow side of the fault.
The Russell's Hall fault running on the south-south-west side of the Sedgley and Dudley ridge, is continued to the south-east along the south-west flank of the Rowley Hills. It holds its course very regularly towards the south-east, its "throw" increasing as we proceed to the southward, up to 150, 180, and 240 feet, and eventually, near Rowley Regis, it has a downthrow to the westward of upwards of 400 feet. Beyond this its details are not accurately known, but at Coombs Wood it was partly proved by Mr. W. Mathews, and it seemed as if the fault were there passing into a very sharp anticlinal curve, a3 he found some Thick coal on the west side of it only 16 yards from the surface, and dipping at a high angle to the west, in which direction it acquires a depth of 750 feet in the space of a mile. On the east of the fault line it is known also to be 570 feet deep at a similar distance.
Near the foot of Mucklow Hill, a disturbance, probably due to this fault, may be seen in the Coal-measure sandstones, which dip 3° to the east on one side of it, and 30° or 40° to the south-west on the other. As the beds seem nearly, if not quite similar, it is probable that here also it is rather a rude anticlinal than a clean-cut fracture or fault.
The Rowley Basalt.—It is remarkable, that where the Sedgley and Dudley anticlinal ends, the mass of the erupted basalt of Rowley begins, and that hereabouts the Russell's Hall fault has its greatest amount of " throw," and is most of an actual fracture, while a mile south of the Rowley basalt the dislocation appears to be on the point of passing again into an anticlinal ridge. This almost looks as if there would have been a continuous anticlinal elevation all the way from Sedgley to the south end of the Lickey had it not been for the eruption of the Rowley rag. If the eruption of the Rowley basalt could be shown to have been subsequent to the formation of the whole Coal-measures, and contemporary with the fractures and dislocations of the coal-field, it might readily be accepted as a vera causa for the gap between the two anticlinals mentioned above. We should then suppose that the strain acting on the beds was relieved at one point by the actual outburst of trap, while in others it resulted in the uplifting and protrusion of the inferior rocks.
I believe, however, that this apparent connexion between the occurrence of the Rowley basalt and the dislocations and lie of the Coal-measures is an apparent and accidental one only. The change from a bold anticlinal to a mere depression, with a fault on one side of it. I think is due to the fact of the Dudley Port Trough faults cutting across the course of the anticlinal. These faults actually dislocate the Rowley basalt, which must, therefore, have been solid at the time of their formation.
- ↑ Mr. J. Kenyon Blackwell was kind enough to accompany me in tracing the crop of the Thick coal hereabouts, with his ground bailiff, Mr. Waterfield. The outcrop of the coal was perfectly well marked by the occurrence, at the surface of the ground of fragments of "shattery." This is the local name for a well-known indurated shale, streaked red and green, and baked almost into jasper. After extracting the coal, the fragments of coal and shale are piled up in the hollows to afford a partial support to the roof. This mass of fragments is called the "gob," and ia shallow excavations, where the air and water from the surface find ready access, it frequently takes fire, and burns for a very considerable time with a slow combustion. Just at the west entrance of the town of Dudley, in a cutting of the road, smoke and steam may often be seen in damp weather rising through the joints and cracks of a sandstone rock, from the combustion of the "Thick-coal gob" below.
