thick; and at a depth of 90 feet below that the Thick limestone, which is there 30 feet thick.
At Bentley, south of Pouk Hill, the top of the Silurian shale was about 160 feet deep, and the Thin limestone 373. In the Chillington colliery near Wolverhampton they reached Silurian shale at a depth of 580 feet, and passed through shale and thin bands of limestone for more than 200 feet additional.
In addition to the above places where the Silurian rocks have been reached through the Coal-measures, we have at Deepfields the top of the Silurian shale 680 feet, and the top of the limestone 850 feet deep; at Dudley Port Silurian shale at a depth of 550 feet, the limestone at 620 feet; at the pits at Langley Green, south of Oldbury, a considerable thickness of Silurian shale passed through in a pit net more than 390 feet deep; and the same rock but a little way below the Thick coal at West Bromwich Heath pits.
If we look at these facts, together with that of the protrusion of Silurian rocks at Turner's Hill, the Hayes near the Lye Waste, and the Lickey, we are led irresistibly to the conclusion that a great floor of Silurian rocks stretches immediately under the comparatively thin covering of Coal-measures throughout all the coal-field south of Bloxwich at all events.
The central portion of the coal-field.—The central portion of the coal-field lies in the hollow or basin between the Silurian ridge of the Dudley and Sedgley anticlinal and the Walsall elevation.
If we take Tipton old church, the Moat colliery, and Princes End and that neighbourhood as a centre, the beds, being there deepest, rise thence gently towards the surface in every direction except towards the south. As they approach closely to the Dudley and Sedgley anticlinal they are bent up much more rapidly than elsewhere, the angle of inclination near that outcrop being in some places nearly vertical, and generally as much as 20° or 30°.
The beds rise more gently on the east towards the Walsall Silurian ground, at a mean angle of about 5° perhaps, but still more gently on the north, where the space between the outcrop of the Thick coal and that of the New mine coal is not less than two miles, although the vertical thickness between the two beds does not exceed fifty-six yards (or 170 feet). This gives a mean inclination of only about 1 in 62, or less than 1°. In the same way the Thick coal, when it does take the ground, between Wolverhampton and Bilston, declines so gently into it as never to be more than forty yards deep, and consequently never to be deep enough to take in the Brooch[1] above it for more than a mile to the southward, till it meets the Lanesfield fault. South of that district the measures in all the middle part of the central portion scarcely vary from a horizontal position. Notwithstanding the nearly horizontal "lie" of the beds over the greater part of the central and south-eastern district, the depth of any measure, as the Thick coal for instance, varies frequently. This variation is produced to a slight extent by the undulations of the surface, but chiefly by the upthrow or downthrow of the faults.
In describing the south-western district it was shown that the two basins into which it is divided were connected at the northern end of the Netherton anticlinal by a trough, which we proposed to call, from
- ↑ It is probable that over this space, even if the Thick coal did exceed that depth, that the Brooch would not come in, as the Flying reed coal or upper part of the 'Thick would come between them.
