(f.) Bottom Coal, five feet and above.
These measures include several zones of workable ironstone, of which the most important are:—
(1.) The Pins and Pennyearth ironstones, below the Brooch coal.
(2.) The Whittery and Gubbin ironstones, below the Thick coal.
(3.) The Blue Flats, Silver Threads and Diamond Ironstones, below the Bottom coal.
For its size the South Staffordshire coalfield has proved itself the richest mineral area in Britain. Thick coal seams, rich bands of ironstone, and great thicknesses of Silurian limestone, all occur within a short distance of each other, and all within easy reach of the miner. The natural result has been that the South Staffordshire coalfield and its immediate neighbourhood has been the great coal and iron mart of Central Britain, and the abundance and cheapness of its material it has afforded, have rendered Birmingham and the “Black Country” the hardware workshop of the world.
Almost all the available coal seams and ironstone beds within easy reach have been long since practically worked out, but there is still much excellent coal and iron to be obtained at greater depths, especially in the northern part of the coalfield. Of late years the Triassic rocks which surround the coalfield have been pierced in order to reach the Coal measures beneath. An entirely new coalfield has been developed in this manner in the district of Cannock Chase; and two most remarkable collieries, those of Sandwell Park, and Hamstead, have been opened in the neighbourhood of Birmingham itself.
The area immediately underlain by the Coal measures constitutes the district of the “Black Country,” which extends from the western margin of Birmingham to the fringe of Cannock Chase. It includes within its limits, the large towns of Dudley, Walsall, Wolverhampton, Bilston, and others of scarcely less note.
The most remarkable seam of the South Staffordshire coalfield is that known as the Ten yard or Thick coal, a continuous bed of workable coal from 25 to 30 feet in thickness. This underlies all the south central part of the field in the area enclosed by Smethwick, Oldbury, Dudley, Walsall and Bilston. To the southward near Halesowen it thins out and becomes mixed with shaly material. It is in reality composed of 13 or 14 superimposed coal seams, which form an apparently unbroken mass, but are easily distinguished individually by the practised Thick coal miner. As we pass northward from the typical Thick coal area towards Walsall and Cannock Chase, the component seams become separated by intercalated sandstones and shales, so that eventually in the district of Essington and Pelsall the Thick coal is represented by 14 distinct coals occurring at intervals in a mass of sandy rock, between 500 and 600 feet in total thickness. The Thick coal is known to extend far to the eastward, beyond the present margin of the South Staffordshire coalfield. The first attempt to reach it through the red ground (Permian) was made under the bold and skilful guidance of the late Mr. Henry Johnson, C.E., of Dudley, at the locality of Sandwell Park. The coal was reached in 1873 at a depth of 1,250 feet and found to be of its original thickness, and of excellent quality. The next attempt which was made at Hamstead Hall, about three miles outside the limit of the coalfield, was even bolder and more hazardous, but it was eventually crowned with equal success; the Thick coal being reached at a depth of 1,800 feet. As the demand for coal increases, other collieries will doubtless be started at fresh localities outside the limits of the coalfield, for there can be no question that the Thick coal extends far to the eastward, under and beyond the town of Birmingham itself.
The strata of the South Staffordshire Coalfield afford the usual fossils of the British Coal Measures. The roofs of the coal seams, and the layers of carbonaceous shale, locally furnish well preserved examples of Lepidodendron, Sigillaria, Calamites, Annularia, Pecopteris, Neuropteris, etc., often associated with abundant specimens of the peculiar Unio-like shell, Anthracosia: while the ironstone nodules occasionally yield fragmentary Crustaceans and Insects. Marine fossils are principally confined to the lower beds of the series, below the Thick coal. Owing to the absence of true limestone beds in the coalfield, the characteristic corals, &c., of the Carboniferous are absent, but the following marine forms are not uncommon in the lower ironstones:—