Rocks of Carboniferous age make their appearance at four distinct localities within the limits of the Birmingham District, viz., in the coal fields of Coalbrookdale, the Forest of Wyre, South Staffordshire, and East Warwickshire. The strata exposed on the last three of these coalfields are those of the upper Carboniferous or Coal measures; neither the Carboniferous limestone nor the Millstone grit being met with outside the limits of the coalfield of Coalbrookdale. In the Forest of Wyre the Coal measures rest upon the Old Red Sandstone, in the South Staffordshire Coalfield upon the various members of the Silurian, and in the East Warwickshire upon the Upper Cambrian rocks. In these three coalfields a two-fold division of the Carboniferous is recognisable:-- (_a._) _The Lower Coal Measures_ proper, consisting of grey sandstones and shales with occasional coal seams, some of which are of remarkable thickness. (_b._) _Upper Coal Measures_, or Halesowen grey and red sandstones, brick clays and marls, with occasional coal-seams, none, however, of commercial value. In the South Staffordshire and East Warwickshire coalfields, the well known “_Spirorbis Limestone_” of the Upper Coal Measures occurs in its normal place near the summit of the Carboniferous series. SOUTH STAFFORDSHIRE COALFIELD.--The Carboniferous rocks of South Staffordshire are arranged in a broad dome about 23 miles in length by 6 in breadth. Their basement beds rest unconformably upon the Silurian around the flanks of the Dudley Hills, and in the neighbourhood of Walsall. Their highest beds dip conformably below the Permian rocks at the southern extremity of the coalfield south of Halesowen, and are overlapped unconformably by the Triassic pebble beds at its northern extremity, in the district of Cannock Chase. The eastern and western boundaries of the coalfield are formed by lines of fault, which have flung down against the Coal Measures the various members of the Permian and the Triassic. The total thickness of the Carboniferous beds is about 1,300 feet, and the normal succession in the central and highest part of the coalfield is as follows:-- _Upper Coal Measures._-- _2a._ Halesowen Sandstone Group, 600 to 800 feet. _2b._ Red Coal Measure Clays. _Lower Coal Measures_, 500 to 600 feet, containing several excellent coal seams, of which the following are the most important:-- (_a._) Brooch Coal, 4 feet. (_b._) Thick Coal, 30 feet. (_c._) Heathen Coal, 3 feet. (_d._) New Mine Coal, 2 to 11 feet. (_e._) Fire Clay Coal, 1 to 14 feet. (_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.