COALBROOKDALE.--This coalfield, which lies to the east of the Wrekin, covers an area of about 28 square miles. It originally contained about 28 coal seams, but the majority of these are now practically worked out. The succession includes the Carboniferous limestone, the Millstone grit, and the Lower coal-measures in conformable sequence. The Upper coal-measures rest in a hollow eroded out of the Lower coal-measures beneath, forming what is locally known as the “Symon Fault.”
The Permian rocks of the Birmingham District are totally distinct in their petrological characters from those of the typical area of Yorkshire and Durham. No true limestones are present, and the formation is wholly made up of red sandstones, marls and beds of angular breccia.
The lowest zones of the Permian repose conformably upon the Upper Coal Measures of the South Staffordshire Coalfield in the slopes of the hills to the south of Halesowen, and its strata are seen in corresponding relation to the Carboniferous on the east of the Coalfields of the Forest of Wyre and Coalbrookdale, and to the west of the Coalfield of Eastern Warwickshire.
The Permian is everywhere covered up unconformably, or locally overlapped, by the various members of the Triassic formation; all the subdivisions of the Triassic series being found resting immediately upon it in turns as they are followed from the valley of the Severn to the neighbourhood of Charnwood Forest.
In the neighbourhood of Enville and the Forest of Wyre, three divisions are recognisable in the Permian, viz.:--
(1.) _Lower Red Sandstones and Marls_, with bands of calcareous conglomerate.
Round the South Staffordshire Coalfield the Breccia is the highest division exposed, and this only occurs in force to the south of the coalfield.
Between Tamworth and Kenilworth, to the east of Birmingham, the Permian strata floor a wide tract of country, and lie almost horizontal. Red sandstones, marls and beds of breccia occur in association, but the divisions named above are not individually recognisable.
By far the most striking local member of the Permian formation is the so-called _Volcanic or Permian Breccia_. It is found in scattered patches over an area of about 500 square miles, extending from the Malverns to Enville, Stourbridge, and the Lickey Hills. It is made up of angular fragments of volcanic rocks, tuffs, altered shales, grits, and slabs of fossiliferous sandstone and limestones, all embedded in paste of bright red marl or pebbly sandstone. It is usually both underlain and overlain by red sandstones and marls, but sometimes, as at Stagbury and Woodbury Hills, &c., in the Valley of the Severn, it reposes at once upon pre-Permian rock.