COAL MEASURES. 1 89 



period. The coal beneath the basalt has been altered and has 

 lost its inflammability. 



A group of sandstones, known as the Halesowen Sandstones, 200 to 300 feet 

 thick, occurs in the Upper Coal-measures, above the red and mottled clays in the 

 southern portion of the Coal-field. 



The Coal-measures rest on an irregular surface of the Silurian 

 rocks, which rise to the surface at Dudley, Sedgley and Hay Head. 

 The lowest beds of the Coal-measures consist of sandstones, con- 

 taining pebbles of quartz and fragments of Silurian shale and 

 limestone. The junction was well shown in the railway-cutting at 

 Trindle Gate, east of Dudley.^ 



The Ironstone measures, which supply material for the iron- 

 foundries of Dudley and the factories of Birmingham, range beneath 

 the Thick coal from Wednesbury and Bilston, Walsall and Wolver- 

 hampton, to Cannock Chase. To the south they occupy the district 

 between Stourbridge and Halesowen, and yield the well-known 

 " fire-clays." ^ The term Blackband ores is applied to layers of 

 ironstone and clay, alternating with coaly matter. 



At Bilston, in Staftbrdshire, certain fine sandstones are quarried 

 for the Bilston grindstones, which are of great excellence. A 

 burning coal-seam has been noticed at Bradley, near Bilston.^ 



10. SEVERN VALLEY COAL-FIELDS. 



The Severn Valley Coal-fields include several straggling and 

 isolated tracts of Coal-measures in Shropshire and Worcestershire. 

 Among these are the Shrewsbury Coal-field, the Coalbrookdale 

 Coal-field, and the Forest of Wyre Coal-field. 



The Shrewsbury Coal-field includes a tract extending south- 

 westwards of that town, and a detached tract extending to Le 

 Botwood to the south. In the upper series of Coal-measures, 

 here and in the Forest of Wyre, there are two beds of limestone, 

 from three to seven feet in thickness, containing Spirorbis pusillus, 

 and known as the ' Spirorbis Limestone.'* 



In the Coalbrookdale Coal-field, which extends from near 

 Lilleshall, southwards between Wellington and Shififnal, and 

 includes the district around Broseley, INIadeley, and Iron-Bridge, 

 the Coal-measures are divided as follows:^ — 



Upper Series. — Mottled clays and greenish grits ; calcareous breccia with band 



of Spirorbis Limestone. 300 feet. 

 Middle Series. — Yellow sandstones, shales and clays, with ironstones, and 



coal-seams. Fish-remains, Anthraeosia. 

 Lo'iVer Series {Canister or Penny stone Series). — Sandstones, shales with coal 



and ironstone (Pennystone and Crawstone bands). Marine fossils. 



^ South Staffordshire Coal-field (Geol. Survey), edit. 2. 

 ^ Murchison, Proc. G. S. ii. 40S. 

 ^ G. Mag. 1S67, p. 47. 



* Daniel Jones, Trans. Manchester G. S. x. 37. 



* See E. Hull, Q.J. xxxiii. 629; also J. Prestwich, T. G. S. (2), v. 428. 



