Murchisoris Silurian System. 223 



" The irojistone so largely worked in this field is both concretionary 

 and flat-bedded, but for the most part in the former condition, and the 

 various courses of it are known under these names : New mine (peculiar to 

 Madeley) Crawstone, and Pennystone, occurring generally ; white and blue 

 flats, in the north and middle districts; Chanestone and yellowstone, 

 in the middle tract ; ballstone, briekstone, and blaekstone, in the northern 

 district. The Ragged Rabins and Channe Pennystone are of irregular 

 occurrence. Of these twelve courses of ironstone more than seven are 

 never found in one locality. In taking a general survey, it may be said, 

 that both the coal and iron are much more abundant in the northern 

 than in the southern part of the field. Mr. Prestwich has indeed 

 remarked the difficulty of identifying any particular stratum of the 

 upper portion over a considerable area, whilst he has found the lower 

 measures stronger and more persistent. Among the various rocks 

 which alternate with the coal and iron, the stone of the Willey or 

 Shirlot obelisk is an example of a coarse variety, while the sandstone 

 occurring immediately above the " flint-coal," is of remarkably fine 

 quality for architectural purposes, the monument erected to the late 

 Duke of Sutherland on Lilleshall hill being built of it. Some of the 

 grits associated with the lower coals pass into coarse conglomerates 

 containing fragments of quartz rock, trap, Silurian and Cambrian rocks ; 

 and in the lower measures some of the beds of shale afford excellent fire 

 clay, long celebrated in the manufacture of pipes and pottery. 



" The ores of iron are peroxides in the sandstone, argillaceous carbo- 

 nates in the shale, and sulphurets in the coal. The sulphuret of iron is 

 the most abundant mineral, and next to it the sulphuret of zinc or 

 blende, which appears in the ironstone nodules of the Pennystone 

 measures both in granular and crystalline form. Petroleum is of con- 

 stant occurrence in the upper as well as lower measures ; the chief 

 source of this mineral at Coalport, which formerly afforded one hogs- 

 head per diem, being in a thick bedded sandstone of the upper measures. 

 This supply has, however, much decreased with the opening of the new 

 coal works. Other tar wells have been discovered in the lower coals at 

 Prior's Lee. In some pits, as at Dawley and the Dingle, the petroleum 

 exudes in such quantities that the works are necessarily boarded up or 

 " plated" to prevent its infiltration upon the workmen. Besides these 

 minerals titanium exists in the iron ore." 



Of the fossils of Coalbrook dale coal field, Mr. Murchi- 

 son remarks that upwards of 50 species of plants have al- 

 ready been discovered, consisting of Euphorbiacece, Dyco- 

 tyledons of doubtful characters, Palmce, Monocotyledons of 



