THK SOUTH STAFFORDSHIRE COAL-FIELD. 251 



tire extension of the workj they are about three feet square, and 

 various contrivances are adopted to promote the circulation of a 

 stream of pure air through the cavities of the mine, both for the 

 purpose of ventilation, and for the extrusion of the deleterious gases 

 and vapours, which so frequently, in spite of all precautions, cause 

 tremendous and destructive explosions. Another enemy of the 

 miner is the water which is generally found in mines. This is 

 carried by channels or passages, to a general reservoir, or " sump," 

 from whence it is raised to the surface by a steam-engine. 



The ironstone is found in beds of three to five feet thick ; some- 

 times in the form of continuous strata or ' flats,' but most frequently 

 as nodules of different sizes embedded in matrices, of coarse clay. 

 It is entirely cleared ; a plentiful supply of matter for supporting 

 the roof being found in the stony and earthy refuse. In the mines 

 both of coal and ironstone, the " gate-roads," or passages of access, 

 are driven, aljirst, to the extremity of the proposed area, and the 

 work then proceeds " homeward," thereby avoiding the difficulty 

 and danger attendant on keeping open and continually re-entering 

 the cleared parts. 



Another mineral substance, of less value, but still of considerable 

 importance, is the Fire Clay, which abounds in various situations, 

 but is procured of the best quality in the neighbourhood of Stour- 

 bridge. Its superiority consists in its almost entire freedom from 

 admixture with oxide of iron, and its consequent power of resisting 

 extreme heat. This property renders it highly useful for the lining 

 of smelting furnaces, and for crucibles and other vessels used in the 

 making of glass, and in melting of metals for the founder. The 

 mode of clearing out the clay is similar to that of the ironstone. 



The iron-ore is an aqueous combination, in which the metallic 

 particles are mixed with large quantities of argillaceous matter, and 

 the science of the chemist is appealed to, in order to discover a sub- 

 stance which, uniting itself with the clay, should set free the metal. 

 Such a substance, possessing the desired affinity, is the limestone, 

 which is accordingly thrown into the furnaces with the coal and 

 ironstone, when the metal runs off below, and the mixed matters 

 form a species of imperfect glass, which is suffered to escape by pas- 

 sages contrived for the purpose. 



The lecturer here introduced a detailed account of the operations 

 of the iron-furnace, the forge, and the mill, to which, however, we 

 can only thus allude. He then adverted to the remarkable features 

 presented, in certain situations, by the pyrogenous rock already 

 mentioned, which forms a line of hills commencing where the lime- 



VOL. VII., NO. XXII. KK 



