COAL MEASURES. 20$ 



down in this area. Hence he truly observes that " Coal under 

 London" has really been found, though as yet, unfortunately, not 

 in situ} 



Ecojiomic products, etc., of Coal-measures. 



Supply and Duration of Coal. — The subject of our supply of coal has been 

 exhaustively treated in the Reports of the Royal Coal Commission.'* It appears 

 that there is a quantity of Coal in England and Wales in the visible Coal-fields, 

 available at a depth not exceeding 40CXJ feet, equal to upwards of 80,000,000,000 

 of tons ; whilst the amount of coal similarly available beneath the Permian and 

 newer strata, is estimated at about 56,000,000,000 of tons. The probable duration 

 of our supply is variously estimated, but it is considered good, at depths readily 

 accessible, for about 250 years. Mr. R. Meade has estimated the entire amount 

 of coal available from 1880 in the known Coal-fields of England and Wales at 

 69, 192,056,317 tons ; while reckoning the coal of Scotland and Ireland, and of the 

 concealed Coal-fields as well, he thinks that supplies are insured for 920 years 

 hence. ^ 



In illustration of the economic uses of coal, it may be mentioned that the pro- 

 ducts of the distillation of loo tons of Cannel Coal (according to Sir H. E. 

 Roscoe) would be as follows : — 



Gas 10,000 cubic feet, or 22 tons. 



Coke about 60 tons. 



Ammonia liquor 9^ ,, 



Tar 8| „ 



The ammonia liquor is sold for purposes of manufacturing ammoniacal salts 

 and alum. The coal tar yields carbolic acid, naphthaline, paraffin, and benzole ; 

 and from benzole are produced the beautiful aniline colours (mauve, magenta, etc.). 



Paraffin was formerly distilled from the Cannel Coal of Leeswood, south-east 

 of Mold. 



The flags and sandstones are extensively quarried for building- and paving- 

 purposes, for firestone and for grindstones ; while some of the beds (in Yorkshire) 

 are used for polishing marble and the copper-plates for engravers. 



The clays of the Coal-measures are used in the manufacture of bricks and tiles, 

 earthenware and pottery. The Fire-clays have been extensively manufactured 

 into fire-bricks at Stourbridge, and also at Newcastle, Bradford, and in South 

 Wales. These clays, known as ' Refractory Clays,' are so termed because they 

 resist exposure to high temperatures, without melting or becoming soft or pasty. 

 They contain but little iron, and are nearly free from lime and alkalies. The 

 Stourbridge clay consists of 79 percent, of silica, and 13 per cent, of alumina, 

 and contains but little water of combination, on which the plasticity of clay 

 depends.* 



In Shropshire a red marl from the Coal-measures has been employed in the 

 manufacture of encaustic tiles. 



Haematite occurs in nodules and bands in the Coal-measures of Cumberland, 

 also near Leek, and at the fire-clay workings at Swadlincote, near Burton-on-Trent. 



The Clay-ironstones (Sphaerosiderite) of the Coal-measures yield much of the 

 iron in this country, and they occur sometimes in thin seams, but usually in 

 nodules. They are composed mainly of carbonate of iron, with also carbonates of 



\ Q. J. xl. 760. 



■ See also W. S. Jevons, The Coal Question, 1865. 



■' The Coal and Iron Industries of the United Kingdom, 1882, p. 313. 



* J. Percy, Metallurgy, 1875. See also Catalogue of Specimens in the Museum 

 of Practical Geology of British Pottery, etc., 3rd edit., by T. Reeks and F. W. 

 Rudler. Appendix on clays, by G. Maw. 



