LIMESTONE 



COAL SEAMS 



THE CAEBONI 



The Carboniferous is the most important group connected with the industrial resources 

 of this and other countries. Independently of its supplying the valuable fuel coat, thli 

 series of strata contains other useful substances It is in this country the chief source o 

 the iron ores; it also yields fire-clay, millstones, marbles, and limestones, the lattei 

 enclosing rich deposits of lead ore. The group is commonly divided into Mountain Lime 

 stone, Millstone Grit, and Coal Measures, but these are subject to local variation. 



The Carboniferous or Mountain Limestone, may generally be regarded as the base of th( 

 whole Carboniferous group. In the north of England and Scotland, however, this limestone 

 is not a uniform bed underlying the coal measures. In Ireland and other parts of Europe 

 the limestone is separated from the Devonian Rocks by shales and sandstones. The thick- 

 ness of the limestone of this period varies from a few feet to 2,000 feet; the rock is usually 

 hard, and contains in its fissures numerous crystalline minerals, and ores of lead, zinc, anc 

 other metals. 



Above the carboniferous limestone a deposit of hard coarse sandstone supervenes, called 

 Millstone Grit; it often contains bands or seams of coal, but of small value. 



The series of strata which constitute the Coal Measures, consists of first, the under-da^ 

 or floor, a rough argillaceous substance, containing stems of stigmaria; secondly, the coat 

 which occurs in seams of from a few inches to six feet, and sometimes, though rarely, thirty 

 feet in thickness; thirdly, the roof or upper bed, generally consisting of slaty clay, often 

 containing layers of ironstone nodules. Interstratified with the shales, finely laminated 

 clay, micaceous sand, grit, and pebbles of other rocks, sometimes occur. The coal measures 

 are found in a greater or lesser extent in most European countries, also in Asia, Australia, 

 the United States, and other parts of America. 



From its bituminous' nature and structure, coal is presumed to be of vegetable origin, 

 and to have been derivecfTrom numerous plants which grew on the spot where the coal 

 seams are now found, or they were drifted into ancient estuaries arid covered by sand and 

 mud. These changes must have been successively repeated over large areas, as indicated 

 by the number of beds of coal which occur one above the other, as well as their great 

 extent. The plants found in the coal measures are chiefly ferns and other cryptogams, 



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