MANUAL OF NATURAL HISTORY. 553 



III. — Carboniferous Group. 



This most extensive series is composed of shales, 

 sandstones, ironstones, clays, millstone-grit, and 

 limestone, in alternating strata of marine and 

 fresh-water formation, interstratified with seams of 

 coal. 



The Coal-measures are formed of alternating beds 

 of coal, shale, sandstone, and clay, with seams of no- 

 dulous ironstone. The coal itself consists of ancient 

 plants, altered by chemical agency, and imbedded 

 in sand and mud. Sometimes the plants grew where 

 the coal now exists, or they were washed down into 

 estuaries, forming vast accumulations. The coal- 

 fields of the British islands are very numerous, and 

 are found in South Wales, England, Ireland, and 

 Scotland ; the gross value of the collieries being 

 upwards of nine millions sterling. Three millions 

 five hundred thousand chaldrons are annually 

 brought into London, in nearly ten thousand ships. 

 There are also coal formations in New Holland, in 

 the East Indies, in China and Japan, in Borneo and 

 Labuan ; also in our colonies of Newfoundland, New 

 Brunswick, Nova Scotia, Cape Breton, Prince Ed- 

 ward's Island, New Zealand, and Port Natal. The 

 position of the beds is often very different, many of 

 the seams of Newcastle being worked under the sea, 

 while at Chipo, which rises above the plain of Santa 

 Fe de Bogota, coal is found 800 feet above the sea, 

 and at Buanco, at 12,800 feet, or bordering on the 

 limits of eternal snow. 



