46 CARBONIGENOUS ERA. 



beds of coal. It commences with the beds of the mountain 

 limestone, which, in some situations, as in Derbyshire and 

 Ireland, are of great thickness, being alternated with chert, 

 (a siliceous sandstone,) sandstones, shales, and beds of coal, 

 generally of the harder and less bituminous kind, (anthracite,} 

 the whole being covered in some places by the millstone grit, 

 a siliceous conglomerate, composed of the detritus of the ear- 

 liest formation. The mountain limestone, attaining in Eng- 

 land to a depth of eight hundred yards, greatly exceeds in 

 volume any of the primary limestone beds, and shows an 

 enormous addition of power to the causes connected with 

 animal life, by which this substance is supposed to have been 

 produced. In fact, distinct remains of corals, crinoidea, and 

 shells, are so abundant in it, as to compose three-fourths of the 

 mass in some parts. 



Above the mountain limestone commence the more con- 

 spicuous Coal Beds, alternating with sandstones, shales, beds 

 of limestone, and ironstone. Coal is altogether composed of 

 the matter of a terrestrial vegetation, transmuted by putrefac- 

 tion of a peculiar kind, beneath the surface of water and in 

 the absence of air. Some estuary shells have been found in 

 it, but few of pelagic origin, and no remains of those zoophytes 

 and crinoidea so abundant in the mountain limestone and 

 other rocks. Coal beds exist in Europe, Asia, and America, 

 and have hitherto been esteemed as the most valuable of 

 mineral productions, from the important services which the 

 substance renders in manufactures and in domestic economy. 

 It is to be remarked, that there are some local variations in 

 their arrangement. In France, they rest immediately on the 

 granite and other primary rocks, the intermediate strata not 

 having been found at those places. In other countries, coal 

 beds are found in the Devonian formation, and even lower. 



Some features of the condition of the earth during the 

 deposition of the carboniferous group, are explained with a 

 clearness which must satisfy most minds. First, we are told 

 of a time when carbonate of lime was formed in vast abundance 

 along the shores and islands of the ocean, accompanied by an 

 unusually large population of corals and encrinites ; while in 

 some parts of the earth there were pieces of dry land covered 

 with a luxuriant vegetation. Next, we have a comparatively 

 brief period of volcanic disturbance (when the conglomerate was 

 formed). Then the causes favourable to the so abundant 

 production of limestone, and the large population of marine 



