COMMENCEMENT OF LAND PLANTS. 



43 



which, m some situations, as in Derbyshire and Ireland, 

 are of great thickness, being alternated with chert, (a si- 

 liceous sandstone,) sandstones, shales, and beds of coal, 

 generally of the harder and less bituminous kind, {anthra- 

 cite,) the whole being covered in some places by the mill- 

 stone grit, a siliceous conglomerate composed of the de- 

 tritus of the primary rocks. The mountain limestone, 

 attaining in England 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 

 cause formerly suggested as having produced this sub- 

 stance. In fact, 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 com- 

 mence the more conspicuous coal beds, alternating with 

 sandstones, shales, beds of limestone, and ironstone. Coal 

 is altogether composed of the matter of a terrestrial vege- 

 tation, transmuted by pressure. Some fresh- water shells 

 have been found in it, but few of marine origin, and nc 

 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 es- 

 teemed 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 remark- 

 ed, that there are some local variations in the arrange- 

 ment of coal beds. In France, they rest immediately on 

 the granite and other primary rocks, the intermediate 

 strata not having been found at those places. In Ameri- 

 ca, the kind called anthracite occurs among the slate-beds, 

 and this species also abounds more in the mountain lime- 

 stone than with us. These last circumstances only show 

 that different parts of the earth's surface did not all wit- 

 ness the same events of a certain fixed series exactly at 

 the same time. There had been an exhibition of dry land 

 about the site of America, a little earlier than in Europe 

 Some features of the condition of the earth during the 

 deposition of the carboniferous group, are made out with a 

 clearness which must satisfy most minds. First, we are 

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

 abundance at the bottoms of profound seas, accompanied by 

 an unusually large population of corals and encrinites ; 

 while in some parts of the earth there were patches of 

 dry land A covered with a luxuriant vegetation. Next, we 



