66 VESTIGES OF THE 



with sandstones, shales, beds of Hmestone, and ironstone. 

 Coal is altogether composed of the matter of a terrestrial 

 vegetation, transmuted by pressure. Some fresh-water 

 shells liave been found in it, but few of marine 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 pro- 

 ductions, 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 the 

 arrangement of coal beds. In France, they rest imme- 

 diately on the granite and other primary rocks, the 

 intermediate strata not having been found at those places. 

 In America, the kind called anthracite occurs among the 

 slate beds, and this species also abounds more in the 

 mountain limestone than with us. These last circum- 

 stances only show that different parts of the earth's sur- 

 face did not all witness 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, covered with a luxuriant vegetation. Next we 

 have a comparatively brief period of volcanic disturbance 

 (when the conglomerate was formed). Tlien the causes 

 favourable to the so abundnnt production of limestone, 

 and the large population of marine acrita, decline, and 



