COMMENCEMENT OF LAND PLANTS. 43 



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 

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

 diately on the granite and other primary rocks, the interme- 

 diate strata not having been found at those places. In other 

 countries, traces of coal are found in the Devonian formation. 

 These last circumstances may only show that different parts 

 of the earth's surface did not all witness the same events of a 

 certain fixed series exactly at the same time. 



Some features of the condition of the earth during the de- 

 position of the carboniferous group, are made out with a clear- 

 ness 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. Xext 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 

 radiata, decline, and we find the masses of dry land increase 

 in number and extent, and begin to bear an amount of forest 

 vegetation, far exceeding that of the most sheltered tropical 

 spots of the present surface. The climate, even in the lati- 

 tude of Baffin's Bay, was torrid ; and the atmosphere has been 

 supposed by some to have contained a larger charge of car- 

 bonic acid gas (the material of vegetation) than it now does. 

 The forests or thickets of the period included no plants speci- 

 fically the same with those now known upon earth. They 

 mainly consisted of gigantic vegetables, many of which are 

 not represented by any existing types, while others are akin 

 to kinds which, in temperate climes at least, are now only 

 found in small and lowly forms. That these forests grew 

 upon a Polynesia, or multitude of small islands, is considered 



