THE WONDERS OF VEGETATION. 283 

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Coal was formed, as we know, by the prodigious 

 exuberance of primitive vegetation that covered 

 the whole earth. Every one has observed that in 

 damp cellars, in which dry wood is kept during win- 

 ter, there is a soft wood layer left behind, which re- 

 sembles vegetable mould ; and it is also well known 

 how our marsh-plants are gradually converted into 

 peat. In a similar but infinitely more powerful man- 

 ner was our early vegetation converted into coal. 



At the time that the vegetable world was pre- 

 paring for man the fuel necessary for his industry, it 

 appears to have been called on to play an important 

 part in the economy of nature that of purifying 

 for the good of the aerial creatures who afterwards 

 came to exist) the atmosphere which was surcharged 

 with carbonic acid gas. For though this gas is 

 of great importance to the growth of vegetables, it 

 is an obstacle to the existence of animals, and espe- 

 cially to the more perfect classes of animals, such 

 as mammals and birds. But when that ancient and 

 abundant vegetation fell and was closed over by the 

 earth, the carbon was no longer mingled with the air, 

 which gradually became purer and better suited to 

 the existence of animal life. 



THE END. 



