HOW THE COAL BEDS 



Figuier, the advantage of size and rapid growth; but 

 how poor it was in species how uniform in appearance ! 

 No flowers yet adorned the foliage or varied the tints of 

 the forests. Eternal verdure clothed the branches of the 

 Ferns, the Lycopods (club mosses), and Equiseta, which 

 composed to a great extent the vegetation of the age. 

 The forests presented an innumerable collection of indi- 

 viduals, but very few species, and all belonging to the 

 lower types of vegetation. No fruit appeared fit for 

 nourishment ; none would seem to have been on the 

 branches. Suffice it to say that few land animals seem 

 to have existed yet ; while the vegetable kingdom occupied 

 the land, which at a later period was more thickly 

 inhabited by air-breathing animals. A few winged insects 

 gave animation to the air while exhibiting their varie- 

 gated colours; and many mollusca (such as land-snails) 

 lived at the same time. 



Ultimately all this richness of vegetation became by 

 decay, by compression, by submergence, perhaps by being 

 buried under earthquake movements and volcanic out- 

 breaks, converted into coal; and we may now ask how 

 long did this process take. A vigorous growth of vegeta- 

 tion has been estimated to yield annually about one ton 

 of dried vegetable matter per acre, or 640 tons to the 

 square mile. If this annual growth of vegetable matter 

 were all preserved for 1000 years, and compressed till it 

 was as dense and heavy as coal, it would form a layer 

 about seven inches thick. But a large portion of the 

 vegetable matter even in peat bogs escapes as gas in the 

 making of coal. Four-fifths of it escapes in this way- 



320 



