w.] THE COAL IN THE PIEE. 99 



is pierced everywhere by the roots of the moss forming 

 the peat, or of the trees,, birches, alders, poplars, and 

 willows, which grow in the bog. So the proof seemed 

 complete, that the coal had been formed out of vege- 

 tation growing where it was buried. If any further 

 proof for that theory was needed, it would be found 

 in this fact, most ingeniously suggested by Mr. Boyd 

 Dawkins. The resinous spores, or seeds of the Lepi- 

 dodendra make up 'as said above a great part of the 

 bituminous coal. Now those spores are so light, that 

 if the coal had been laid down by water, they would 

 have floated on it, and have been carried away ; and 

 therefore the bituminous coal must have been formed, 

 not under water, but on dry land. 



I have dwelt at length on these further arguments, 

 because they seem to me as pretty a specimen as I can 

 give my readers of that regular and gradual induction, 

 that common-sense regulated, by which geological 

 theories are worked out. 



But how does this theory explain the perfect 

 purity of the coal ? I think Sir C. Lyell answers 

 that question fully in p. 383 of his " Student's 

 Elements of Geology." He tells us that the dense 

 growths of reeds and herbage which encompass the 

 margins of forest-covered swamps in the valley and 

 delta of the Mississippi, in passing through them, are 

 filtered and made to clear themselves entirely before 

 they reach the areas in which vegetable matter may 

 accumulate for centuries, forming coal if the climate 

 be favourable ; and that in the cypress-swamps of that 

 region no sediment mingles with the vegetable matter 

 accumulated from the decay of trees and semi-aquatic 

 plants ; so that when, in a very dry season, the swamp 



H 2 



