i So 



CHAPTER XII. 



VEGETABLE REFUSE. 



Petrified Wood Rapid Decay of Vegetable Matter in the Tropics Forma- 

 tion of Peat Dismal Swamp How Coal was Formed : Jungles, 

 Luxuriant Vegetation, Drift-wood The Club Moss, its Sacs and 

 Spores " White Coal," Brown Coal The Pitch Lake; Bituminous 

 Shales, Rock-oil Diamonds, " Black-lead," Amber, Iron Pyrites. 



VARIOUS are the fates of the vegetable scavengers, 

 when, their time of active service in that capacity 

 being over, they themselves fall under the head of " refuse," 

 and pass into the lumber room to be remodelled. 



Both at the Cape and in Australia, bushes near the shore 

 are often killed by the calcareous sand which buries them. 

 As they decay, some of their carbon is converted into 

 carbonic acid, which dissolves the lime immediately around 

 them, and as evaporation proceeds, this is re-deposited and 

 forms a solid crust round the bark. When the decay is 

 complete, and all the wood converted into gases and ash, 

 only a pipe of limestone remains, surrounded by loose sand ; 

 and often these pipes are filled with hard calcareous matter, 

 which makes them so solid that when the sand shifts and 

 they are left exposed they look, especially when branched, 

 like the white, stony skeletons of the shrubs they represent. 



Sometimes vegetable substances are petrified, that is, as 

 they decay and the various atoms of which they are com- 

 posed are set free and returned to the air, the place of each 



