64 



A YEAR IX .SCIENCE 



of vegetation under swamp and marsh conditions. As 

 this fell and accumulated year after year, and century 

 after century, and became submerged, many of the 

 more volatile gases were driven off, with some of the 

 carbon, no doubt, but much of the carbon was pre- 

 served. As the pressure of the accumulating Aveight 

 increased, further changes took place until eventually 

 coal, our chief source of heating fuel, was produced. 



Copyright by Underwood tC- Undenvood, N. Y. 



Fig. 28. Cutting peat in Ireland, where it is used as a substitute 



for coal. 



Successive stages in coal formation are wood, peat, 

 lignite or brown coal, soft or bituminous coal, and hard 

 or anthracite coal. 



Coke is produced from coal in very much the same 

 manner that charcoal is produced from Avood. When 



