570 GEOLOGY 



table 1 suggests certain changes which might take place, and also the 

 products which would remain at certain stages of the process: 



Wood 2 (timber) .... C 36 H 54 24 =6(C a H,0 4 ) 



r 8C0 2 i 



Subtract \ 4CH 4 }■ = C 12 H 28 22 



L 6H 2 J 

 And there remains C 24 H 26 2 = about the composition of brown coal. 



Wood C 36 H 64 24 



f 6C0 2 ] 

 Subtract^ 4CH 4 \ =C 10 H 3C O 22 



1 10H 2 O J 

 And there remains C 2G H 18 2 , which falls within the range of bituminous coal. 



6C0 2 1 

 Subtract <j 6CH 4 [ = C 10 H 4G 23 



[11H 2 0J 

 And there remains C 24 H 8 0, which falls within the range of anthracite. 



Since the changes above are changes which take place in peat- 

 bogs, the altered vegetation there found appears to be a step on the 

 way from the ordinary forms of vegetable tissue to coal. The follow- 

 ing table 3 shows the composition of wood, peat, and various types of 

 coal. From a comparison of this table with the preceding, it is not 

 difficult to understand how vegetable matter is converted into coal 



Carbon. Hydrogen. Oxygen. Nitrogen. 



1. Wood 49.66 6.21 43.03 1.10 



2. Peat 59.5 5.5 33.0 2.0 



3. Brown coal 68.7 5.5 25.0 0.8 



4. Bituminous coal. . 81.2 5.5 12.5 0.8 



5. Anthracite 95.0 2.5 2.5 0.0 



If the vegetable matter, after having been accumulated to great 

 depths and after having been partially altered, say to the condition 

 of peat, were buried beneath beds of mud or sand, it would undergo 

 further changes, both chemical and physical, tending to bring it nearer 

 and nearer to the condition of coal. The oxygen of the air would 

 then be more effectually excluded, and the chemical changes more 



1 After Le Conte, Elements of Geology. 



2 The composition of cellulose is usually given as C 6 H 10 O 5 or some multiple of this 

 The changes can be developed equally well from this formula. 



3 Le Conte, op. cit. 



