GEOLOGY OF THE BRISTOL COAL-FIELD. 345 



and carbonic acid, till practically nothing but carbon is left as 

 in Anthracite; when this change has only partially taken place then 

 we have lignite. The production of Coal from woody fibre, may be 

 explained in four ways, either separately or all at the same time, 

 the oxidation being varied under different circumstances. 



1 . By decomposition as Carbonic Acid and "Water. 



2. Do. do and Marsh Gas. 



3. Do. Marsh Gas and "Water. 



4. Do. Carbonic Acid, Marsh Gas and "Water. 



The latter being the most probable. The production of two of 

 our Coals from woody fibre, may be represented by the following 

 formulae — 



Kailsea Coal. 

 6 CHO + 60 = CHO + 2 CH + 12 CO + 17 HO 



6 10 5 2 22 18 4 2 2 



Cellulose Oxygen Coal Marsh Gas Carbonic Acid Water 



Radstocb: Coal. 

 6 CHO + 20 = CHO + 2 CH + 8 CO + 16 HO • 



6 10 5 2 26 20 2 4 2 2 



Cellulose Oxygen Coal Marsh Gas Carbonic Acid Water 



"When wood has decayed, a small quantity of Humus is generally 

 formed which has the peculiar property of absorbing Ammonia, and 

 it is thus that the occurrence of Nitrogen in Coal is explained. 

 The Sulphur exists as Iron-pyrites or Gypsum. 



The following are analyses of a few specimens of Coal from the 

 Gloucestershire and Somersetshire seams. 



