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the subject of the origins of the various forms in which the element 

 is found in the earth's crust. We shall consider these in the 

 following order: the origin of coal, that of petroleums, that of 

 graphite, and that of the diamond. 



The Origin of Coal. 



Coals may be conveniently divided according to the supposed 

 mode of deposition of the mother substance according to the 

 following scheme : — 



Terrestrial. 



Peat (in part). 

 Lignites (in part). 

 Brown coal (in part). 



Lacustrine. 



Sapropelic coals (Cannel, Boghead and Torbanite). 



Lacustrine and Estuarine. 



Peat. 

 Lignite. 

 Brown coals. 



Humic or " Bituminous" coal. 



Of Uncertain Origin. 



Anthracite. 



Peat is a substance of recent accumulation, and in general 

 presents little or no difficulty on the question of origin. It is 

 further interesting because of the light its distribution and accum- 

 ulation throws upon the problem of the origin of some at least 

 of the older coals. 



Peat deposits occur on broad badly drained areas in the tem- 

 perate zones, at moderately high levels as on the Pennine moors 

 and at sea level on waterlogged coastal plains, as in the Fen and 

 Broads districts of East Anglia, in Ireland and on the North 

 German Plain. Three sharply defined types of peat are recog- 

 nised : (i) the Fen or Swamp peat, which is accumulated by fen 

 or swamp plants whose roots are bathed by the soil w r ater of 

 rivers or springs and are therefore supplied with a sufficiency of 

 mineral salts ; (2) the Moor peat, which is formed of the remains 

 of plants that are dependent for their water supply upon the almost 

 pure water of the atmosphere; and (3) the Transition peat, chiefly 

 of wood and grass remains of the vegetation in transition from the 

 fen to the moor. Fen peat is varied in composition, burns with a 

 bright flame and leaves a fair proportion of ash. Moor peat con- 

 sists largely of bog-moss, cotton grass, ling and similar heath 

 moor plants. Its flame in burning is hot and a smaller proportion 

 of ash is left. Peat is formed as the result of a process, called for 

 lack of a better term " peatification " ; as distinct from humifica- 

 tion as it is from decay, though in what the process consists is 

 practically unknown. An abundance of water, a lack of air, and a 

 comparative rarity of bacteria appear however to be factors. 



Lignites are conveniently considered as Lignites proper, con- 



