270 Tim Origin and Relations of the Qarhon Minerals. 



as many cliemical formulae as Ave like, and give them specific 

 names ; but it is evident tliat this is child's play, not science. 

 The truth is, the slowly decomposing tissue of the plants of past 

 ages has given us a series of phases which we have grouped un- 

 der distinct names, and we have called one gronp peat, one 

 lignite, another coal, another anthracite, and another grap)hite. 

 We have spaced off the scale, and called all within certain lines 

 by a common name ; but this does not give us a common com- 

 position fox all the material within these lines. Hence we see 

 that any efPort to define or describe coal, lignite or anthracite, 

 accurately, must be a failure, because neither has a fixed com- 

 position, neither is a distinct substance, but simply a conven- 

 tional group of substances which form part of an infinite and 

 indivisible series. 



But this sliding scale of solid compounds, which we designate 

 by the names given above, is not the only product of the natural 

 and spontaneous distillation of ])lant-tissue. Part of the origi- 

 nal organic mass remains, though constantly wasting, to rejDre- 

 sent it ; another part escapes, either completely oxidized as car- 

 bonic acid and water, or in a volatile or hquid form, still retaining 

 its organic character, and destined to future oxidation, known 

 as carburetted hydrogen, defiant gas, petroleum, etc. 



Hence, in the decomposition of vegetable tissue, two classes 

 of resultant compounds are formed, one residual and the other 

 evolved; and the genesis and relation of the carbon minerals may 

 be accurately shown by the following diagram. 



PLANT-TISSUE. 



Eesidual Products. 



Peat. 



I 

 Lignite. 



I 

 Bituminous Coal. 



Semi-bituminous Coal. 



Anthracite. 



Graphitic Anthracite. 



Graphite. 



Ash. 



Evolved Products. 



Carbonic Acid. 

 Carbonic Oxide. 

 Carburetted Hydrogen, etc. 

 Water. 



'Maltha. 



Petroleum. 



Asphalt, etc. 



Asphaltic Coal. 



I 

 Asphaltic Anthracite. 



