274 The Origin and Relations of the Carbon Minerals. 



wliicli may be observed in making a vertical section of a peat- 

 bog, or in comparing the coals of Tertiary, Mesozoic and Car- 

 boniferous age, only the latter is the continuation and natural 

 sequence of the former series of changes. 



In the Laurentian rocks of Canada are large accumulations of 

 carbonaceous matter, all of Avhich is graphite, and that which 

 is universally c(mcedecl to be derived from plant-tissue. The 

 oxidation of graphite is artificially difficult, and in nature's la- 

 boratory slow ; but it is inevitable, as we see in the decomposi- 

 tion of its outcrops and the blanching of exposed surfaces of 

 clouded marbles, where the coloring is graphite. Thus the end 

 is reached, and by observations in the field, the origin and re- 

 lationship of the different carbon solids derived from organic 

 tissue are demonstrated. 



It only remains to be said, in regard to them, tliat all the 

 changes enumerated may be imitated artificially, and that the 

 stages of decomposition which we have designated by the names 

 graphite, anthracite, coal, lignite, are not necessary results of 

 the decomposition of plant-tissue. A fallen tree may slowly 

 consume away, and all its carbonaceous matter be oxidized and 

 dissipated without exhibiting the phases of lignite, coal, etc. ; 

 and lignite and coal, when exposed to air and moisture, are 

 burned away to ashes in the same manner, simply because in 

 these cases complete oxidation of the carbon takes place, particle 

 by particle, and the mass is not affected as a wliole in such a 

 way as to assume the intermediate stages referred to. Chemical 

 analysis, however, proves that the process is essentially the same, 

 although the physical results are different. 



Evolved Pkoducts. 



The gradual wasting of plant-tissue in the formatiou of peat, 

 lignite, coal, etc., may be estimated as averaging for peat 20 to 

 30 per cent. ; lignite, 30 to 50 per cent. ; coal, 50 to 70 per 

 cent. ; anthracite, 70 to 80 ; and graphite, 90 per cent, of the 

 original mass. The evolved products ultimately represent the 

 entire organic portion of the wood — the mineral matter, or ash, 

 being the only residuum. These evolved products include both 

 liquids and gases, and by subsequent changes, solids are pro- 



