CONVERSION OF VEGETABLE MATTER INTO COAL. 119 



and owing its compactness to the peculiar circumstances under which 

 it has been formed, the changes it may have subsequently undergone, 

 and the substances intermixed with it. The power of yielding naph- 

 tha by distillation, is the distinction between one end of the series 

 and the other. The last link (anthracite) contains only carbon ; so 

 the last result of the distillation of asphaltum is also carbon. 



To convert wood-coal or jet into true coal, some further process 

 than long submersion in water seems necessary. The latter sub- 

 stance, jet, was reduced to powder by Dr. M., put into a gun-barrelj 

 and covered with Stourbridge clay ; it was then exposed to a mode- 

 rate red heat. By this process, it was converted into a substance 

 having all the external characters and chemical properties of true 

 mineral coal, and the clay was converted into coal shale. But though^ 

 in the laboratory of the chemist, the last stage of the formation of 

 coal requires artificial fire, yet in the great laboratory of Nature, ve- 

 getable fermentation and compression may evolve sufficient heat, for 

 the ultimate formation of mineral coal. It may however deserve 

 notice, that most great repositories of coal are intersected by beds 

 and dykes of basalt, which is now admitted to be of igneous origin.* 



Pressure and time may be alone sufficient to produce the destruc- 

 tion of vegetable organization, and the perfect consolidation of beds 

 of coal, as is proved by the complete consolidation of loose materials 

 left in coal mines, when the supports are removed, and the upper 

 strata sink down. In a few years, scarcely a trace of former ope- 

 rations remains. In contemplating natural causes, we are too apt to 

 measure their power by the results of artificial processes, and by ob- 

 servations continued for a short portion of human life. The substan- 

 ces found in the neglected vessels of the chemist, often prove to us 

 that changes in the physical properties of bodies are effected by time, 

 which it would be difficult to imitate in common experiments. 



The great regular coal formation appears to be confined to the 

 lower secondary strata, generally resting on transition limestone. In 

 some situations the under transition rocks are wanting, and the series 

 of coal strata rests on granite, with the intervention of a thick bed of 

 conglomerate. 



No mineral coal, both good in quality and abundant in quantity, has 

 ever been found either in the primary or in the lower transition rocks 

 ot in the upper secondary or the tertiary strata. It is true, that in 

 the oolite of the upper secondary strata, two series of coal strata oc- 

 cur on the eastern moorlands of Yorkshire, which are thought of 

 sufficient importance to be worked ; but the coal is very indifl^erent, 

 and is used chiefly by the lime burners. This coal formation will be 



* At Meisner, in Hesse, a thick bed of wood-coal or ligfnite is covered by an 

 enormous mass of basalt, and is separated from it only by a thin bed of clay. 

 The upper parts of the lignite are converted into anthracite, and even into true 

 bituminous coal, while the lower parts are formed of earthy and fibrous wood-coal. 



