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trunks. Continuous beds were very seldom found ; they were generally 
broken across, or exhibited bands of clay or sands, at times so im- 
pregnated with bituminous matter as to render them capable of being 
burnt, 
The changes, by which wood, leaves, moss, and other vegetable 
substances were converted into coal required a long period of time, 
under chemical action of a peculiar nature. As many were aware, the 
chief constituents of all vegetable matter were the three substances, 
carbon, oxygen, and hydrogen ; the greater portion of the two latter 
occurring in the form of water, 
Besides these substances, a certain proportion of earthy and 
alkaline matter was also present. In some vegetables the proportion of 
water was so great as to reach as much as 90 per cent. of the whole 
plant, while the proportion of woody matter varied from 18 to 50 per 
cent. Pressure and exclusion from atmospheric air would get rid of 
the greater proportion of the water, while the carbon, if unable in the 
process of decay to combine with oxygen, would, with the alkaline and 
earthy matter, be preserved for an almost indefinite period. In time, 
the external appearance of the component vegetation would be lost 
and the texture be confused, though, in this condition, as was seen in 
the case of lignite, it would often retain the woody form for a very 
long time without alteration. A continuance of the chemical action 
would result in a change of the proportions of the gases and the 
mineral ingredients. 
Coal differed from wood, peat, lignite, &¢., in that it had parted 
with nearly all the other ingredients of vegetation except carbon, and 
it might be said to differ from all other minerals of which carbon was an 
essential element, by retaining in part and at intervals manifest indi- 
cations of its organic origin, in the presence of tissues and organs, 
which proved it to be composed of vegetable substances. It had some- 
times been difficult to draw the line between organic matter impreg- 
nated with mud and other impurities, and clay charged with organic 
matter derived from vegetation, by which it was rendered combustible. 
In the celebrated Scotch case, where permission to mine for coal was 
granted, an action was brought to restrain from working bituminous 
shale. It having transpired that the lessor considered it as coal, the 
case was decided in fayour of the lessee. About the same time bitu- 
