462 THE CARBONIFEROUS SYSTEM. 



other, the want of sufficient information in regard to the structures of 

 the plants known by impressions of their external forms in thert)ed3 

 of the Coal formation. Perplexed by the uncertain and contradictory 

 statements arising from these difficulties, and impressed with the 

 conviction that the coal itself might be made more fully to reveal its 

 own origin, I have for a long time been engaged in experiments 

 and observations with this object, and believe that I can offer definite 

 and certain results in so far as relates to the particular coals examined, 

 and, I have no doubt, with some slight modifications, to all the 

 ordinary coals of the true Coal measures. 



In ordinary bituminous coal, we recognise by the unassisted eye 

 laminae of a compact and more or less lustrous appearance, separated 

 by uneven films and layers of fibrous anthracite or of mineral charcoal, 

 and these two kinds of coal demand a separate consideration. 



The substance known by the very appropriate name of " mineral 

 chaixoal," consists of fragments of prosenchymatous and vasiform 

 tissues in a carbonized state, somewhat flattened by pressure, and 

 more or less impregnated with bituminous and mineral matters 

 derived from the surrounding mass. We cannot suppose that this 

 substance has escaped complete bituminization on account of its 

 original constitution ; for Ave have abundant evidence that this change 

 has passed upon similar material in various geological periods. A 

 substance so intimately intermixed with the ordinary coal cannot be 

 accounted for by the supposition of forest conflagrations or the action 

 of subterranean heat. The only satisfactory explanation of its occur- 

 rence is that afforded by the chemical changes experienced by woody 

 matter decaying in the presence of air, in the manner so well illus- 

 trated by Liebig. In such circumstances, wood parts with its hydro- 

 gen and oxygen and a portion of its carbon, in the forms of water and 

 carbonic acid ; and, as the ultimate result, a skeleton of nearly pure 

 charcoal, retaining the form and structure of the wood, remains. In 

 the putrefaction of wood under water, or imbedded in aqueous 

 deposits, a very different change occurs, in which the principal loss 

 consists of carbon and oxygen ; and the resulting coaly product con- 

 tains proportionally more hydrogen than the original wood. This is 

 the condition of the compact bituminous coal. This last may, by the 

 action of heat, or by long exposure to air and water, lose its hydrogen 

 in the form of hydro-carbons, and be converted into anthracite. In 

 all the ordinary coals we have the products, more or less, of all these 

 processes. The mineral charcoal results from subaerial decay, the 

 compact coal from subaqueous putrefaction, more or less modified by 

 heat and exposure to air. As Dr Newberry has very well shown, in 



