564 



Reports and Proceedings — 



In Mr. J. P. Lesley's " Manual of Coal," etc. 8vo. Philadelphia, 1856, at pp. 

 22, etc., the variations in shales, and their passage even into coal, as the proporti<in 

 of carbonaceous (vegetable) matter increases by local conditions, are carefully 

 detailed. 



Coal, Mother-coal, Coal-halls, etc. — The coal itself, to which the shales (' batts,' 

 'binds,' etc., as they are variously termed) usually serve as a roof, or in which they 

 form ' partings,' or thin intermediate layers, comes next to be considered. Some 

 remarks on the different kinds of coal have already been made. Common black coal 

 is easily seen to be composed of thin alternate laminae of dull and bright material, 

 and usually the blocks or pieces have flat sides nearly at right angles with those 

 delicate layers of deposition. These faces are due to shrinkage-joints ; one is termed 

 the ' face' (as it is presented on the long edge of the seam exposed in working), or 

 the 'bord,' and the other or cross joint is the end; the former is also called the 

 ' cleat,' and this term is sometimes applied to both sets of joint -divisions. The 

 block of coal usually breaks also along the flat laminae, exposing a somewhat dull, 

 charcoaly surface, more or less interfered with by the next-lying bright lamina. The 

 dull parts are real charcoal, or decomposed wood, and soil the fingers when touched ; 

 whilst the bright, or hydrocarbon, portion keeps clean when dry. On the fire the 

 coal breaks more easily along the laminse, because the bright portion softens and 

 swells up with its bituminous change, and the ' mineral charcoal,' or ' mother-coal,' 

 keeps the portions distinct for a time ; so also the jointings open then, or give way 

 easily to the poker. 



The mineral charcoal may readily be seen to be flat fragments of woody tissue in a 

 carbonised state ; it is more or less impregnated with bituminous or mineral matter 

 from the associated beds, and retains the mineral matter of the original wood. It is 

 due to " the chemical changes experienced by woody matter in decay in the presence 

 of air," when "wood parts with its hydrogen and oxygen and a portion of its 

 carbon, in the forms of water and carbonic acid. . . . (Jnder water, or imbedded 

 in aqueous deposits, the principal loss consists of carbon and oxygen ; and the result- 

 ing coaly product contains proportionally more hydrogen than the original wood. 

 This is the condition of the compact bituminous coal." ^ 



The ' mother-coal ' necessarily indicates a periodical change (maybe that of the 

 ruiny season) in the formation of a coal-seam, for it lay exposed, as decaying wood, 

 whilst that which was accumulated just before must have been sufiiciently covered 

 up by water (a few inches may have been enough) to undergo the advanced chemical 

 changes causing a proportional increase of hydrogen. The dead sticks and stems 

 projecting out of and above the water-covered peaty mass below would naturally 

 supply the decaying touchwood and charcoal now lying as described above. 



Doubtless a progressive change in the elaboration of hydrocarbon soon took place 

 to some extent, even as it does in peat ; but probably it was not completed in the 

 compact coal until many layers of both vegetable and earthy matters had been 

 accumulated (the former in place, and the latter from inundation), and caused some 

 amount of pressure and consequent heat. 



As, under favourable circumstances, the bright coal can be seen to have been 

 made up of spores, leaves, branches, and stems of special trees, and other plants, 

 the place of growth must bave been a swampy forest or jungle, of enormous extent, 



1 Dawson, Quart. Journ. Geol. Sac, vol, xv. 1859, pp. 627, etc. 



