TRANSAt!TIONS OF SECTION C. 



625 



the nodules frequently split internally, and the fissures of retreat, filled with 

 calcite, blende, pyrites, or other mineral, constitute septa, or diyisiona, in the 

 septarium or septarian nodule. The so-called ' beetle-stones ' are septarian nodules 

 broken across, showing a central and diverging lines. 



The iron-ores of South Wales are fully treated of in the ' Memoirs Geol. Surv.,' 

 Iron-Ores, Part III., 1861, by E. Rogers, and their fossils by J. W. Salter. From 

 official sources we learn that the details of Production of Ironstone, chiefly Argil- 

 laceous Carbonate from mines under the Coal-mines Regulation Act, for the year 

 1889 were— 



In Mr. J. P. Lesley's ' Manual of Coal,' &c., 8vo., Philadelphia, 1856, at pp. 22, 

 &c., the variations in shales, and their passage even into coal, as the proportion of 

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

 detailed. 



Coal, Mather-coal, Coal-balls, ^x. — The coal itself, to which the shales (' batts,' 

 'binds,' &c., 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 laminte 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 laminte, 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 laminae, 

 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 and 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 v/ater and carbonic acid. . . . Under water, 

 or imbedded in aqueous deposits, the principal loss consists of carbon and oxygen ; 

 and the resulting 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 (may be that of the 

 rainy 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 sufficiently covered 

 ' Dawson, Quart. Joiirn. Geol. Soc, vol. xv., 1859, pp. 627, &c. 



1891. S S 



