TRANSACTIONS OF SECTION C. 625 



coal. It chiefly depended upon the amount of oxygen which could unite with the 

 carbon, forming carbonic acid, and the amount of hydrogen which could unite with 

 the carbon to form marsh gas. By this process oxygen and, hydrogen would pass 

 oft" in greater proportion than the carbon, thus increasing the proportion of the 

 latter to the whole. If, however, the submerging waters placed in contact with 

 the vegetable mass substances capable of supplying oxygen to the carbon, then 

 there would be a decrease in the proportion of the latter, and what the author 

 termed the ' fixed oxygen and hydrogen ' would increase in proportion to the 

 whole and give rise to a coal of a bituminous nature. 



With a view of ascertaining whether the chemical composition of the beds 

 overlying a seam of coal which has changed from bituminous to anthracite 

 also changed, the AVelsh ' nine feet ' seam was selected, which near Cardiff" is 

 semi-bituminous and at Aberdare becomes anthracitic. Specimens of the overlyino- 

 strata were selected from the two districts at each foot above the coal for five feet ; 

 these were analysed, and it was found that the beds from near CardiflP were con- 

 siderably more argillaceous and, as a whole, less ferruginous than those at Aber- 

 dare. It would be rash to attempt to determine the exact chemical nature of the 

 sediment deposited over the coal-forming vegetation in the two localities, as, with 

 the exception of silicate of alumina, the silicates and other minerals would have 

 undergone decomposition at the expense of the carbonic acid given off from the 

 coal-forming vegetation. There was, however, a decided change in the beds of the 

 two sections presented, which could not be ascribed to metamorphism. It rather 

 appeared to point to the sediment containing difl^erent constituents, which must 

 have had a very considerable eff'ect on the vegetable mass. It was to this that the 

 author was inclined to assign the change in the character of the coal. 



4. Preliminary RemarJcs on the Microscopic Structure of Coal. 

 Bij Professor W. C. Williamson, F.B.S. 



At the two first meetings of the British Association at York and Oxford in 

 1 831 and 1832, two papers were read on coal and coal-plants, by the late Henry 

 Witliam. Since that time comparatively little progress has been made in our 

 knowledge of the structure and physical composition of coal. Many local and limited 

 observations have been made by Dawson, Huxley, and others, but the results have 

 been indefinite if not contradictory. The author aims at bringing our knowledge 

 of coal to a more advanced state by commencing a systematic series of microscopic 

 observations of the coals of the entire world so far as he can obtain possession of 

 them. Many months of such observations have been devoted to the coals of 

 Eastern Scotland and to those of South Wales. These inquiries, thouo-h so 

 limited, have suggested the possibility of certain conclusions being ultimately 

 arrived at; but at present they are only advanced as hypothetical ones — though 

 they appear to be supported by the investigations already completed. A large 

 proportion of the coals examined contains mineral charcoal or mother coal in 

 various conditions ; sometimes the fragments are gathered together in thick layers 

 of considerable extent, at others they are thin and limited in their area. Frequently 

 separate fragments are isolated in the bituminous mass which encloses them. In a 

 large number of instances, portions of each fragment can readily be detached for 

 microscopic examination, but in many cases the fragments have become so con- 

 solidated and blended with the mass of the coal as to be incapable of such 

 separation. All these fragments exhibit a fibrous aspect when seen under low 

 powers, as opaque objects, but under lenses of higher power and with transmitted 

 light, they resolve themselves into two groups : one of these consists of frao-ments 

 of what are more or less bast-like, prosenchymatous tissues, and bear the aspect 

 of cortical structures. The others, on the other hand, belong to the fibro- 

 vascular group of tissues, exhibiting in the same minute portion of a fragment 

 various modifications of such tissues from those that are scalariform to fibres 

 with bordered discs. The most numerous are such as approach the latter more 

 nearly than the former type. These fibro-vascular structures bear no resemblance 

 1881. s s 



