TRANSACTIONS OF SECTION C. 617 



the ' Memoirs of the Geological Survey ' ; and very much has been added by local 

 observers, as shown by numerous papers on this coal-field and its constituents in 

 the Reports, Proceedings, and Transactions of the Scientific Societies of South 

 Wales. 



3. Origin of Coal. — Coal is now generally accepted as being a compressed and 

 chemically altered mass of ancient vegetables. The tissue of some of the trees 

 and other plants may be detected in the substance more or less distinctly by frac- 

 ture, by burning, and in thin sections. In some cases trees occur rooted in the 

 attitude of growth, their stems rising upwards and their roots remaining in or 

 below the coal. The accumulation of coal as seams of varying thicknesses, in very 

 numerous parallel beds, can be explained by the gradual and long-continued sub- 

 sidence of long and wide tracts of old marginal sea-beds, estuaries, and lagoons, 

 with adjoining lands,' all more or less invested with vegetation. At the same time 

 limited, isolated, and lenticular patches and nests of pure coal, usually in sand- 

 stone, have been probably due to floating masses of vegetation, matted plants and 

 trees, becoming waterlogged and sinking in estuaries and shallow seas. 



Some highly bituminous coal, like cannel and torbanite, may have been due to 

 limited accumulations of macerated plants rotting in water ; or to the bursting of 

 those natural reservoirs, like peat-bogs, and a local arrangement of the resulting 

 flow of Carbonaceous mud. 



Mr. W. Galloway, in his memoir ' On the Mode of Occurrence of Coal,'- care- 

 fully places before his readers the two sets of opinions about the origin and 

 formation of coal. First, as to the place of growth and of carbonisation being on 

 the same ground, following De la Beche's statements and conclusions ; and, 

 secondly, as to the accumulation of vegetable matter, some dead and broken, some 

 already decomposed, derived from the forests and herbage of marshy lands, and 

 deposited in great lakes (as expressed by C. Graud'Eury in the ' Annales des 

 Mines,' 1882), with the Stigmarice living and dying as water-plants (as they were 

 at first regarded, and thought to have been formed of a central body and long- 

 spreading arms and leaves) ; while tall trees grew here and there on the water- 

 side, until, falling down, they lay prostrate in the black mud ; or, breaking ofi', 

 left their rotting stumps still standing upright. 



Mr. Galloway accepts the latter opinion to some extent, because he finds the 

 roots in underclays to have no direct communication with the coals above 

 them, — on account of the presence of persistent shaly layers, or 'partings,' 

 traversing coal-beds, and very intimately passing into the coaly matter itself, — on 

 account of a seam being cannel-coal, blackband-ironstone, and shale in dift'erent 

 parts of its extent, with a coal lying on it without an intervening underclay ; and 

 if this shows that a coal can have been formed without an underclay, he argues 

 that any underclay need not have been necessarily the soil of a coal-seam. He 

 acknowledges the subject to be one of difficulty ; and it seems to me that some at 

 least, if not all, of the difficulties have been already removed by De la Beche, 

 Lesley, Lyell, Dawson, and other observers. 



4. Area of the Coal-grotvth.—YoT knowledge of what ruled the local occur- 

 rence of coal, Tve owe a great debt to Mr. K. A. 0. Godwin-Austen, who had 

 studied the geology of the South-western Counties with De la Beche. To him 

 we are indebted for the approximate demarcation of the bounds and margins of 

 the Carboniferous Formations, particularly for the probable land-limits and 

 outward extension of the Coal-measures. In his valuable memoir ' On the 

 possible Extension of the Coal-measures,' ' he explained the reasons for his indicat- 

 ing on the map then communicated to the Geological Society the physical con- 

 figuration of North-western Europe at the close of the Palaeozoic Period, and the 

 outline of the surfaces which supported the coal-vegetation. He concluded to 



' The Coalfields of Great Britain, 4th edit., p. 81, &c. 



' BepoH and Transactions of the Cardiff Naturalists' Society, \o\.'SNi\. (for 1885), 

 1886, pp. 20-34. 



' Qtiart. Journ. Geol. Sac, vol. xii., 1866, pp. 38-73; also Beport Coal Commission, 

 1871, pp. 424 and 511, with plates ; and Bep. Brit. Assoc, for 1879, p. 227, plate 

 XIV. 



