620 Reports and Proceedings — 



De la Beche's Memoir, after having presented some explanation of 

 geological phenomena, and treated of the general range and occurrence of 

 the Silurian and Devonian rocks in the southern moiety of Wales and the 

 South-western Counties of England, proceeds to describe the Carboniferous 

 strata, and at p. 143 takes up the Coal-measures ; and his work remains 

 a classic authority on the subject. De la Beche's account of these strata 

 has not been much modified, except by the descriptions of many additional 

 fossils, and details about the special characters of those then known. 



Other information, however, on the past and present conditions of the 

 South- West Coal-field is found in Mr. (now Sir) A. C. Bamsay's paper 

 " On the Denudation of South Wales and the adjacent English Counties," 

 in the same volume of 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 Beports, Proceedings, and Trans- 

 actions of the Scientific Societies of South Wales. 



3. Origin of Goal. — 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 fracture, 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 subsidences 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 arrange- 

 ment of the resulting flow of Carbonaceous mud. 



Mr. W. Galloway, in his memoir " On the Mode of Occurrence of Coal," * 

 carefully 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 carbonization 

 being on the same ground, following De la Beche's statements and con- 

 clusions ; 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. Grand'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 difterent 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 



1 The Coalfields of Great Britain, 4th edit. p. 81, etc. 



^ Report and Transactions of the Cardiff Naturalists' Society, vol. xvii. (for 1885), 

 1886, pp. 20-34. 



