566 Reports and Proceedings — 



"^^illiamson, Carruthers, Balfour, Huxley, E. T. Newton, Orton, Dawson, Eheinsch, 

 Wethered, Bennie, Kidston, and others). Mr. E. Wethered has suggested that the 

 chief material in common coal was derived from the spores of a water-plant nearly 

 allied to Isoetes, and that woody material has supplied but little of the hydrocarbon. 

 He objects to the theory of "submerged forests" because of the difficulty that 

 Professor Dana has described, resulting in the calculation that for a four-foot seam 

 of coal there would be required a thickness of 32 feet of accumulated forest 

 vegetation and 48 feet for four feet of anthracite.^ The macrospores of Isoetes 

 lacustris have been found in the mud dredged in Loch Coulter, Stirlingshire, by 

 Mr. Thomas Scott.2 



" Dawson is disposed to think that the tuberin of cork, of epidermis in general, 

 and of spore-cases in particular, is a substance so rich in carbon that it is very near 

 to coal, and so indestructible and impermeable to water that it has contributed more 

 largely than anything else to the mineral." ^ Presfcwich refers to these, and especi- 

 ally to gums and resins, as main constituents of the coal ; and argues that the climate 

 was warm and moist, with a larger percentage of carbonic acid than exists at the 

 present day, and a more rapid plant -growth.* 



Messrs. Bennie and Kidston^ have not only carefully given the botanical history 

 of Lepidodendron and Sigillaria, and of their fructification, but have described the 

 spores met with in their examination of the Scotch Carboniferous strata, and have 

 given their conclusions as to the nature and condition of the beds from which the 

 spores were collected. The splint and parrot coals yielded most ; the cherry or soft 

 coals are too far bituminised to show them clearly, though present. Some fireclays 

 yield them in the upper two or three inches. Some thin shales (plant-beds and 

 takes) yield spores, and some have plant-remains as well. "Carbonised wood was 

 common in all the poor or shale- like coals. . . . Some of the thin coals were 

 almost entirely composed of such carbonised vegetable matter." Fragments of 

 scorpions and eurypterids occur plentifully in some of the 'old soils' (fireclays). 

 The former, being land-animals, and probably adapted to a hot (or, at least, warm) 

 climate, are among the most interesting of the coal-fossils. 



Drift-coal. — Formerly, more so than now, it was thought by some that the coal 

 had been formed by the accumulation of drifted timber and floating masses of 

 vegetation in rivers and estuaries. There are several difficulties in the way of 

 this hypothesis. There would have been more ash in the coal, because the water 

 would shift and deposit sand and clay, together with rafts and grass islands ; and 

 the ash of pure coals agrees in relative quantity and composition with the earthy 

 matter naturally contained in plants (Green and others). How far a calculation 

 could be made as to a given quantity fif ash in coal, and the amount of mineral 

 matter belonging to plants, as a basis for proving the original quantity of woody 

 matter concerned in a given quantity of coal, would be difficult to determine, for 

 some of the original mineral constituents have been probably removed by per- 

 colating water. 



Professor Lesley " has calculated that the Mississippi could not supply by driftage 

 from the forests of its valley in 100,000 years wood enough for one of the Schuylkill 

 anthracite beds ; mineral sediments would also interfere with the results. Under 

 favourable conditions, he adds, tropical forests (Central Africa) and coast-swamps 

 (Florida, Guiana, India) would supply good and sufficient material. So also the 

 swamps of the ' Sunk country' of Arkansas and Louisiana, as well as the ' Great 

 Dismal Swamp ' in Virginia, for one set of conditions (Lyell) ; and the mangrove 

 jungles in the West Indies and elsewhere for another. 



Fireclay, widerclay, undercMff, underbed, seat-earth, seat stone, hottom-stone, 

 spavin, clunch, fake, pouncin. This is usually a dense clay,' but sometimes sandy, 



1 Journ. Roy. Microsc. Soc. ser. 2, vol. v. 1885, pp. 406-420. 



2 Report of the Fishery Board, 1890. 



3 Balfour, " Palffiontological Botany," 1872, p. 67. 

 * Geology, vol. ii. 1888, pp. 117-120. 



5 Proceed. Royal Phys. Soc, Edinburgh, vol. ix. 1886, pp. 82-117. 



6 ' Manual of Coal,' etc., 1856. 



' In examining microscopically the ultimate particles of some shales and under- 

 clays, Mr. W. M. Hutchings has discovered that these are composed of a 'micaceous 

 deposit,' in which there is some fragmental mica, but that the mass appears to con- 



