v.] 0^ THE FORMATION OF COAL. 103 



possess a specimen of what is called &quot; white coal&quot; from 

 Australia. It is an inflammable material, burning with 

 a bright flame, and having much the consistence and 



O O 



appearance of oat-cake, which, I am informed, covers a 

 considerable area. It consists, almost entirely, of a 

 compacted mass of spores and spore-cases. But the fine 

 particles of blown sand which are scattered through it, 

 show that it must have accumulated, subaerially, upon 

 the surface of a soil covered by a forest of cryptogamous 

 plants, probably tree-ferns. 



As regards this important point of the subaerial region 

 of coal, I am glad to find myself in entire accordance 

 with Principal Dawson, who bases his conclusions upon 

 other, but no less forcible, considerations. In a passage, 

 which is the continuation of that already cited, he 

 writes : 



&quot; (3) The microscopical structure and chemical composition of the 

 beds of can n el coal and earthy bitumen, and of the more highly bitu 

 minous and carbonaceous shale, show them to have been of the nature 

 of the fine vegetable mud which accumulates in the ponds and shallow 

 lakes of modern swamps. When such fine vegetable sediment is mixed, 

 as is often the case, with clay, it becomes similar to the bituminous 

 limestone and calcareo-bituminous shales of the coal-measures, (4) 

 A few of the under-clays, which support beds of coal, are of the 

 nature of the vegetable mud above referred to ; but the greater part 

 are argillo-arenaceous in composition, with little vegetable matter, and 

 bleached by the drainage from them of water containing the products 

 of vegetable decay. They are, in short, loamy or clay soils, and must 

 have been sufficiently above water to admit of drainage. The absence 

 of sulphurets, and the occurrence of carbonate of iron in connection 

 with them, prove that, when they existed as soils, rain-water, and not 

 sea-water, percolated them. (5) The coal and the fossil forests present 

 many evidences of subaerial conditions. Most of the erect and 

 prostrate trees had become hollow shells of bark before they were 

 finally embedded, and their wood had broken into cubical pieces of 

 mineral charcoal. Land-snails and galley-worms (Xylobius) crept into 

 them, and they became dens, or traps, for reptiles. Large quantities 

 of mineral charcoal occur on the surface of all the large beds of coal. 

 None of these appearances could have been produced by subaqueous 



