MODE OP ACCUMULATION OF COAL. 139 



arenaceous in composition, with little vegetable matter, and bleacbed 

 by tin' drainage from tikes 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 connexion 

 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 imbedded, and their wood had broken into cubical pieces of 

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

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

 of mineral charcoal occur on the surfaces of all the larger beds of coal. 

 None of these appearances could have been produced by subaqueous 

 action. (6.) Though the roots of Sigdlaria bear some resemblance 

 to the rhizomes of certain aquatic plants, yet structurally they are 

 absolutely identical with the roots of Cycads, which the stems also 

 resemble. Further, the Sigillarica grew on the same soils which 

 supported Conifers, Lepidodendra, Cordaites, and ferns — plants which 

 could not have grown in water. Again, with the exception, perhaps, 

 of some Pinnularice and Asterophyllites, there is a remarkable absence 

 from the coal measures of any form of properly aquatic vegetation. 

 (7.) The occurrence of marine or brackish-water animals in the roofs 

 of coal-beds, or even in the coal itself, affords no evidence of sub- 

 aqueous accumulation, since the same thing occurs in the case of 

 modern submarine forests. For these and other reasons, some of 

 which are more fully stated in the papers already referred to, while I 

 admit that the areas of coal accumulation were frequently submerged, 

 I must maintain that the true coal is a subaerial accumulation by 

 vegetable growth on soils wet and swampy, it is true, but not 

 submerged. I would add the further consideration, already urged 

 elsewhere, that, in the case of the fossil forests associated with the coal, 

 the conditions of submergence and silting-up which have preserved the 

 trees as fossils, must have been precisely those which were fatal to their 

 existence as living plants — a fact sufficiently evident to us in the case 

 of modern submarine forests, but often overlooked by the framers of 

 theories of the accumulation of coal. 



It seems strange that the occasional inequalities of the floors of the 

 coal-beds, the sand or gravel ridges which traverse them, the channels 

 cut through the coal, the occurrence of patches of sand, and the 

 insertion of wedges of such material splitting the beds, have been 

 regarded by some able geologists as evidences of the aquatic origin 



