242 THE GROWTH OF COAL 



when they existed as soils, rain water, and not sea water, per- 

 colated them. 



(5) The coal and the fossil trees 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 they 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 Sigillaria bear some resemblance 

 to the rhizomes of certain aquatic plants, yet structurally they 

 have much resemblance to the roots of Cycads, which the 

 stems also resemble. Further, the Sigillarice 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 Astero- 

 phyllites, and Rhizocarpean spores, there is a remarkable 

 absence from the coal measures of any form of properly 

 aquatic vegetation. 



(7) The occasional occurrence of marine or brackish- water 

 animals in the roofs of coal beds, or even in the coal itself, 

 affords no evidence of subaqueous accumulation, since the 

 same thing occurs in the case of modern submarine forests. 

 Such facts merely imply that portions of the areas of coal 

 accumulation were liable to inundation of a character so 

 temporary as not finally to close the process, as happened when 

 at last a roof shale was deposited by water over the coal. 

 Cannel coals and bituminous shales holding mussel-like shells, 

 fish scales, etc., imply the existence sometimes for long periods 

 of ponds, lakes or lagoons in the coal swamps, but ordinary 

 coal did not accumulate in these. It is in the cannels and 

 similar subaqueous coals that the macrospores which I 



