THE GROWTH OF COAL 24I 



(i) The occurrence of Stigmaria under nearly every bed of 

 coal proves, beyond question, that the material was accum- 

 ulated by growth in situ, while the character of the sediments 

 intervening between the beds of coal proves with equal cer- 

 tainty the abundant transport of mud and sand by water. In 

 other words, conditions similar to those of the swampy deltas 

 of great rivers, or the swampy fiats of the interiors of great con- 

 tinents, are implied. 



(2) The true coal consists principally of the flattened bark 

 of sigillaroid and other trees, intermixed with leaves of ferns 

 and Cordaites, and other herbaceous debris, including vast 

 numbers of spores and spore cases, and with fragments of 

 decayed wood constituting "mineral charcoal," all their 

 materials having manifestly alike grown and accumulated where 

 we find them. 



(3) The microscopical structure and chemical composition 

 of the beds of cannel coal and earthy bitumen, and of the 

 more highly bituminous and carbonaceous shales, show them 

 to have been of the nature of the fine vegetable mud which 

 accumulates in the ponds and shallow lakes of modern swamps. 

 These beds are always distinct from true subaerial coal. 

 When such fine vegetable sediment is mixed, as is often the 

 case, with mud, it becomes similar to the bituminous lime- 

 stone and calcareo-bituminous shales of the coal measures. 



(4) A few of the underclays 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 in the chemical con- 

 dition in which we find such soils under modern bogs, and 

 must have been sufficiently above water to admit of drainage. 

 The absence, or small quantity of sulphides, and the occur- 

 rence of carbonate of iron in connection with them, prove that 



