240 THE GROWTH OF COAL 



lonchiticd). The coal is coarse and earthy, with much epider- 

 mal and bast tissue, spore cases, etc., vascular bundles of ferns 

 and impressions of bark of Sigillaria and leaves of Cordaites. 

 It may be considered as a compressed vegetable soil resting on 

 a subsoil full of rootlets of Stigmaria." In this case the coal is 

 an inch in thickness, but there are many beds where the coal 

 is a mere film, and supports great erect stems of Sigillaria, 

 sending downward their roots in the form of branching 

 Stigmariae into the underclay, thus proving that the Stigmarise 

 of the underclays are the roots of the Sigillariae of the coals 

 and their roofs. 



Here is another example which may be called a coal group, 

 and is No. 1 1 of the same division : 



" Grey argillaceous shale, erect Calamites. 



Coal, i inch. 



Grey argillaceous underclay, Stigmaria, ift. 6in. 



Coal, 2 inches. 



Grey argillaceous underclay, Stigmaria, 4 in. 



Coal, i inch. 



Grey argillaceous underclay, Stigmaria. 

 " This is an alternation of thin, coarse coals with fossil soils. 

 The roof shale contains erect Calamites, which seem to have 

 been the last vegetation which grew on the surface of the upper 

 coal." 



Such facts, with many minor varieties, extend through the 

 whole eighty-one coal groups of this remarkable section, as 

 any one may see by referring to the paper and work cited in 

 the preceding note. It is possibly because in most coal fields 

 the smaller and commercially useless beds are so little open to 

 observation, that so crude ideas derived merely from imperfect 

 access to the beds that are worked exist among geologists. The 

 following summary of facts may perhaps serve to place the 

 evidence as to the mode of accumulation of coal fairly before 

 the reader : 



