PRIMARY COAL-FIELDS. 151 



can scarcely be ignited, to clear bituminous searns that 

 burn leaving scarcely a trace of ashes ; and fitted for 

 every economical purpose household fuel, gas -making, 

 oil -distillation, steam -raising, smelting, and metal- work- 

 ing. Like other coals, the thickest, the purest, and most 

 continuous seams have evidently grown and accumulated 

 in situ; those imbedding stony and earthy layers have 

 been interrupted in their accumulation ; and others, again, 

 less regular and continuous in thickness and mingled 

 more with extraneous impurities, have apparently been 

 formed of drift and water-logged vegetation. In lakes, 

 in estuaries, and along great shallow sea-reaches, the flora 

 of the Carboniferous era flourished for ages, the land now 

 sinking, now rising, but on the whole subsiding, to receive 

 the vast thickness of sediments which compose the system. 

 Read in the light of what is now taking place at the present 

 day, there is nothing abnormal or preternatural in the 

 Coal-formation, and we behold in its various coals merely 

 the peat - growths, swamp - growths, jungle -growths, and 

 vegetable-drifts of the period, compressed and mineralised 

 during the lapse of ages. The caking-coals, splint-coals, 

 cannel-coals, and anthracites or stone-coals of the miner are 

 merely different expressions of this mineralisation or meta- 

 morphism different conditions of deposit, as rapid covering 

 up, exposure to decay, nature of vegetation, and compact- 

 ness of overlying strata, all affecting the ultimate quality 

 of the coal. If much earthy matter has mingled with the 

 vegetable mass during its aggregation, the coal will be stony 

 and impure ; if the vegetable mass has been rapidly covered 

 up by retentive muds and clays (now converted into shales 

 and fire-clays), the coal will likely be soft and highly bitu- 

 minous ; if the superincumbent stratum be open and porous, 

 so as to admit the escape of volatile matters, the coal will 

 in all likelihood be hard, dry, and less bituminous ; and if 



