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taining a high proportion of quite evident woody substances, and 

 brown coal where woody structure is not obvious. Small seams 

 of lignite occur in the freshwater and marine beds of the local 

 developments of the Bagshot and Bracklesham Series. Consider- 

 able masses were accumulated at Bovey Tracey on the borders of 

 Dartmoor in Oligocene times. Brown coals are widely distributed 

 on the Continent in Tertiary deposits and have been much ex- 

 ploited within recent years in Germany, where they are almost 

 as extensive as ordinary black coals. 



Sapropelic coals comprise an interesting type. The Cannel 

 coals, Bogheads and Torbanites differ from ordinary humic coals 

 not so much in appearance as in the high proportion of volatile 

 hydrocarbons they yield on distillation. Scottish boghead gave off 

 15,000 feet of hydrocarbon gases and 60 to 70 gallons of oil per 

 ton, and left a considerable amount of ash. The evidence bear- 

 ing upon the question of the origin of coals of this type so far 

 as it goes indicates that they accumulated under water, either of 

 lakes or quiet seas some little distance from the shores, as fine silt of 

 well macerated plant structures mixed with material derived from 

 molluscs, fish, etc., that inhabited the waters as well as with 

 varying proportions of clayey mud. At the present time richly 

 gaseous peat-mud accumulates in this way on the floor of tarns 

 and lakes. This group of coals, it is suggested, belongs essen- 

 tially to the same group of sediments as the oil-shales. 



Humic or Bituminous coals comprise the ordinary household 

 and steam coals of this country. The mother substance of this 

 group is undoubtedly organic and vegetable. In some uncommon 

 coals the structure of the composing vegetable material is still 

 plain, but more usually the only indications of vegetable origin 

 are either imprints upon the surface of associated seams of shale 

 or petrification in calcareous nodules scattered rarely in abund- 

 ance throughout the coal. Two theories of the origin of coal have 

 been long opposed : the 4 ' Growth in situ ' ' theory and the 

 " Drift " theory the one holding that the mother substance 

 accumulated where it now is much like modern peat, the other 

 that it was drifted varying distances by river floods and sea 

 currents away from the shore and becoming waterlogged sank 

 to the sea floor where it soon became covered by other sodden 

 rafts, and finally by sand and silt. The geography of the late 

 Carboniferous times was undoubtedly exceptionally favourable to 

 the accumulation and preservation of vegetable organic material. 

 The continents at that time were apparently of low relief; the 

 great activities of denudation during the Devonian period having 

 abased the highlands previously uplifted to wide low-lying pene- 

 plains. Extensive coastal plains with vast peat moors of various 

 types, including wood swamps, on the water sodden levels, fringed 

 the slightly higher lands. Slight disturbances of the sea level 

 would in such a case cause considerable disturbance on the low- 

 land fens ; either submerging them or allowing the currents to 

 remove the peat elsewhere. Possibly considerable numbers of 



