COAL 



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with equally minute plates of impure coal, containing a small admixture of finely- 

 divided earthy matter. These subdivisions, differing in their lustre and fracture, are 

 frequently of excessive thinness, the less brilliant leaves sometimes not exceeding the 

 thickness of a sheet of paper, In many of the purer coal-beds these thin partings 

 between more lustrous layers consist of little laminae of pure fibrous charcoal, in 

 which we may discover the peculiar texture of the leaves, fronds, and even the bark 

 of the plants which supplied a part of the vegetable matter of the bed. All these ulti- 

 mate divisions of a mass of coal will be found to extend over a surprisingly large 

 surface, when we consider their minute thickness. Pursuing any given brilliant 

 layer, whose tliickness may not exceed the fourth part of an inch, we may observe it 

 to extend over a superficial space which is wholly incompatible with the idea that it 

 can have been derived from the flattened trunk or limb of any arborescent plant, 

 however compressible. When a large block of coal is thus minutely and carefully 

 dissected it very seldom, if ever, gives the slightest evidence of having been produced 

 from the more solid parts of trees, though it may abound in fragments of their fronds 

 and 1 deciduous extremities. 1 



It is not possible within the space which can be afforded to this article in the 

 present work, to examine further the various views which have been entertained by geo- 

 logists and chemists of the formation of coal. A brief summary must now suffice : 



1 . Coal is admitted upon all hands to be of vegetable origin. 



2. Many refer coal to some peculiar changes which have taken place in wood ; 

 others to the formation and gradual subsidence of peat bogs ( Unger). Fuci have also 

 been thought by some to supply the materials for coal-beds. 



3. By some the coal is thought to be formed upon the spots on which the trees grew 

 and decayed. By others it is supposed that vast masses of vegetable matter were 

 drifted into lakes or deltas, to be there decomposed. 



4. Whether the plants grew on the soil the under clay upon which the coal is 

 found, or were drifted to it ; there must have been long periods during which nothing 

 but vegetable matter was deposited, and then a submergence of this land, and vast 

 accumulations of mud and sand. The number of coal-seams in some of our coal-fields 

 and the thicknesses of the strata will be given. 



Professor Henry Eogers and others suppose, that the whole period of the coal-measures 

 was characterised by a general slow subsidence of the coasts on which we conceive that 

 the vegetation of the coal grew ; that this vertical depression was, however, inter- 

 rupted by pauses and gradual upward movements of less frequency and duration, and 

 that these nearly statical conditions of the land, alternated with great paroxysmal 

 displacements of the level, caused by the mighty pulsations of earthquakes. (See 

 FAULTS, HEAVES.) 



The difficulties are mainly the facts 



1. That the evidence is not clear that anything like ligneous structure can bo 

 detected in coal, while microspores and macrospores are sometimes found in abundance. 



2. That the woody matter found in coal is never converted into coal, although 

 sometimes it appears as if the bark was so changed. 



3. That the coal arranges itself always in exact obedience to the underlying surface, 

 as though a semi-fluid mass had been spread out on a previously-formed solid bed. 



4. The thinning out of true coal to extreme tenuity, as mentioned by Professor 

 Henry Rogers ; numerous examples of which appear in this country. 



5. The extreme difficulty connected with the subsidence of the surface of the earth 

 to such a depth as that to which the lowest seams of coal extend. 



We do not intend to answer any of these difficulties, but to leave the question 

 open for further examination ; merely remarking, in conclusion, that there can be 

 no doubt of the vegetable origin of coal. The only question is, the conditions of 



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