J. W. Dawson on > 



indicate that their occurrence is accidental rather than essential 

 to coal accumulation, and that thej are more hkely to liave 

 been abundant in shales and cannel coals, deposited in ponds or 

 in shallow waters in the vicinity of Lycopodiaceoiis forests, 

 than in the swampy or peaty deposits which constitute the 

 ordinary coals. It is to be observed, however, 'that the conspic- 

 uous appearance which these bodies and also the strips and 

 fragments of epidermal tissue, which resemble them in texture, 

 present in slices of coal, may incline an observer, not having 

 large experience in the examination of coals, to overrate their 

 importance, and this I think has been done by most microscop- 

 ists, especially those who have confined their attention to slices 

 prepared by the lapidary. One must also bear in mind the 

 danger arising from mistaking concretionary accumulations of 

 bituminous matter for sporangia In sections of the bitumin- 

 ous shales accompanying the Devonian coal above mentioned, 

 there are many rounded yellow spots, which on examination 

 prove to be the spaces in the epidermis of Psilophyton through 

 which the vessels passing to the leaves were emitted. To these 

 considerations I would add the following, condensed from my 

 paper above referred to, in which the whole question of the 

 origin of coal is fully discussed.* 



The mineral charcoal or "mother coal" is obviously 

 /_ tissue and fibers of bark ; the structure of the varieties 

 vhich and the plants to which it probably belongs, I havt 

 discussed in the paper above mentioned. 



(2.) The coarser layers of coal show under the microscope a 

 confused mass of fragments of vegetable matter belongmg to 

 various descriptions of plants, and including, but not usually 

 largely, sporangites. 



(3.) The more brilliant layers of the coal are seen, when sep- 

 arated by thin laminse of clay, to have on their surfaces m 

 markings of Sigillarise and other trees, of which they endentiT 

 represent flattened specimens, or rather the bark of such speci- 

 mens. Under the microscope, when their structures are pre- 

 served, these layers show cortical tissues more abundantly tn 



(4.) Some thin layers of coal consist mainly of flattened layers 

 of leaves of Cordaites or Pychnophyllum. .,, -^ 



(5.) The Stigmaria underclays and the stumps of bigi^^J ^^ 

 m the coal roofs equally testify to the accumulation ot coa . 

 iccessive foreSs. more especially, of Sigillan^; 





There is on the other hand no necessary connection ^y^^, ^^^ 

 gite beds with Stigmarian soils. Such beds are n^ore li^e 

 be accumulated in water, and consequently to constitute 

 minous shales and cannels. 



* See also Acadian Geology, 2d edit., pp. 138, 461, 493. 



