THE VEGETABLE MATTER OF ILLINOIS COAL BEDS 759 



vegetable material of the bog exposed during periods of unusual 

 low water. 



It seems to the writer that the explanation of mineral charcoal 

 as resulting from the temporary exposure and partial atmospheric 

 decay of the surface portion of the vegetable matter in the bog, 

 instead of the assumption that it must have been charred by fire, 

 is much more consistent with the following facts: (i) the frequent 

 repetitions of the dull laminae containing such large amounts of 

 mineral charcoal; (2) the larger number of plant spores in the 

 dull laminae than in the bright coal; (3) the numerous pinnae 

 and pinnules of ferns^ in the midst of the mineral charcoal 

 fragments; (4) the absence of layers of ash that would result from 

 the burning of the vegetable matter at the surface of the bog; and 

 (5) the changes that take place in the vegetable matter at the sur- 

 face of shallow marshes during periods of drought and exposure 

 at the present time. 



EXPLANATION OF THE BRIGHT AND DULL LAMINAE 



In explaining the origin of the bright and dull laminae, Dawson^ 

 maintained that it is the outer bark of flattened tree trunks that 

 alone formed the shining coal. In a recent paper on the origin 

 of bright laminae of coal, Pringle,^ of the Geological Survey of Great 

 Britain, reaffirms Dawson's view. 



The serious objection to this view is the fact that the bright 

 and dull laminae of the coal beds are so nearly parallel and are 

 often continuous for long distances. Trees that are overturned 

 in swamps fall in various directions, and their trunks lie across 

 one another at different angles. If the cortical portion of tree 

 trunks formed the bright laminae of coal, these bright laminae 

 would not be continuous for long distances, and the dull laminae 

 would be broken at short intervals by small areas of bright coal 

 representing the cross-sections and oblique sections of the cortical 



^ David White, Econ. GeoL, III (1908), 302. 



^ J. W. Dawson, "On the Conditions of the Deposition of Coal," Qiiar. Jour. 

 GeoL Soc, XXII (1866), 141. 



3 John Pringle, "On the Origin of Bright Laminae of Coal," Trans. Edin. GeoL 

 Soc.,X, Pt. I (1912), 33. 



