106 ILLINOIS ACADEMY OF SCIENCE 



current agency of such widespread action is change in the 

 water level of the basin during the time the vegetable material 

 was accumulating. 



If it is assumed that the dull laminae resulted from the 

 flooding of the basin, we should have associated with the dull 

 laminae a considerable percentage of mud deposited during 

 such times of flood. We are not left to speculate with regard 

 to the effects of flooding of a basin during the progress of ac- 

 cumulation of the vegetable matter of the coal, for we have 

 such an example in the clay band or "blue band" of the Herrin 

 (No. 6) coal, which extends over practically the entire area of 

 its distribution, and is clearly a mud parting due to flooding. 

 Black shale partings common in portions of some coal beds, 

 as in coal No. 1, in Illinois are also records of flooding of the 

 marshes during the time of accumulaton of the vegetable mat- 

 ter. The typical dull laminae and mineral charcoal zones in 

 the large coal beds of Illinois, as elsewhere, are not such mud 

 partings. They usually contain only a slightly, if any, greater 

 percentage of ash than the bright bands, and are practically 

 free from clay silt. They contain a relatively smaller per- 

 centage of volatile matter and a larger proportion of fixed car- 

 bon than the bright bands. It will be seen from the following 

 table, in which a number of proximate analyses of mineral 

 charcoal are compared with analyses of average coal from the 

 same beds, that in general the mineral charcoal contains only 

 a little if any more ash than the average coal of the bed in 

 which it occurs. 



After discussing the original amount and the composition 

 of the ash contained in living species of such types of coal 

 plants as lycopods, ferns and equisetae, Stevenson 1 concludes 

 that "one should expect to find in ordinary (pure) coal not 

 much less than 6 per cent of ash, or even more, in which silica 

 and alumina should predominate greatly." He thinks it prob- 

 able that coals containing less inorganic matter than the plant 

 substance should have yielded, have had some of the original 

 inorganic content removed by solution in ground water. It is 

 probable that some coals which locally contain more than the 

 original amount of inorganic matter, as pyrite lenses, etc., have 

 been situated in places favorable for deposition of minerals 

 rather than solution, and in this way have become enriched in 

 their mineral content. In many places also a small percentage 

 of the inorganic constituents of the coal above that originally 

 present in the plants, may have come from wind-blown dust 



1, Stevenson, J. J. The Formation of Coal Beds; Proc. Am. Phil. Society, vol. 

 LIL, 1913, p. 107. 



