THE VEGETABLE MATTER OF ILLINOIS COAL BEDS 763 



Lesquereux^ described the changes that occur in the vegetable 

 matter at the surface of swamps during dry periods as follows: 



Wherever the growth of peat in submerged bogs is checked by dryness or 

 other causes the upper surface of the peat becomes crusted, hardened, and 

 transformed into a thin coating quite impervious to the entrance of any kind 

 of foreign matter, and it is upon this hard upper crust that the boggy humus 

 forms, or, whenever the land becomes resubmerged, a new peat vegetation 

 begins. In such cases such a crust remains as a parting between two layers 

 of peat. 



Von Gumbel in 1883 suggested: "It is very probable that in 

 occasional drying of the swamp, followed by renewal of flooding, 

 lies the explanation of the alternating bright and dull coal bands." 



In discussing the process of putrefaction of vegetable matter of 

 coal as described by Renault, David White^ says that if uninter- 

 rupted the process of putrefaction goes on until all the softer 

 tissues are disintegrated and decomposed, leaving only the most 

 indestructible parts, immersed in a dark subgelatinous, plastic, or 

 liquid mass, the fundamental matter. This fundamental matter 

 not only envelops the undestroyed woody matter, but it infiltrates 

 the surviving tissues to a greater or less extent. Where the impreg- 

 nation is complete, we find dense, glossy, and shining coal. In 

 many instances the impregnation has been imperfect, and some- 

 times intergrades to a charcoal or "mother of coal." 



It is thought by the writer that the oft-repeated lowering, 

 probably of only a very few inches, of the water level in the shallow 

 swamps, and the consequent exposure of successive levels of the 

 vegetable matter to the air, is the only adequate explanation that 

 accounts for the extensive bedding planes practically free from clay 

 sediments, the general distribution and alternation of the bright 

 and dull laminae, and the large amount of mineral charcoal in the 

 latter, as they occur in the coal beds of Illinois, the bright laminae 

 resulting from putrefaction entirely under water, and the duU 

 laminae and mineral charcoal resulting from partial atmospheric 

 decay previous to the more complete subaqueous putrefaction. 



* L. Lesquereux, Second Geological Survey of Pennsylvania, Ann. Rept. for 1883, 

 p. 118. 



^ David White, "Some Problems in the Formation of Coal," Econ. Geol., Ill 

 (1908), 303. 



