THE VEGETABLE MATTER OF ILLINOIS COAL BEDS 755 



regularity of thickness of the coals^the Herrin (No. 6) bed ranges 

 from 7 to 9 feet over a known area of at least 5,000 square miles. 

 A thin band of shale or shaly coal (''blue band"), one-half to two 

 inches thick, is present 18-24 inches above the floor of this coal 

 over practically the entire area of its distribution, and the thickness 

 of the benches above and below the "blue band" is remarkably 

 uniform. The Springfield (No. 5) bed, also, scarcely varies one 

 foot in thickness over more than 5,000 square miles; (3) the small 

 percentage of mineral matter or ash in the coal shows that very 

 little mud and sand sediments were mixed with the plant remains 

 as they accumulated. 



In times of flood the amount of mud and sand carried by streams 

 is so great compared with the amount of vegetable matter, and the 

 latter is deposited so irregularly, that it can scarcely be imagined 

 how the plant material of these coal beds could have been carried 

 by streams into the Illinois basin, and have accumulated in practical 

 continuity over such extensive areas, in anything like such uniform 

 thickness, and with so little mingling of mineral sediments. Exten- 

 sive areas of relatively pure vegetable matter are known to be 

 accumulating in swamps at the present time, but there is no known 

 place where plant remains transported by streams during floods 

 are accumulating as a continuous bed over any considerable area in 

 anything approaching regularity of thickness and without a very 

 large mixture of sand and mud; nor does it seem probable that pure 

 transported vegetable deposits have ever accumulated over any 

 considerable area in the past. 



From a study of the small coal basins of France in recent years 

 Fayol, supported by De Lapparent and other French geologists, 

 has revived the transport theory of accumulation of the vegetable 

 matter of coal beds. However, practically every geologist who 

 has studied extensive coal beds, especially those of the Appalachian 

 region of the United States, with which the coal beds of Ilhnois 

 are comparable, has rejected the transport theory of accumulation 

 as appHed to those beds. Rogers Brothers, Lesquereux, Dawson, 

 Andrews, Dana, Orton, Stevenson, White, and Ashley have all 

 accepted the growth-in-place theory of accumulation of the vege- 

 table matter of extensive coal beds as the only one that is consistent 



