102 ILLINOIS ACADEMY OF SCIENCE 



Brothers, Lesquereux, Dawson, Andrews, Dana, Orton, Stev- 

 enson, White, and Ashley, have all accepted the growth in place 

 theory of accumulation of the vegetable matter of extensive 

 coal beds as the only one that is consistent with the facts. It 

 is safe to assume, then, that the vegetable matter of the 

 coal beds of Illinois accumulated practically in the places where 

 the plants grew. 



The acceptance of the growth-in-place theory of accumula- 

 tion does not settle the question whether the basins bordered 

 the sea, as lagoons, or occupied broad depressions over coastal 

 plains, as the Dismal Swamp, or covered large areas over river 

 flood plains; nor is it purposed to discuss this phase of the 

 question at this time. The fact that the vegetable matter of 

 coal beds accumulated under water in the places where the 

 plants grew does not prove that the water was ever more than 

 a few inches, or at most a very few feet in depth, even where 

 coal beds 5 to 10 feet thick have been formed. On the con- 

 trary the structural features of the coal beds indicate conclu- 

 sively that the water in which the vegetable matter accumulated 

 was very shallow as well as that it was very quiet. 



STRUCTURAL FEATURES OF THE COAL BEDS 



One of the more conspicuous structural features of the coal 

 beds of Illinois, which are representative of the larger beds 

 everywhere, is their stratification, the more prominent bedding 

 planes being 3 to 5 or more inches apart. These bedding planes 

 form partings along which the coal separates rather easily, 

 and they usually show well-developed bands of "mother coal," 

 or mineral charcoal. These stratification planes often become 

 more conspicuous when the bed is weathered, but some of them 

 are prominent on unweathered faces. Such a conspicuous clean 

 parting of mineral charcoal occurs 18 to 24 inches below the 

 roof of the Herrin (No. 6) coal over several hundred square 

 miles in western and southern Illinois, and appears to be al- 

 most co-extensive with that bed. Along this charcoal zone, 

 the coal separates so perfectly that where the overlying shale 

 does not stand well in the mines the coal above this parting is 

 left for a roof. Five or six inches lower is another mineral 

 charcoal parting, almost equally well developed and persistent. 



Between the more prominent partings and bedding planes, 

 the coal from roof to floor is made up of alternating bright and 

 dull laminae, which are usually y 2 to 1-32 of an inch thick, 

 although in places they are considerably thicker. The aggre- 

 gate dull bands generally make up nearly or quite one-half of 



