756 T. E. SAVAGE 



with the facts. It seems 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 accumulation 

 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 5-10 feet thick have been formed. 

 On the contrary, the structural features of the coal beds indicate 

 conclusively that the water in which the vegetable matter accumu- 

 lated 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 3-5 

 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 

 20-24 inches below the roof of the Herrin coal over several hundred 

 square miles in western and southern Illinois, and appears to be 

 almost coextensive 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 bench above this parting is left for a 

 roof. Five or six inches higher 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 ^ to 3V of an inch thick, though in places 

 they are considerably thicker. The aggregate dull bands generally 



