BITUMINOUS COALS 189 



become homogeneous and the lumena and the middle lamella 

 have been effaced. All possible degrees of preservation may be 

 seen between these two extremes. 



There can, therefore, be no doubt that the bright coal represents 

 components derived from larger pieces of woody tissues, such as 

 fragments of stems, branches, and roots now compressed and 

 flattened. In some cases these must have been of considerable 

 size. As it is derived from woody tissues (pieces of wood turned 

 into coal) and consists of definite units easily distinguishable from 

 the rest of the coal, it will be called ''anthraxylon," from the Greek 

 anthrax, coal, and xylon, wood. Bright coal then is synonymous 

 with anthraxylon. 



THE "dull coal" 



Having disposed for the present of the "bright coal" or larger 

 anthraxylon components, closer attention may now be given to the 

 so-called "dull coal" in which the "bright coal" appears to be 

 embedded. It has already been shown when seen in cross-section, 

 that it consists mainly of two kinds of material; thin black bands 

 interlayered by a Hghter-colored granular-appearing matter 

 (Figs. I and 2). The "dull coal" may, therefore, conveniently 

 be divided into two classes : the thin black strips and its embedding 

 matrix, the attritus. 



The dull coal as seen in horizontal cleavage surfaces. — When hori- 

 zontal cleavage surfaces of any compact coal are examined, a 

 varying number of patches showing woody structures are observed 

 to be distributed over the entire surfaces, surrounded more or less 

 by structureless areas (Fig. 4). These patches vary considerably 

 in size, form, and number. But usually they are relatively small 

 and vary within certain Umits. This condition is best illustrated in 

 Figure 4, representing a cleavage surface of the coal from the 

 Vandaha mine, near Terre Haute, Indiana. It represents a hori- 

 zontal fracture through perfectly compact coal and only a very 

 few of the patches seen represent mineral charcoal. Since this 

 coal spHts very readily in any desired plane, very many thin sheets 

 may be obtained and thus many horizontal cleavage surfaces may 

 be produced for observation. All reveal appearances very similar 



