BITUMINOUS COALS . 187 



"bright coal," and the bands d-2, d-4, d-6, and d-S represent "dull 

 coal." The lettering in Figure i and Figure 2 correspond. It 

 may readily be seen that the bands of "dull coal" are compiled of 

 thin black strips which have a black ghstening appearance in the 

 coal, interlayered by a lighter-colored matter which has a dull 

 grayish appearance in the coal and is of a rather uniformly granular 

 nature. 



All ordinary bituminous coals thus far examined are similar 

 in this respect and any coal might have been chosen equally well to 

 illustrate this condition. 



THE "bright coal" 



Since the term "bright coal" or its equivalent "glanz coal" 

 is applied to a definite component in coal and has become perma- 

 nently embodied in the literature, the matter must be treated as a 

 separate subject. In speaking of "glanz coal" or "bright coal" 

 it becomes necessary to limit this des* -nation to those bands or 

 components easily recognizable with the unaided eye, such as are 

 designated by a in Figures i and 2. Such a limitation draws an 

 arbitrary Hne between the larger bands easily visible and the thinner 

 ones not so easily distinguishable, and comprising a part of the 

 "dull coal" as already indicated. There is no hard-and-fast 

 hne between the two. It is with this restriction that the concept 

 of "bright coal' or "glanz coal" is used at this time. 



The question that is constantly raised and that must be defi- 

 nitely answered is, "What are the bands of "bright coal" and what 

 is their origin?" In an examination of Figure i, although repre- 

 senting but a small piece of coal, it will be seen that a number of 

 the bands of "bright coal" taper off on one end. When a larger 

 block is examined many more will be found to do the same and 

 several may be found to taper off on both ends; and when a very 

 large block or a bank of coal is examined closely almost all, if 

 not all, of the bands of "bright coal" are found to taper off on 

 either end. It may be necessary to follow some of the bands for a 

 considerable distance, many feet possibly, but eventually they 

 terminate in a similar manner. Finally when these are examined 

 in all lateral directions, it can be shown that they taper off in all 



