BITUMINOUS COALS 191 



The components seen as patches in the horizontal cleavages and 

 the thin black bands seen in the vertical sections are identical. — -The 

 next question arises, "Are the components seen as patches on 

 the horizontal cleavage surfaces as shown in Figure 4 and the 

 black, thin bands seen in cross-sections of the 'dull coal' as 

 shown in Figures i and 2, and Figures 7 and 10, identical?" This 

 question can also be definitely answered in the affirmative. A 

 piece of coal, small enough to be placed under a dissecting micro- 

 scope, may be split horizontally with a sharp tool through any 

 desired lamina; and when thus carefully manipulated it may 

 easily be shown that the black bands seen in the cross-section 

 are the thin, flat components seen on the horizontal cleavage 

 surfaces. 



The thin black bands are anthraxylon. — On account of the woody 

 structure present on the surfaces of these components, it must at 

 once be inferred that they are also derived from fragments of 

 woody tissues. The correctness of this inference must be demon- 

 strated so as to leave no doubt. 



Correlation of opaque sections with thin sections. — In order to 

 make the demonstration easier and more convincing it is desirable 

 to correlate the appearance of the opaque surfaces of the coal, 

 either at macroscopic observation or at a low magnification in which 

 the characters have already become famiKar, with the appearance 

 of thin sections observed by means of transmitted Ught. 



Figure 7 represents the appearance of the cross-section of "dull 

 coal" of an Illinois coal as seen by means of transmitted light 

 at a low magnification. This should be compared with Figure 2, 

 previously referred to, taken from an opaque section of the same 

 sample of coal and at the same magnification, but by means of 

 reflected light. The darker bands in Figure 2, which have been 

 shown to be the components seen as patches on the horizontal 

 cleavage surfaces, correspond to the lighter, more homogeneous- 

 appearing bands interlayered by the heterogenous-appearing 

 laminae shown in Figure 7. 



Figure 7 shows numerous strips of thin "bright coal." Figure 8 

 shows a part of the same at a much higher magnification and plainly 

 shows plant structure in all, but particularly in the strip a-i. 



