BITUMINOUS COALS 205 



SUMMARY 



The bituminous coals consist of alternate layers of "bright" 

 coal and "dull" coal. The "bright" coal is called anthraxylon. 



The "bright" coal was formed from the large limbs and trunks 

 of trees or parts of them which were not disintegrated in the peat 

 swamps previous to the formation of the coal. This "bright" 

 coal retains its original woody structure, although often somewhat 

 distorted. 



The "dull" coal consists of numerous small layers or chips of 

 "bright" coal embedded in a dull matrix, the attritus. These 

 small chips of anthraxylon are derived from the chips, splinters, 

 small stems and branches, twigs, roots, etc. Possibly part of the 

 large woody chunks slightly disintegrated, due to the incipient 

 decay previous to the formation of the coal, and thus provided 

 some of the small layers of "bright" coal. No bark entered into 

 the formation of the small layers of anthraxylon. 



The dull matrix or attritus, in which the small layers of "bright " 

 coal are embedded in the "dull" coal, was derived from the follow- 

 ing sources: 



a) The waxy cuticle covering of the leaves. This is an 

 extremely resistant substance and remains in the coal in narrow, 

 yellowish, semi-transparent bands of varying lengths. 



h) Spore-exines. These vary from o.oi mm. to 3 mm. in cross- 

 section. 



c) Pollen exines. 



d) Resinous matter. This is the original resinous substance of 

 plants. 



e) Small particles of resinous and woody matter from a highly 

 carbonized state down to a Uttle carbonized state. 



/) Small rodlets or needles. These are possibly the petrified 

 or semi-petrified gum or mucilage canals that pervaded the cortex 

 of some Paleozoic plants. On burning, they leave a white quartz 

 skeleton. 



g) Small amounts of gums, pectins, and corks. 



The tannins, terpenes, alkaloids, etc., if still present, are 

 absorbed in the coal and do not show up microscopically. 



