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Coalified rod-like structures of plant origin have been discovered in fusain bands within bituminous coal beds of the Appalachian and Illinois basins. The rods have been found in the Allegheny, Conemaugh, and Monongahela Formations and Dunkard Group of southwestern Pennsylvania and central and northern West Virginia in coal beds ranging from the upper Freeport coal (uppermost part of the Allegheny) to the Washington coal (lower part of the Dunkard). In the Illinois basin, similar structures are found in the Springfield (No. 5) coal bed of Indiana and in the correlative No. 9 coal bed of western Kentucky in the Carbondale Formation. In 1914 Charles David White discovered similar oriented and disoriented rods in fusain partings in the No. 2 (Colchester) coal bed of Colchest r and Exeter in western Illinois at the base of the Carbondale Formation. In the Illinois basin, the needle-like bodies are associated with coalified wood, cuticles, seed coats, and megaspores.
Under the scanning electron microscope, some of the needle-like structures found in West Virginia are non-cellular and appear to be the remains of resin. Others are woody, cellular in cross section, and have cell walls with pits or pores 1 to 2 µ in diameter in longitudinal section. In polished cross sections of coal, the cellular rods would be described petrographically as sclerotinites. These rods have the appearance of minute match sticks in longitudinal section.
The preliminary work on the biostratigraphic distribution of the rods in coals indicates that they range from Middle to Late Pennsylvanian or younger in age. The association of the rods and highly resistant megaspores, seed coats, cuticles, and coalified wood in fusain bands indicates that they were separated from woody tissue during a period of oxidation of surficial plant matter or peat. Cordaites (a gymnosperm) and tree ferns, which are commonly associated in the partings of the coals, are probable sources of the resin rods.
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