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Polished column samples representing the Davis, Dekoven, No. 5, and No. 6 seams of southern Illinois were studied megascopically. The lithotypes identified were vitrain, clarain (bright and dull), durain, and fusain. Partings also were determined. Layers on the polished surfaces were identified down to a thickness of 1 mm. On the basis of these data, the seams were divided into petrographically distinctive intervals which were characterized as bright, semibright, semidull, and dull, depending upon the proportions of vitrain and bright clarain present. A comparison of profiles suggested that each seam has its own characteristic pattern and that this pattern has lateral persistence as indicated by the No. 6 seam profiles. A comparison of polished column data with in-situ descriptions for the No. 6 seam was less satisfactory, revealing only general similarities. Maceral contents determined on a number of the megascopically identified layers from two of the columns studied showed wide ranges for some of the lithotypes, particularly bright and dull clarain and durain, even though mean maceral contents increased and decreased according to predictable patterns. Mineral matter appeared to be a major factor in decreasing the luster of some layers resulting in their assignment to durain and dull clarain.
coal, petrography, megascopic description, polished blocks, coal deposits, partings, lithotype, seam profiles, maceral content
Institute of Sedimentary and Petroleum Geology, Geological Survey of Canada, Calgary, Alberta