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  1. Geologic investigation of roof and floor strata : longwall demonstration, Old Ben Mine no. 24 : prediction of coal balls in the Herrin coal : final technical report, part 2 /
    By: DeMaris, Philip J.
    Publication info: Champaign, Ill. :Illinois Dept. of Energy and Natural Resources, State Geological Survey Division,1983.
    Contributed by: University of Illinois Urbana Champaign
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