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Footnote

1David White and others, "Contributions to Economic Geology: Short
Papers and Preliminary Reports" (George H. Ashley, The Santo Tomas
Cannel Coal, Webb County, Texas), in Bulletin 691 (Part II, Mineral
Fuels) of the U. S. Geological Survey, pp. 251-270; see also George H.
Ashley, "Cannel Coal in the United States," in Bulletin 659 of the United
States Geological Survey, pp. 121-122.