http://pubs.usgs.gov/sir/2008/5140/pdf/Chapter1.pdf Seeger, Cheryl M., History of Mining in the Southeast Missouri Lead District and Description of Mine Processes, Regulatory Controls, Environmental Effects, and Mine Facilities in the Viburnum Trend Subdistrict in Kleeschulte, M.J., ed., 2008, Hydrologic investigations concerning lead mining issues in southeastern Missouri: U.S. Geological Survey Scientific Investigations Report 2008–5140, Chapter 1