"The National Coal Resource Assessment (NCRA) project by the U.S. Geological Survey is designed to assess U.S. coal with the greatest potential for development in the next 20-30 years"--P. 4.
Includes bibliographical references (pages 47-49).
Also available via Internet from the USGS web site. Address as of 1/28/00: http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-98-0789-a/; current access is available via PURL.