Mode of access: Internet from the USGS web site. Address as of 7/12/04: http://energy.usgs.gov/factsheets/NERSL/nersl.html; current access is available via PURL. Title from title screen (viewed on July 12, 2004). "Nick Zihlman." "August 1994." "Last updated 23-Sept-1997." Series and numbering from the USGS Fact Sheet home page.