Description
Item Description:Title from title screen (as viewed on Feb. 18, 2009).
Electronic resource.
Physical Description:vii, 65 pages : digital, PDF file.
Format:Mode of access: Internet from the USGS web site. Address as of 5/8/09: http://pubs.usgs.gov/circ/1331/Circ1331.pdf ; current access available via PURL.
Bibliography:Includes bibliographical references (pages 39-45).
ISBN:9781411323254
1411323254