edited by David R. Patrick
Van Nostrand Reinhold, 1994
Buku Referensi
edited by Albert Parker
McGraw-Hill, 1978
Buku Referensi
Davenport, S.J.
Washington, DC: United States Department of the Interior, 1954
Buku Teks
Heihnson, Robert Jennings
Prentice-Hall, 1999
Buku Teks
Cooper, C. David
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Buku Teks