edited by David R. Patrick
Van Nostrand Reinhold, 1994
Buku Referensi
edited by Albert Parker
McGraw-Hill, 1978
Buku Referensi
Paul L. Magill, Francis R. Holden, Charles Ackley, editor; Frederick G. Sawyer, editorial consultant
McGraw-Hill, 1956
Buku Referensi
Davenport, S.J.
Washington, DC: United States Department of the Interior, 1954
Buku Teks
Freeman, Harry M., author
McGraw-Hill, 1971
Buku Referensi