Hunt, Kellogg W.
Houghton Miffiln, 1967
Buku Teks
Ballard, Robert D.
National Geographic Society, 1983
Buku Referensi
edited by Claude T. Bissell
Published in association with Carleton University by University of Toronto Pres, 1957
Buku Teks
Unger, Peter
Oxford University Press , 1996
Buku Teks
editor, Clifton Fadiman
Doubleday, 1990
Buku Teks SO