Debenham, Frank, author
Reader's Digest Association, 1979
Buku Referensi
Lye, Keith, author
The Royal Geographical Society, 2000
Buku Referensi
Kidron, Michael, author
Simon & Schuster, 1984
Buku Teks
Pergamon Press, 1968
Buku Referensi
edited by B.M. Willet
George Philip and Son, 1981
Buku Referensi