Lye, Keith
The Royal Geographical Society, 2000
Buku Referensi
Debenham, Frank
Reader's Digest Association, 1979
Buku Referensi
Pergamon Press, 1968
Buku Referensi
edited by B.M. Willet
George Philip and Son, 1981
Buku Referensi
Garden City Books, [date of publication not identified]
Buku Referensi