Lye, Keith
The Royal Geographical Society, 2000
Buku Referensi
Kidron, Michael
Simon & Schuster, 1984
Buku Teks
Pergamon Press, 1968
Buku Referensi
edited by B.M. Willet
George Philip and Son, 1981
Buku Referensi
edited by Andrew Heritage
Dorling Kindersley, 2000
Buku Referensi