Goodall, Brian, author
Penguin Books, 1987
Buku Referensi
edited by R.J. Johnston, Derek Gregory, Geraldine Pratt, Michael Watts
Blackwell Publishing, 2000
Buku Referensi
Lock, C. B. Muriel, author
Clive Bingley, 1972
Buku Referensi
G & C. Merriam Co., 1949
Buku Referensi
Strahler, Arthur N., author
John Wiley & Sons, 1975
Buku Teks