Harrison, Roy M.
Whitstable Litho, 1982
Buku Teks
Crawford, Martin
Tata McGraw-Hill, 1976
Buku Teks
edited by F.R. Benn and C.A. McAuliffe
Macmillan Press , 1975
Buku Teks
Clark, R.B.
Clarendon Press, 1986
Buku Teks
Davenport, S.J.
Washington, DC: United States Department of the Interior, 1954
Buku Teks