Tweedie, Alan D., author
Longmans, 1965
Buku Teks
Crawford, R. M.
Hutchinson's University Library, 1955
Buku Teks
Crawford, R.M., author
Hutchinson University Library, 1952.
Buku Teks
De Blij, Harm J., author
John Wiley & Sons, 2005
Buku Teks
De Blij, Harm J., author
John Wiley & Sons, 1971
Buku Teks