Ojha, Ishwer C.
Beacon Press, 1971
Buku Teks
Barghoorn, Frederick C.
Princeton University Press, 1960
Buku Teks
Wesson, Robert G
Houghton mifflin, 1977
Buku Teks
Wesson, Robert G., author
Houghton Miffiln, 1977
Buku Teks
Hansen, Allen C
Praeger, 1984
Buku Teks