Barghoorn, Frederick C.
Princeton University Press, 1960
Buku Teks
Kull, Steven, author
Westview Press, 1992
Buku Teks
Schapiro, Leonard editor
Fredrick A. Praeger, 1963
Buku Teks
Dallin, David J., author
Yale University Press, 1942
Buku Teks
McWhinney, Edward, author
A.W. Sythoff, 1964
Buku Teks