Dyfyniad APA

Harland, W. B., & Armstrong, R. L. (1990). A geologic time scale 1989 (Rev. ed.). Cambridge University Press.

Dyfyniad Arddull Chicago

Harland, W. Brian, and Richard L. Armstrong. A Geologic Time Scale 1989. Rev. ed. Cambridge ; New York: Cambridge University Press, 1990.

Dyfyniad MLA

Harland, W. Brian, and Richard L. Armstrong. A Geologic Time Scale 1989. Rev. ed. Cambridge University Press, 1990.

Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.