If an original source is unavailable, and "quoted in" must be resorted to, mention the original author and date in the text, and cite the secondry source in the reference list entry. The text citation would include the words "quoted in." (p. 808)
In Louis Zukofsky's "Sincerity and Objectification," from the February 1931 issue of Poetry magazine (quoted in Costello 1981)....
Costello, Bonnie. 1981. Marianne Moore: Imaginary Possessions.
Cam bridge, MA: Harvard University Press.
Notes and Bibliography
If an original source is unavailable, both the original and the secondary source must be listed.
1. Louis Zukofsky, "Sincerity and Objectification," Poetry 37 (February 1931): 269, quoted in Bonnie Costello, Marianne Moore: Imaginary Possessions (Cambridge, MA: Harvard University PRess, 1981), 78.
Costello, Bonnie. Marianne Moore, Imaginary Possessions.
Cambridge, MA: Harvard University Press, 1981.