Hays, S. (1972). #aConservation and the gospel of efficiency: The progressive conservation movement, 1890-1920. Atheneum.
Lua i Stíl Chicago (17ú heag.)Hays, Samuel. #aConservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890-1920. New York: Atheneum, 1972.
Lua MLA (9ú heag.)Hays, Samuel. #aConservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890-1920. Atheneum, 1972.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.