Bush, H. K. (2007). Mark Twain and the spiritual crisis of his age. University of Alabama Press.
Lua i Stíl Chicago (17ú heag.)Bush, Harold K. Mark Twain and the Spiritual Crisis of His Age. Tuscaloosa: University of Alabama Press, 2007.
Lua MLA (9ú heag.)Bush, Harold K. Mark Twain and the Spiritual Crisis of His Age. University of Alabama Press, 2007.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.