Heard, G. (1935). The source of civilization. Cape.
Lua i Stíl Chicago (17ú heag.)Heard, Gerald. The Source of Civilization. London: Cape, 1935.
Lua MLA (8ú heag.)Heard, Gerald. The Source of Civilization. Cape, 1935.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.