(en) Stephen Adrian Craven, « Cango Cave, Oudtshoorn District of the Cape Province, South Africa: An Assessment of Its Development and Management 1780–1992 », Thèse de doctorat, Cape Town, South Africa: University of Cape Town, (OCLC890424645, lire en ligne)
web.archive.org
(en) Pat R. Irwin, EEASA in a Changing World: An Historical Review at 25 Years, Howick, South Africa: Environmental Education Association of Southern Africa, (ISBN978-0-86810-439-3, lire en ligne)
worldcat.org
(en) R. K. Muir, « John McGregor Niven (1921–1991) », South Africa: Natal Society Foundation, , p. 68–71 (OCLC5878048709, lire en ligne)
(en) Stephen Adrian Craven, « Cango Cave, Oudtshoorn District of the Cape Province, South Africa: An Assessment of Its Development and Management 1780–1992 », Thèse de doctorat, Cape Town, South Africa: University of Cape Town, (OCLC890424645, lire en ligne)