McIver, J.R., and John Ferguson. “Kimberlitic, Melilititic, Trachytic and Carbonatitic Eruptives at Saltpetre Kop, Sutherland, South Africa”. International Kimberlite Conference: Extended Abstracts, vol. 2, no. 1, Sept. 1977, pp. 212-4, doi:10.29173/ikc995.