Bell, Charles. “Notes on South African Bored Stones, or Perforated Stone Balls, and a Hafted Stone Axe from South Australia, Presented to the Museum; With Notice of Cave Paintings in South Africa”. Proceedings of the Society of Antiquaries of Scotland, vol. 11, Nov. 1875, pp. 140-5, doi:10.9750/PSAS.011.140.145.