List of sources:
General directory and guide book to the Cape of Good Hope and its dependencies, 1872-1876 (Port Elizabeth Mechanics' Institue).
Gunn, M. & Codd, L.E. Botanical exploration of southern Africa. Cape Town: Balkema, 1981.
Jeppe, Fred. Transvaal book almanac and directory, 1877, p. 51. Reprinted by the State Library, Pretoria, 1976.
Mendelssohn, S. South African bibliography. London, 1910.
National Union Catalogue, pre-1956 imprints. London: Mansell, 1968-1980.
National Automated Archival Information Retrieval System (NAAIRS). http://www.national.archives.gov.za/naairs.htm Documents relating to Greenstock, William / Greenstock, W. / Greenstock, Reverend.
Newbury, Paul. Reverend
William Greenstock. Retrieved from http://archiver.rootsweb.ancestry.com/th/read/SOUTH-AFRICA-EASTERN-CAPE/2005-04/1113672661
on 15 March 2017.
Port Elizabeth directory and guide to the Eastern Province of the Cape of Good Hope, 1872-1876.
South African bibliography to the year 1925. London, Mansell, 1979.