Makulo La vie de Disasi Makulo, 1982 leaf 36 (Grenfell, George, missionary and explorer, b. England 8/2/1849, d. Basoko 7/1/1906)
Tooley's Dictionary of Mapmakers, 2001 (Grenfell, Reverend George (1849-1906). Cornish missionary in Africa. Surveys of the rivers of the Cameroons, 1874; manuscript maps of the Congo, from 1880; surveys of the Congo River, 1884-1889 used in Map of the Congo River between Leopoldville and Stanley Falls, Royal Geographic Society 1902)