Chocolate IslandsIn Chocolate Islands: Cocoa, Slavery, and Colonial Africa, Catherine Higgs traces the early twentieth century journey of the Englishman Joseph Burtt to the Portuguese colony of So Tom and Prncipethe chocolate islandsthrough Angola and Mozambique, and finally to British Southern Africa. Burtt had been hired by the chocolate firm Cadbury Brothers Limited to determine if the cocoa it was buying from the islands had been harvested by slave laborers