British Southern Africa. Various Philatelic literature and auction catalogues, including Handbook of Postmarks of South West Africa by R.F. Putzel; The Postmarks of The Orange Free State and Orange River Colony 1868 to 1910 by A G M Batten; More About The Postmarks of The Orange Free State and Orange River Colony 1868 - 1910 by A G M Batten plus Appendices; The Special Commemorative Postmarks, Cachets and Covers of South Africa 1892 to 1975 by H O Reisener; The Cancellations of The Rhodesias and Nyasaland by H C Dann; The Postal History of Nyasaland by E B Proud; The Cancellations of Kenya 1890 to 1963 by East African Study Circle