1. Irwin J. , ‘An Emirate of the Niger Bend: A Political History of Liptako in the Nineteenth Century’, Ph.D. thesis, unpublished, University of Wisconsin, 1973, 18–19.
2. Ferguson Douglas Edwin , ‘Nineteenth-Century Hausaland, being a description by Imam Imoru of the Land, Economy, and Society of his People’, Ph.D. thesis, unpublished, UCLA, 1973
3. Lovejoy , ‘Salt Industry’
4. Abubakar Saad , ‘A Survey of the Economy of the Eastern Emirates of the Sokoto Caliphate in the Nineteenth Century’, unpublished paper presented at the Sokoto Seminar, Departments of History, Ahmadu Bello University and Bayero University College, Sokoto, 1975.