The conditions of appointment of the emirs are fully laid down in the terms accepted at Sokoto on the close of the Sokoto-Kano campaign of 1903.
The best known are Koroko, Kong and Bona, entrepots for the trade of the middle Niger, and Bontuku, on the caravan route to Sokoto and the meeting-place of the merchants from Kong and Timbuktu engaged in the kola-nut trade with Ashanti and the Gold Coast.
Tributaries of the Niger traverse the western portion of the country, the most noteworthy being the Gulbin Kebbi or Sokoto river and the Kaduna, which flows through a valley not more than 500 ft.
Limestones, with fossils indicating a Tertiary age, have been found near Sokoto.
Sokoto is the religious and political centre of the Fula.