242 THE EXPLORATION OF THE NIGER Wadalen— Chief Niugi.

Cheibatan— Chief Rafiek. LOGOMATEN— Chief Bokar Wandieidu.

Eratafan— Chief Yoba. Ibendasan. Ahiananurde— Chief Amadida. Tabotan— Chief Muley.

Subject to each of these last-named tribes are imrads but I only know the name of one of their tribes, that of the Ekono, vassals of the Wadalen.

In addition to their predatory excursions the Tuaregs on the right and left bank of the Niger make two annual migrations, the time of which is generally the same.

During the dry season, from December to May, the higher districts are sterile and dry, the ponds and wells empty of water. Then the Tuaregs move down to the river-banks and their flocks and herds graze on the coarse weeds which line them. To avoid the sickness amongst the camels which results from eating damp food, and to which I alluded in speaking of Timbuktu, they generally leave them a little further inland. It is at this time that the negroes pay their tribute of maize and tobacco, and it is also during this same season that warlike expeditions are generally undertaken.

For the rest of the year the rain pours down in torrents in the riverside districts, and although its fall is not so constant or so heavy in the higher lands, they too are fertilized by the filling up of the ponds and the wells, many of which even overflow.

Then the nomad tribes go back again to their old haunts, and settle down for the winter in their camps about the wdies, resembling those of Algeria, which begin near Gao.

These wdies are such very characteristic features of Central Africa, that a description of one of them may be useful. The word wAdy means the channel of a watercourse which is dry except in the rainy season, but there is water in the upper portion of that of Gao in every season.