To the general public the name Sahara denotes “Desert,” and the latter connotes sand and thirst and camels and picturesque men and veiled women. The Sahara in reality is very different. Its surface and races are varied. Almost every type of physical feature, except permanent glaciation, can be found. The greater part is capable of supporting animal and vegetable life in some degree. Absolute desert where no living thing can exist does not on the whole form a very large proportion of the surface. It has become usual nowadays to differentiate between the cultivated or cultivable areas, the steppe desert and the true desert. The latter alone is devoid of organic life, and is the exception rather than the rule. The mountain groups of the Sahara fall, as an intermediate category, between the cultivated and the desert lands. Generally speaking, animal and vegetable life exist in the valleys, where some tillage is often possible. The density of population, however, is never comparable with that of the cultivated districts, which, except where they fringe the coast, are usually included in the term “oases.” The mountain groups of the Sahara are numerous and comparatively high. There are summits in the more important massifs exceeding 10,000 feet above the sea. The three most important groups in the Central Sahara are the Tibesti, Air and Ahaggar mountains. In such a generalisation, reference to the Atlas and other mountain masses in Algeria and Morocco may be omitted, since they do not properly speaking belong to the Sahara. The three Saharan massifs are probably of volcanic origin. They have only become known in recent years, and even now have not been fully explored. This is especially the case in regard to Tibesti, an area believed to be orographically connected with Air by the almost unknown plateau of the Southern Fezzan.