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.
The Central Sahara with these three groups of mountains differs materially from the Eastern Sahara. Although our data for the latter are more limited by lack of knowledge, the structure of the surface immediately west of the Nile Valley appears characteristically to be a series of closed basins. The area is covered with depressions into which insignificant channels flow, and from which there appear to be no outlets. Compared with the river systems of the west, the stream beds are small and ill-defined. One valley of some magnitude, the Bahr Bela Ma which Rohlfs tried to find on his famous journeys in the Libyan desert, has been identified either as a dry channel of the Nile running roughly parallel to it, or alternatively as a valley which starts from N.E. Tibesti and terminates near or in the Wadi Natrun depression just west of the Nile and level with the apex of the Delta. The upper part which drains Tibesti has been called the W. Fardi; elsewhere it is the W. Fareg; the shallow depression crossed by Hassanein Bey on his journey from Jalo to Kufra seems to be part of this system. Examples of closed basins separated from one another by steppe or desert are the oases of Kufra, the Jaghbub-Siwa, Jalo and Lake Chad depressions. In these areas cultivation is frequently intense; salt and fresh water are abundant; and the vegetation sometimes develops luxuriantly into veritable forests of date palms such as exist at Kufra. Between these hollows the intervening Libyan desert is probably the largest and most sterile area of its sort in the world.
The Western Sahara, on the other hand, is essentially an area of well-defined river systems with watersheds and dry beds fashioned on a vast scale. The valleys which extend from the mountains of Ahaggar and the Fezzan to the present River Niger have corresponding channels on the other side of the water-parting running through Southern Algeria or Tunisia towards the Mediterranean. There are good reasons for believing that the original course of the Niger terminated in a swamp or marsh north of Timbuctoo, probably the same collecting basin as that west of Ahaggar into which certain rivers from the Atlas also used to flow. The lower Niger from the eastern side of the great bend where the river now turns south-east and south drained the Central Sahara by a great channel which had its head-waters in Ahaggar and the Fezzan, and ran west of Air.
These Saharan rivers have not contained perennial surface water for long ages. In places they have been covered by more recent sand-dune formations of great extension, but they date from the present geological period. Associated with the desiccation of these valleys is the characteristic of extreme dryness which is one of the few features more or less in accord with popular conceptions of the Sahara. The barrenness of the Sahara is less due to the inherent sterility of the ground than to climatic conditions; desiccation has been intensified in the course of centuries by the purely mechanical processes attendant upon an extremely continental climate and excessively high day temperatures. The latter combined with the extraordinary dryness of the air have contributed to the decay of vegetable, and consequently of animal, life wherever man has not been sufficiently powerful, in numbers or energy, to stay the process. Sterility and desiccation are interacting causes and effects. There is no reason to believe that any sudden change of climate has taken place in the Sahara since the neolithic period, or that it is very much drier now than two thousand years ago. Maximum and minimum temperatures, both average and absolute, have a very wide range seasonally and within the period of twenty-four hours. Temperatures of over 100° F. in the shade are common at all seasons of the year during the day: the thermometer frequently falls to freezing point at night during the winter. Ice is not unknown in the mountains of Tibesti, Air and Ahaggar. The rainfall is irregular except within the belt of summer rains which are so characteristic of Equatorial Africa. In Tibesti the cycle of good rains seems to recur once in thirteen years: in many years both here and elsewhere in the Sahara no rain falls at all. But with these adverse climatic conditions the surprising fact remains, not that the Sahara is so barren, but that it is so relatively well-favoured and capable of supporting different races of people in such comparatively large numbers.[2]
The Air mountains, like the Desert steppes, are only sparsely inhabited. The hill-sides are too wind-swept and rocky to support forests or pastures of any value. Many of the valleys are capable of being cultivated, but in practice are only gardened here and there. In certain districts there are groves of date palms which have been imported from the north. Air is in reality a great Saharan oasis divided from the Equatorial belt by a zone of desert and steppe. It differs from the south in its flora and general conditions, though by its position within the belt of tropical summer rains it belongs climatically to the Sudan.
TRADE ROADS
| F. R. del. | Emery Walker Ltd. sc. |
The oases of the desert, like the Sahara generally, have been the subject of much popular misconception. The origin of the word “oasis,” which has reached us in its present form through the classics, may perhaps be found in ancient Egyptian. It seems to be connected with the name of the Wawat People of the West referred to in the Harris Papyrus,[3] and occurs in the names of Wau el Kebir and Wau el Seghir or el Namus, which are oases in the Eastern Fezzan.[4] The term El Wahat,[5] given to one or several of the oases west of the Nile Valley, contains the same root. An oasis is not necessarily a patch of ground with two or three palm trees and a well in the desert. It is simply an indefinite area of fertility in a barren land; it may or may not happen to have a well. There are oases in Southern Algeria and the Fezzan with hundreds of thousands of palm trees, containing many villages and a permanent population. There are others where the pasture is good but where there is neither population nor water. “Oasis” is a term with no strict denotation, it connotes attributes which render animal life possible.
In this sense Air, as a whole, is an oasis situated on a great caravan road from the Mediterranean to Central Africa. The mountains so lie in respect of the desert to the north and to the south that caravan journeys may be broken in their valleys, and camels can stay to recuperate. The mountains mark a stage on the road, the importance of which it is difficult to over-estimate. In the history of North Africa, the principal routes across the Sahara from the Mediterranean to the Sudan have seemingly not changed at all. Since the earliest times they have followed the shortest tracks from north to south whenever there was sufficient water. If the Nile Valley and the routes in the desert adjacent thereto are left out of account as being suorum generum, there are four main caravan roads across North Africa from north to south. The easternmost runs from Cyrenaica by Kufra to Wadai and Tibesti; only within the last century has it been rendered practicable for caravans by the provision of wells along the southern part, which was opened to heavy traffic by the Senussiya sect. The two central routes run respectively from Tripolitania by the Fezzan, Murzuk and Kawar to Lake Chad, and by Ghadames, Ghat and Air to the Central Sudan. The western route runs from Algeria and Morocco across the desert to Timbuctoo. In addition there is the Moroccan road, which roughly follows the curve of the coast to the Western Sudan and Senegal. Of all these the best known in modern times,[6] and culturally perhaps the most important, has been the Air road. It is noteworthy that all three central routes have been or are within the control of the Tuareg race. As the Tuareg were the caravan drivers of the Central Sahara, so were they also responsible for bringing a certain degree of civilisation from the Mediterranean to Equatorial Africa. That has been their greatest rôle in history.