APPENDIX I. ON THE PHYSICAL GEOGRAPHY OF THE SAHARA, OUR ordinary application of the term "Sahara" for the great northern desert of Africa is not strictly accurate; and in these notes I have restricted its use to that portion of the country to which the natives apply it. They divide Africa north of the line into three portions-the Tell, the Sahara, and the Desert: the Tell being the corn-growing country from the coast to the Atlas; the Sahara the sandy pasture-land, where flocks and herds roam, from the Atlas through the Hauts Plateaux or Steppes to the region where all regular supply of water fails; and the Desert, the region which extends thence almost to the watershed of the Niger -arid, salt, affording no sustenance to cattle or sheep, but where the camel snatches a scanty subsistence, and which is, excepting in its rare oases, equally inhospitable to man. The physical and geological characteristics of these regions vary considerably; but they are all comprehended by the Bedouin under the term " Mogreb," or land towards the sunset, of which the eastern limit is the Gulf of Cabes, and the western the Atlantic. If we cast our eyes on the map of Africa, we shall see no portion of the globe apparently so compact-so selfcontained. A peninsula, attached to Asia alone by a narrow isthmus, Africa exhibits no islands, like those which encircle Europe, struggling, as it were, to be freed from the continent. No deep gulfs and bays indent her shores: she stands compact and solid. The geological convulsions which have dislocated Europe have met with an impenetrable barrier in the ridge of the Atlas, which has sternly repelled every encroachment. But we shall find within this self-contained continent very distinct lines of severance in its physical geography. In the first place, the natural history of the Atlas bears scarcely any affinity to that of the rest of the continent; and this distinctiveness may at once be traced to natural physical causes. To the naturalist North Africa is but an European island, separated, it is true, from Europe by the Mediterranean, but far more effectually isolated from Central Africa by that sea of sand, the Great Desert. The Atlantic isolates it on the west, while a comparatively narrow but most impenetrable desert of ever-shifting sand cuts it off from Tripoli and Egypt, which on their part seem to lean rather on Asia than on Africa. No link attaches Barbary to the rest of the continent; no river supplies an arterial communication; not the most insignificant streamlet forms either a bond of union or a frontier line: the long Atlas chain abruptly terminates in Tunis, and sends not one solitary spur towards Africa; it rather seems by one of its branches to claim kindred with Europe. So far the Arab geographers are accurate in coupling "Mogreb" with Europe instead of Africa. They, too, have the tradition mentioned by Livy, Pliny, and Seneca, that Spain and Morocco were once united-an idea which must so naturally suggest itself to any one who has sailed through the Straits of Gibraltar, that it is needless to imagine that it had any foundation in historic memory. If we might here hazard a conjecture, it would be that the same convulsions and upheavals which at the close of the Tertiary epoch indented the southern coasts of Europe, at the same time drained the ocean which hitherto had rolled over the plains of the Sahara, and submerged the low-lying lands which probably united the Canaries and Madeira to the main land. The natural history of these islands is so essentially European as to point to an identical centre of creation. We may then imagine that towards the close of the later geological epoch Barbary was a vast peninsula, linked to Europe by Gibraltar, and washed on the south by the ocean of the Sahara, on the north by that inland lake which is now the Mediterranean. But when, leaving the southern slopes of the Atlas, we enter upon the Sahara, the physical and geological characteristics are changed at once. Upon the surface of the secondary and some of the tertiary deposits we stumble over beds of rounded pebble and large gravel, besides the extraordinary mountains of pure rock-salt which in various places rise suddenly from the limestone. To picture the Sahara, imagine what the north-east portion of England would be if completely drained of its streams and denuded of its vegetation: wooded dells transformed into rocky naked nullahs, and tillage plains covered with a soil pulverized by the combined action of heat, wind, and attrition. With all its monotony, the Desert has its varieties. One day you laboriously pick your steps among bare rocks, now sharp enough to wound the tough sole of your camel, now so slippery that the Arab horse can scarce make good his footing. Another day you plunge for miles knee-deep in loose suffocating sand-drifts, ever changing and threatening to bury you when you halt. Sometimes a hard pebbly surface permits a canter for hours over the level plain amidst dwarf leafless dust-coloured shrubs. Perhaps, on surmounting a ridge, the mirage of a vast lake glittering in the sunshine excites both the horse and his rider. On, on, gallops the wiry little steed over sand hard and crisp, and coated with a delicate crust of saltpetre, the deposit of the water which at rare intervals has accumulated there and formed the Chotts and Sebkhas of the Desert. Occasionally the traveller is gladdened and refreshed by pitching his camp in a dayat, or reposing for a few nights under the palm-trees of an oasis. The Sahara may be divided, as to its physical geography, into three distinct portions-the district of the Hauts Plateaux, that of the Dayats, and the southern level district of the Oases. The northern portion or steppes may be considered as commencing at the foot of the Atlas range, |