416 NORTH-WEST AFRICA. expedition of RoUlfs and his associates, who after vainly attempting to perform the first stage of this route from the Dukhul to the Kufra oasis, were comi)elled to stop short and turn northwards bt^twoon the parallel lines of dunes leading to the Siwah oasis. Even the coast of the Sahara between Capes Bojador and Blanco is <.'ne of the least known on the African seaboard, although now annexed to the possessions of a European power. The few meshes of the network traversed by explorers occupy altogether an extend of little over 200,000 square miles. Consequently when we speak of the Sahara, we cannot exclaim with Columbus, " How small is the earth ! " While elsewhere the world grows less, subdued by steam ; while highways are everywhere being constructed and the transport service accelerated, the Sahara remains as difficult of access, as formidable as ever. If the ocean links opposing continents, the desert almost completely separates the neighbouring lands. North and south of the int<^rvening sands, the animal and vegetable kingdoms differ spetifically, and the races of mankind present the sharpest contrasts in their origin, appearance and usages. On the Mediterranean seaboard, as in Europe, the populations have been fre([uently renewed by great waves of migration : Vandals have come from the west after making the circuit of a continent ; Arabs have penetratetl from the east after skirting the shores of the Inland Sea; but across the Sahara from north to south there have been no great movements of population, nor even any conquests by a single military expedition. Here the modifications of type, insti- tutions, and customs have been effected by a slower process of penetration between the northern and southern borderlands. The slaves imported from Sudan have modified the Berber type in ^lauritania, giving rise to the Haratins of the Marocco oases, the Atryas of Twat and Ghadames, the Ruaghas of Algeria. The Arab traders and ijiissionaries have in their turn changed the religion and government of the Sudanese populations. Physical Aspect. The Sahara is not a dried- up marine basin, as was supposed by geologists before the nature of its soil and the inequalities of its relief were' as well understood as they now are. Even the low-l^-ing tracts stretching south of the French possessions, where some of the depressions are actually below the Mediterranean level, have certainly been dry land throughout the Quaternary epoch. Beyond this Berber .H(>ction of the desert no remains of marine origin have anywhere been found. The chalk and sjuidstone formations, the granites, gneiss, porphyries, and bosalte cropj)ing out on its rugged surface show no traces except of weathering by the action of sun, wind, and rains. Throughout its whole extent the Sahara is a continental region, presenting certain marked contrasts in its physical aspect, and containing considerable tracts to which the term desert can scarcely be properh' opplied. Like the other parts of Africa, the Sahara has its highlands, its valleys, and running waters, although n^ainly consisting of vast uniform plateaux, stony wastes, and long ranges of dunes rolling away beyond the horizon, like the billows of a shoreless sea. Here is the
