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ATLAS
MOUNTAINS
circulation. In the North Atlantic this region is covered by enormous banks of gulf-weed (Sargassum bucciferum), hence the name Sargasso Sea. The Sargasso Sea is bounded, roughly, by the lines of 20°-35° N. lat. and 40°-75° W. long. The sub-surface circulation in the Atlantic may be regarded as consisting of two parts. Where water is banked up against the land, as by the equatorial and Gulf Stream drift currents, it appears to penetrate to very considerable depths; the escaping stream currents are at first of great vertical thickness, and part of the water at their sources has a downward movement. In the case of the Gulf Stream, which is not much impeded by the land, this descending motion is relatively slight, being perhaps largely due to the greater specific gravity of the water; it ceases to be perceptible beyond about 500 fathoms. On the European-African side the descending movement is more marked, because the coast-line is much more irregular, and the northward current is deflected against it by the earth’s rotation; here the movement is traceable to at least 1000 fathoms. The northward movement of water across the Norwegian Sea extends down from the surface to the Iceland-Shetland ridge, where it is sharply cut off; the lower levels of the Norwegian Sea are filled with ice-cold Arctic water, close down to the ridge. The south-moving currents originating from melting ice are probably quite shallow. The second part of the circulation in the depth is the slow “creep” of water of very low temperature along the bottom. The North Atlantic being altogether cut off from the Arctic regions, and the vertical circulation being active, this movement is practically non-existent; but in the South Atlantic, where communication with the Southern Ocean is perfectly open, Antarctic water can be traced to the equator, and even beyond. The tides of the Atlantic Ocean are of great complexity. The tidal wave of the Southern Ocean, which sweeps uninterruptedly round the globe from east to west, generates a secondary wave between Africa and South America, which travels north at a rate dependent only on the depth of the ocean. With this “ free ” wave is combined a “forced wave,” generated, by the direct action of the sun and moon, within the Atlantic area itself. Nothing is known about the relative importance of these two waves. (h. n. d.) Atlas Mountains.—Since the exploration of the western section by Hooker and Ball in 1878, this range has been visited and even crossed at more than one point by later travellers. Oscar Lenz, who surveyed a considerable part of the Great Atlas north of Tarudant, and determined a pass south of Ihr in the Little Atlas in 1879-80, and penetrated thence across the Sahara southwards to Timbuktu, was followed in 1883-84 by Ch. de Foucauld, whose extensive itineraries include many districts that had never before been visited by any Europeans. Such were parts of the first and middle ranges crossed once; three routes over the Great Atlas, which was moreover traversed along both flanks nearly for its whole length; and six journeys across the Little Atlas, with a general survey of the foot of this range and several passages over the Jebel-Bani. Then came the late Joseph Thomson, who explored some of the central parts, but broke little new ground, and failed to cross the main range (1888); H. M. P. de la Martiniere, who increased our knowledge of the uplands in the province of Fez (1890-91); and lastly, Walter B. Harris, who explored some of the southern slopes and crossed the Little Atlas during his expedition to the Tafilet oasis (1894). Thanks to these expeditions, and especially to De Foucauld’s careful surveys, we now possess a somewhat
clear idea of the hitherto imperfectly known Atlas system in its more important western (Moroccan) section, which bears the comprehensive Berber name of Adrar n’Deren, the “ Deren Mountains.” Here it forms not two or three chains, as hitherto supposed, but as many as five distinct ranges, all varying in length and height, but disposed parallel to one another in the normal direction from southwest to north-east, with a slight curvature towards theSahara. Generally speaking, the northern more or less convex slopes, being exposed to the moist Atlantic winds, are in many places well wooded, while the southern flanks, which intercept the dry Saharan winds, are mainly destitute of vegetation. The main range, commonly known as the Great Atlas, occupies a central position in the system, and is by far the longest and loftiest chain, terminating, not in a plateau as often asserted, but in a sharply outlined crest, and culminating between the Bibawan Pass and the Jebel Aishin. The fall towards the Dahra district at the north-east end is gradual and continuous, but precipitous at the opposite extremity facing the Atlantic between Agadir and Mogador. At several points the crest has been deeply eroded by old glaciers and running waters, and thus have been formed a number of passes, which, however, are little utilized for peaceful intercourse, the approaches on both slopes being mostly held and blocked rather than kept open by mutually hostile Berber tribes. The Aishin section, culminating in a peak nearly 15,000 feet high, maintains a mean altitude of 11,600 feet, and from this great mass of schists and sandstones a number of secondary ridges radiate in all directions, forming divides between the Um-er-Rebia, the Sebu, the Muluya, the Ghir, and the Draa, which flow respectively to the west, north-west, north-east, south-east and south. Eastwards the Aishin terminates abruptly in the steep Jebel-Terne'ft cliffs, which rise some 6000 feet above the surrounding plains. For a distance of 100 miles it nowhere presents any passes accessible to caravans ; but south-westwards some gaps in the range afford communication between the Um-er-Rebia and the Draa basins. In the same direction the Aishin is continued by a not yet named crest, which appears to maintain the same mean altitude of considerably over 11,000 feet, and it is this south-western extension of the Moroccan system which gives it greater average height than the European Alps, although dominated by less elevated peaks. Yet a few summits in the extreme south-west still exceed 11,000 feet in the neighbourhood of Cape Ghir. Besides huge masses of old schists and sandstones, geologists have discovered extensive limestone, marble, diorite, basalt, and porphyry formations, while granite prevails on the southern slopes of the Aishin range. The presence of enormous glaciers in the Ice Age is attested by the moraines at the Atlantic end, and by other indications farther east. The best known passes are : (1) The BibawAn in the upper Wed-Sus basin (4150 feet according to Lenz) ; (2) the Tizi, i.e., the “Pass” in a pre-eminent sense, giving access from Marakesh to Tarudant, rugged and difficult, but low, and utilized by Lempriere, Jackson, Lenz, and other travellers; (3) Tizi n’Tameffut, leading down to the Draa valley; (4) Tizi n’Glawi (7600 feet, Foucauld); (5) Tizi n’Telremt (7250 feet, Foucauld), leading down to the Wed-Ghir. The Middle Atlas, skirting the north flank of the Great Atlas at some distance inland, is not visible from the coast, and is still but little known; but seems to run from the region north of Demnat The to the Dahra district beyond Debdon, presents f^ages.^ a somewhat regular snowy crest between the Um-er-Rebia and the Wed el-Abid valleys, and is crossed
