Note 16 — STEPPES AND DESERTS.

p. 8.—“Like the greater part of the Desert of Sahara, the Llanos are in the torrid zone.”

Significant denominations,—particularly such as refer to the form in relief of the earth’s surface, and which have arisen at a period when there was only very uncertain information respecting the countries in question and their hypsometric relations,—have led to various and long-continued geographical errors. The ancient denomination of the “Greater and Lesser Atlas” (Ptol. Geogr. lib. iii. cap. 1) has exercised the prejudicial influence here alluded to. No doubt the snow-covered western summits of the Atlas in the territory of Morocco may be regarded as the Great Atlas of Ptolemy; but where is the limit of the Little Atlas? Is the division into two Atlas chains, which the conservative tendencies of geographers have preserved for 1700 years, to be still maintained in the territory of Algiers, and even between Tunis and Tlemse? Are we to seek between the coast and the interior for parallel chains constituting a greater and a lesser Atlas? All travellers familiar with geognostical views, who have visited Algeria since it has been taken possession of by the French, contest the meaning conveyed by the generally received nomenclature. Among the parallel chains, that of Jurjura is generally supposed to be the highest of those which have been measured; but the well-informed Fournel, (long Ingenieur en chef des Mines de l’Algérie), affirms that the mountains of Aurès, near Batnah, which were still found covered with snow at the end of March, are higher. Fournel denies the existence of a Little and a Great Atlas, as I do that of a Little and a Great Altai (Asie Centrale, T. i. p. 247–252). There is only one Atlas, formerly called Dyris by the Mauritanians, and this name is to be applied to the “foldings,” (“rides”) or succession of crests which form the division between the waters flowing to the Mediterranean, and those which flow towards the Sahara lowland. The strike or direction of the Eastern Mauritanian portion of the Atlas is from east to west; that of the elevated Atlas of Morocco from north-east to south-west. The latter rises into summits which, according to Renou, (Exploration Scientifique de l’Algérie de 1840 à 1842, publiée par ordre du Gouvernement, Sciences Hist. et Geogr. T. viii. 1846, p. 364 and 373), attain an elevation of 10,700 Fr. (11400 Eng.) feet; exceeding, therefore, the height of Etna. A singularly formed highland of an almost square shape, (Sahab el Marga), bounded on the south by higher elevations, is situated in 33° lat. From thence towards the sea to the west, about a degree south of Mogador, the Atlas declines in height: this south-westernmost part bears the name of Idrar-N-Deren.

The northern Mauritanian boundaries of the widely extended low region of the Sahara, as well as its southern limits towards the fertile Soudan, are still but little known. If we take on a mean estimation the parallels of 16½° and 32½° as the outside limits, we obtain for the Desert, including its Oases, an area of more than 118500 square German geographical miles; or between nine and ten times the area of Germany, and almost three times that of the Mediterranean exclusive of the Black Sea. From the best and most recent intelligence, for which we are indebted to the French Colonel Daumas and MM. Fournel, Renou, and Carette, we learn that the desert of Sahara is composed of several detached basins, and that the number and the population of the fertile Oases is very much greater than had been imagined from the awfully desert character of the route between Insalah and Timbuctoo, and that from Mourzouk in Fezzan, to Bilma, Tirtuma, and Lake Tschad. It is now generally affirmed that the sand covers only the smaller portion of the great lowland. A similar opinion had been previously propounded by the acutely observant Ehrenberg, my Siberian travelling companion, from what he had himself seen (Exploration Scientifique de l’Algérie, Hist. et Geogr. T. ii. p. 332). Of larger wild animals, only gazelles, wild asses, and ostriches are to be met with. “Le lion du désert,” says M. Carette, (Explor. de l’Alg. T. ii. p. 126–129; T. vii. p. 94 and 97), “est un mythe popularisé par les artistes et les poètes. Il n’existe que dans leur imagination. Cet animal ne sort pas de sa montagne où il trouve de quoi se loger, s’abreuver et se nourrir. Quand on parle aux habitans du désert de ces bêtes féroces que les Européens leur donnent pour compagnons, ils repondent avec un imperturbable sang froid, il y a donc chez vous des lions qui boivent de l’air et broutent des feuilles? Chez nous il faut aux lions de l’eau courante et de la chair vive. Aussi des lions ne paraissent dans le Zahara que là où il y a des collines boisées et de l’eau. Nous ne craignons que la vipère (lefa) et d’innombrables essaims de moustiques, ces derniers là où il y a quelque humidité.”

Whereas Dr. Oudney, in the course of the long journey from Tripoli to Lake Tschad, estimated the elevation of the southern Sahara at 1637 English feet, to which German geographers have even ventured to add an additional thousand feet, the Ingenieur Fournel has, by careful barometric measurements based on corresponding observations, made it tolerably probable that a part of the northern desert is below the level of the sea. That portion of the desert which is now called “le Zahara d’Algérie” advances to the chains of hills of Metlili and el-Gaous, where the northernmost of all the Oases,—that of el-Kantara, fruitful in dates,—is situated. This low basin, which touches the parallel of 34° lat., receives the radiant heat of a stratum of chalk, (full of the shells of Inoceramus), inclined at an angle of 65° towards the south (Fournel sur les Gisemens de Muriate de Soude en Algérie, p. 6 in the Annales des Mines, 4me Série, T. ix., 1846, p. 546). “Arrivés a Biscara,” (Biskra), says Fournel, “un horizon indéfini comme celui de la mer se déroulait devant nous.” Between Biscara and Sidi Ocba the ground is only 228 (243 Eng.) feet above the level of the sea. The inclination increases considerably towards the south. In another work, (Asie Centrale, T. ii. p. 320), where I have brought together everything relating to the depression of some portions of continents below the level of the sea, I have already noticed that according to Le Père the “bitter lakes” on the isthmus of Suez, when they have a little water,—and, according to General Andréossy, the Natron lakes of Fayoum,—are also lower than the level of the Mediterranean.

Among other manuscript notices of M. Fournel, I possess a vertical geological profile, which gives all the inflexions and inclinations of the strata, representing a section of the surface the whole way from Philippeville on the coast to the Desert of Sahara, at a spot not far from the Oasis of Biscara. The direction of the line on which the barometric measurements were taken is south 20° west; but the elevations determined are projected, as in my Mexican profiles, on a different plane,—a north-south one. Ascending uninterruptedly from Constantine, at an elevation of 332 toises (2122 Eng. feet), the culminating point is found between Batnah and Tizur, at an elevation of only 560 toises (3580 Eng. feet). In the part of the desert situated between Biscara and Tuggurt, Fournel has had a series of Artesian wells dug with success (Comptes Rendus de l’Acad. des Sciences, t. xx. 1845, p. 170, 882, and 1305). We learn from the old accounts of Shaw, that the inhabitants of the country knew of a subterranean supply of water, and relate fabulous tales of a “sea under the earth (bahr tôht el-erd).” Fresh waters flowing between clay and marl strata of the old cretaceous and other sedimentary deposits, under the action of hydrostatic pressure form gushing fountains when the strata are pierced (Shaw, Voyages dans plusieurs parties de la Berbérie, t. i. p. 169; Rennell, Africa, Append. p. lxxxv). That fresh water in this part of the world should often be found near beds of rock salt, need not surprise geologists acquainted with mines, since Europe offers many analogous phenomena.

The riches of the desert in rock-salt, and the fact of rock-salt having been used in building, have been known since the time of Herodotus. The salt zone of the Sahara (zone salifère du désert), is the southernmost of three zones, stretching across Northern Africa from south-west to north-east, and believed to be connected with the beds or deposits of rock-salt of Sicily and Palestine, described by Friedrich Hoffman and by Robinson. (Fournel, sur les Gisements de Muriate de Soude en Algérie, p. 28–41; Karsten über das Vorkommen des Kochsalzes auf der Oberfläche der Erde, 1846, S. 497, 648, and 741.) The trade in salt with Soudan, and the possibility of cultivating dates in the Oases, formed by depressions caused probably by falls or subsidences of the earth in the gypsum beds of the tertiary cretaceous or keuper promotions, have alike contributed to enliven the Desert, at least to some extent, by human intercourse. The high temperature of the air, which makes the day’s march so oppressive, renders the coldness of the nights, (of which Denham complained so often in the African Desert, and Sir Alexander Burnes in the Asiatic), so much the more striking. Melloni, (Memoria sull’ abassamento di temperatura durante le notti placide e serene, 1847, p. 55), ascribes this cold, produced doubtless by the radiation from the ground, less to the great purity and serenity of the sky, (irrigiamento calorifico per la grande serenità di cielo nell’ immensa e deserta pianura dell’ Africa centrale), than to the profound calm, the nightly absence of all movement in the atmosphere. (Consult also, respecting African meteorology, Aimé in the Exploration de l’Algérie, Physique génerale, T. ii., 1846, p. 147.)

The southern declivity of the Atlas of Morocco sends to the Sahara, in lat. 32°, a river, the Quad-Dra (Wady-Dra), which for the greater part of the year is nearly dry, and which Renou (Explor. de l’Alg. Hist. et Geogr., T. viii. p. 65–78) considers to be a sixth longer than the Rhine. It flows at first from north to south, until, in lat. 29° N. and long. 5° W., it turns almost at right angles to its former course, runs to the west, and, after passing through the great fresh water Lake of Debaid, enters the sea at Cape Nun, in lat. 28° 46′ N. and long. 11° 08′ W. This region, which was so celebrated formerly in the history of the Portuguese discoveries of the 15th century, and was afterwards wrapped in profound geographical obscurity, is now called on the coast “the country of the Sheikh Beirouk,” (a chief independent of the Emperor of Morocco.) It was explored in the months of July and August 1840, by Captain Count Bouet-Villaumez of the French Navy, by order of his government. From the official Reports and Surveys which have been communicated to me in manuscript, it appears evident that the mouth of the Quad-Dra is at present very much stopped up with sand, having an open channel of only about 190 English feet wide. A somewhat more easterly channel in the same mouth is that of the still very little known Saguiel el-Hamra, which comes from the south, and is supposed to have a course of at least 600 geographical miles. One is astonished at the length of these deep, but commonly dry river beds. They are ancient furrows, such as I have seen in the Peruvian desert at the foot of the Cordilleras, between those mountains and the coast of the Pacific. In Bouet’s manuscript “Relation de l’Expédition de la Malouine,” the mountains which rise to the north of Cape Nun are estimated at the great elevation of 2800 metres (9185 English feet).

Cape Nun is usually supposed to have been discovered in 1433, by the Knight Gilianez, acting under the command of the celebrated Infante Henry Duke of Viseo, and founder of the Academy of Sagres, which was presided over by the pilot and cosmographer Mestre Jacomè of Majorca; but the Portulano Mediceo, the work of a Genoese Navigator in 1351, already contains the name of Cavo di Non. The passage round this Cape was then as much dreaded as that of Cape Horn has since been, although it is 23′ north of the parallel of Teneriffe, and could be reached in a few days’ voyage from Cadiz. The Portuguese proverb, “quem passa o Cabo di Num, ou tornarà ou não,” could not deter the Infante, whose heraldic French motto, “talent de bien faire,” expressed his noble, enterprising, and vigorous character. The name of the Cape, in which a play of words on the negative particle has long been supposed, does not appear to me to have had a Portuguese origin. Ptolemy placed on the north-west coast of Africa a river Nuius, in the Latin version Nunii Ostia. Edrisi speaks of a town, Nul, or Wadi Nun, somewhat more to the south, and three days’ journey in the interior: Leo Africanus calls it Belad de Non. Long before the Portuguese squadron of Gilianez, other European navigators had advanced much beyond, or to the southward of, this Cape. The Catalan, Don Jayme Ferrer, in 1346, as we learn from the Atlas Catalan published by Buchon at Paris, had advanced as far as the Gold River, (Rio do Ouro), in lat. 23° 56′; and Normans, at the end of the 14th century, as far as Sierra Leone in lat. 8° 30′. The merit of having been the first to cross the equator on the western coast of Africa belongs, however, like that of so many other memorable achievements, to the Portuguese.