Note 16 — ON STEPPES AND DESERTS.

p. 7—“Like the greater part of the Desert of Sahara, the Llanos lie within the Torrid Zone.”

Significant denominations, particularly such as refer to the form of the earth’s surface, and which arose at a period when there was only very uncertain information respecting different regions and their hypsometric relations, have led to various and long-continued geographical errors. The ancient Ptolemaic denomination of the “Greater and Lesser Atlas”^[DG] has exercised the injurious influence here indicated. There is no doubt that the snow-covered western summits of the Atlas of Morocco may 89be regarded as the Great Atlas of Ptolemy; but where is the limit of the Little Atlas? Are we still to maintain the division into two Atlas chains (which the conservative tendency of geographers has retained for 1700 years) in the territory of Algiers, and even between Tunis and Tlemse? Are we to seek a Greater and a Lesser Atlas between the coast and the parallel chains of the interior? All travellers familiar with geognostic views, who have visited Algeria since it has been in the possession of the French, contest the meaning conveyed by the generally adopted 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 (who was long Ingénieur en chef des Mines de l’Algérie) affirms that the mountain range of Aurès, near Batnah, which even at the end of March was found covered with snow, has a greater elevation. Fournel contests the existence of a Little and a Great Atlas, as I do that of a Little and a Great Altai^[DH]. There is but one Atlas, formerly called Dyris by the Mauritanians, “a name that must be applied to the foldings (rides, suites de crêtes), which form the division between the waters flowing to the Mediterranean and towards the lowland of the Sahara.” The lofty Atlas chain of Morocco inclines from north-east to south-west, and not, like the Eastern Mauritanian portion of the Atlas, from east to west. It rises into summits which, according to Renou, attain an elevation of 11,400 feet, exceeding, therefore, the height of Etna^[DI]. A singularly formed highland, of an almost square shape (Sahab el-Marga), is situated in 33° north lat., and is bounded to the south by high elevations. From thence the Atlas declines in height in a westerly direction towards the sea, about a degree south of Mogador. This south-western portion bears the name of Idrar-N-Deren.

The northern boundaries of the extended low region of the Sahara in Mauritania, as well as its southern limits towards the fertile Sudan, have hitherto been but imperfectly investigated. If we take the parallels of 16½° and 32½° north lat. as the outer limits, we obtain for the Desert, including its oases, an area of more than 1,896,000 square miles; 90or between nine and ten times the extent of Germany, and almost three times that of the Mediterranean, exclusive of the Black Sea. The best and most recent intelligence, for which we are indebted to the French observers, Colonel Daumas, and MM. Fournel, Renou, and Carette, shows us 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 country between Insalah and Timbuctoo, and the road 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 lowlands. A similar opinion had been previously advanced by my Siberian travelling companion, the acute observer Ehrenberg, from what he had himself seen^[DJ]. Of larger wild animals, only gazelles, wild asses, and ostriches are to be met with.

“That lions exist in the desert,” says M. Carette, “is a myth popularised by the dreams of artists and poets, and has no foundation but in their imagination. This animal does not quit the mountains where it finds shelter, food, and drink. When the traveller questions the natives concerning these wild beasts, which Europeans suppose to be their companions in the desert, they reply, with imperturbable sang froid, ‘Have you, then, lions in your country which can drink air and eat leaves? With us lions require running water and living flesh; and therefore they only appear where there are wooded hills and water. We fear only the viper (lefa), and, in humid spots, the innumerable swarms of mosquitoes which abound there.^[DK]’”

While Dr. Oudney, in his long journey from Tripoli to Lake Tschad, estimated the elevation of the Southern Sahara at 1637 feet, and German geographers even ventured to add an additional thousand feet, Fournel, the engineer, has, by careful barometric measurements, based on corresponding observations, made it tolerably probable that a part of the northern desert is below the sea’s level. The portion of the desert which is now called “Le Zahara d’Algérie,” advances to the chains of hills of Metlili and el-Gaous, where lies the most northern of all the Oases, el-Kantara, fruitful in dates. This low basin, which reaches the parallel of 34° lat., receives 91the radiant heat of a stratum of chalk, inclined at an angle of 65° towards the south, and which is full of the shells of Inoceramus^[DL]. “Arrived at Biscara (Biskra),” says Fournel, “an indefinite horizon, like that of the sea, lay spread before us.” Between Biscara and Sidi Ocba the land is only 243 feet above the sea’s level. The inclination increases considerably towards the south. In another work^[DM], where I have brought together all the points that refer 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 (lacs amers) on the isthmus of Suez, when they have but 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 geognostic vertical profile, with all the inflexions and inclinations of the strata, representing the surface the whole way from the coast near Philippeville to a spot near the Oasis of Biscara in the Desert of Sahara. The direction of the line on which the barometric measurements were taken is south 20° west; but the points of elevation determined are projected, as in my Mexican profiles, on a different plane, one from N. to S. Ascending uninterruptedly from Constantine, whose elevation is 2123 feet, the highest point is found between Batnah and Tizur, at only 3581 feet. In the part of the desert which lies between Biscara and Tuggurt, Fournel has succeeded in digging a series of artesian wells^[DN]. We learn from the old accounts of Shaw, that the inhabitants of the country were acquainted with a subterranean supply of water, and related fabulous tales of a “sea under the earth (bahr tôhl el-erd).” Fresh waters, which flow between clay and marl strata of the old chalk and other sedimentary formations, under the action of hydrostatic pressure, form gushing fountains when the strata are pierced^[DO]. The phenomenon of fresh water being often found near beds of rock salt, need not surprise the geognosist, acquainted with mining operations, since Europe offers many analogous phenomena.

92The riches of the desert in rock-salt, and its employment for purposes of building, have been known since the time of Herodotus. The salt zone of the Sahara (zone salifère du désert) is the most southern of the three zones which pass through Northern Africa from south-west to north-east, and is believed to be connected with the beds of rock-salt in Sicily and Palestine described by Friedrich Hoffman, and by Robinson^[DP].

The trade in salt with Sudan, and the possibility of cultivating the date-tree in the many Oasis-like depressions, caused probably by earth-slips in the beds of tertiary chalk or Keuper-gypsum, have equally contributed to animate the desert, at various parts, by human intercourse. The high temperature of the air, which renders the day’s march so oppressive across the Sahara, makes the coolness of the night (of which Denham and Sir Alexander Burnes frequently complained in the African and Asiatic deserts) so much the more remarkable. Melloni^[DQ] ascribes this coolness (which is probably produced by the radiation of heat from the ground), not to the great purity of the heavens (irraggiamento calorifico per la grande serenità di cielo nell’ immensa e deserta pianura dell’ Africa centrale), but to the extreme calm, and the absence of all movement in the air throughout the whole night^[DR].

The river Quad-Dra (Wadi Dra), which is almost dry the greater part of the year, and which, according to Renou^[DS], is one-sixth longer than the Rhine, flows into the Sahara in 32° north latitude, from the southern declivity of the Atlas of Morocco. It runs at first from north to south, until in 29° north lat., and 5° 8′ west long., it deflects at right angles to the west, and traversing the great fresh-water lake of Debaid, flows into the sea at Cape Nun, in lat. 28° 46′, and long. 11° 8′. This region, which was first rendered celebrated by the Portuguese discoveries of the fifteenth century, and whose geography has subsequently been shrouded in the deepest obscurity, is now known on the coast as the country of the Scheik of Beirouk 93(whose dominions are independent of the Emperor of Morocco). It was explored, in the months of July and August, 1840, by the French Count, Captain de Bouet-Villaumez, under the orders of his government. From manuscript and official reports it would appear that the mouth of the Quad-Dra is at present so much blocked up by sand as to have an open channel of only about 190 feet. The Saguiel-el-Hamra,—still very little known,—which comes from the south, and is supposed to have a course of at least 600 miles, flows into the same mouth at a point somewhat farther eastward. The length of these deep, but generally dry, river-beds is astonishing. They are ancient furrows, similar to those which I observed in the Peruvian desert at the foot of the Cordilleras, between the latter and the shores of the Pacific. In Bouet’s manuscript narrative^[DT], the mountains which rise to the north of Cape Nun are estimated at the great height of 9,186 feet.

It is generally supposed that Cape Nun was discovered in 1433 by the Knight Gilianez, despatched under the order 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 of the year 1351,—already contains the name of “Cavo di Non.” The doubling of this Cape was as much dreaded as has been since then the passage round Cape Horn; although it is only 23′ north of the parallel of Teneriffe, and might be reached by a few days’ sail from Cadiz. The Portuguese adage, “Quem passa o Cabo de Num, ou tornarà ou não,” could not intimidate the Infante, whose heraldic French motto of “Talent de bien faire,” well expressed his noble, enterprising, and vigorous character. The name of this Cape, which has long been supposed to originate in a play of words on the negative particle, does not appear to me to be of Portuguese origin. Ptolemy placed on the north-west coast of Africa a river Nuius, in the Latin version Nunii ostia. Edrisi refers to a town, Nul, or Wadi Nun, somewhat further south, and about three days’ journey in the interior, named by Leo Africanus Belad de Non. Several European navigators had penetrated far to the south of Cape Nun before the Portuguese squadron under Gilianez. The Catalan, Don Jayme Ferrer, in 1346, as we learn from the Atlas Catalan, published at 94Paris by Buchon, had advanced as far as the Gold River (Rio do Ouro), in 23° 56′ north lat.; while the Normans, at the close of the fourteenth century, reached Sierra Leone in 8° 30′ north latitude. The merit of having been the first to cross the equator in the Western Ocean incontrovertibly belongs, like so many other great achievements, to the Portuguese.