Part 1

[Transcriber's note: This article has been extracted and prepared from _The Geographical Journal_, v. 70, 1927.]

PROBLEMS OF THE LIBYAN DESERT

John Ball, O.B.E., D.Sc., M.Inst.C.E., F.G.S., Director of Desert Surveys, Egypt

_Map following p._ 96.

THERE can be few tracts of the Earth’s surface which present such a number and variety of interesting geographical problems as the Libyan Desert. The following are some of the more puzzling of the questions which have been asked at various times since I made my first acquaintance with the desert thirty years ago:

1. Did the Nile, or a branch of it, ever flow through the Libyan Desert to the west of the present Nile Valley?

2. By what natural agency were the great depressions in the Libyan Desert excavated?

3. Can other depressions in this region, besides the much-discussed Wadi Rayan, be considered possible of utilization in connection with irrigation, flood-protection, or drainage of the Nile Delta, or as sources of water-power for Egypt?

4. Whence comes the artesian water of the oases?

5. Why have not certain lakes, such as Sittra and Bahrein, situated as they are in an almost rainless region, long since dried up?

6. Can the present scanty supplies of drinkable water derived from local rainfall along the Egyptian Mediterranean Littoral be supplemented by artesian borings?

7. Are the artesian water-supplies of the oases gradually diminishing?

8. Where shall we look for the mysterious “Zerzura,” or “Oasis of the Blacks”? Are there any other “lost” oases remaining to be discovered?

9. Can the present difficulties of travel in the Libyan Desert, which are chiefly due to scarcity of water, be alleviated by the sinking of new wells?

10. Where are the “Tortoise Marshes” of Ptolemy?

11. What determined the peculiar distribution of the sand-dunes, some of which extend in straight lines for hundreds of kilometres?

12. What is the full extent of the distribution of flint implements and pottery, of which accumulations have been found in what are now among the most desolate parts of the desert, and what light does this throw on human history and climatic changes?

To most of these questions no completely satisfactory answers have as yet been given, though several of them have been the subject of painstaking investigations by many workers. Our knowledge of the facts bearing on them has, however, increased considerably during the past few years; and in the present paper I propose briefly to review the various questions in the light of the latest available data concerning them.

The problems, though they concern a variety of subjects, are very much interwoven with each other, and they are mostly alike in that the first difficulty in any attempt to solve them has always been the incompleteness of our geographical knowledge concerning the Libyan Desert as a whole. If we possessed a series of detailed contour-maps covering the whole of the desert, most of the problems would be in a fair way of solution. But the surveys which would be necessary for such a result are impracticable at present, mainly on the score of expense.

Some fifteen years ago I essayed the construction of a contoured map of the Libyan Desert, in connection with the International “Million” map of the world. But I had to give up the task, finding that there were vast areas without a single observation for altitude, while such altitude- data as did exist were open to errors of a magnitude intolerable for even a preliminary contouring of the areas with which they were concerned. The attempt however was not without its value, because it drew attention to the great lack of reliable levels in the Libyan Desert, and to the necessity of remedying this defect before even an approximately true picture of the general relief could be obtained.

In the interval which has elapsed since my former attempt, a great deal of surveying has been carried out in the Libyan Desert, and in most of this work special attention has been paid to the matter of levels. Two long chains of triangulation have been run westward from the Nile to Siwa Oasis, one _viâ_ the Wadi Natrun and the other _viâ_ Baharia Oasis; another chain has been completed along the coast westward from Alexandria to Sollum, and a triangulation is now being carried out which will eventually connect the oases of Kharga and Dakhla with the Nile Valley. Small local triangulations have also been made in certain areas, such as Dakhla Oasis and in the neighbourhood of Owenat. In all these triangulations vertical as well as horizontal angles have been observed, so that reliable trigonometric altitudes are now available for almost all the points occupied or sighted. In the southern and central parts of the desert, we are still dependent on barometric levels; but the old determinations have mostly been replaced by later and better ones; and the use of motor-car transport, by facilitating exploratory journeys in hitherto untrodden regions, has permitted of a large number of additional determinations being made in tracts where no previous observations of any kind existed.[1]

Owing to the methods employed in the latest barometric determinations, the resulting altitudes are of a much higher order of accuracy than could be hoped for in previous measurements of the kind; in fact, it is believed that they are not so very far behind trigonometric levels in precision. This increased accuracy has been rendered possible by the collaboration of the Egyptian Meteorological Service, which, thanks to the abundant weather-data now received and dealt with by it, is in a position to furnish a close approximation to the sea-level pressure at any point in the deserts at any given instant. The aneroids used in the desert explorations are compared with the standard barometer of the Meteorological Service immediately before the start and immediately after the return of each expedition. At each observation in the desert, the date and time, and the temperature of the air, are noted, as well as the approximate latitude and longitude of the place. On the return of the expedition, the recorded reading is corrected for the error of the aneroid on the standard barometer, and the Meteorological Service is asked to supply the sea-level pressure at the particular place and time of the observation. From the difference of the two pressures and the air temperature, the height of the place above sea-level is then worked out directly with the aid of Jordan’s table of “Barometrische Höhenstufen.” If the place of observation lies considerably above sea-level, a small correction is applied to the observed air-temperature to allow for the temperature-gradient in the air; for of course it is the mean temperature of the air column between the place and sea-level which should be employed in the reduction.

It is unlikely that with this procedure either the sea-level pressures or those observed at the places can be in error by much more than half a millimetre; and consequently, even with some slight uncertainties in the air-temperatures, the resulting altitudes may be expected to be accurate to within about 15 metres when only a single observation has been made, and to within much less than this when, as is usually the case at important points, the altitudes have been calculated from a series of readings spread over several days. That this degree of accuracy is actually attained seems evident on comparison of the levels obtained for the same places on different dates. Thus, for instance, at a camp close to Bir Terfawi, during a stay of five days in January and two days in March 1925, I made in all eighteen aneroid observations. The mean altitude found was 244 metres; the average deviation of a single observation from this mean was 8 metres, the maximum being 16. On the assumption that all sources of error are accidental, the probable error of the mean resulting altitude works out at less than 2 metres, which is about the same as might be expected in trigonometric levelling to the place from the Nile Valley.

The points in the interior of the Libyan Desert of which the levels are fairly accurately known now number many hundreds, and with the exception of a large blank in the unexplored west, and another between the Nile and Merga in the Northern Sudan, they are fairly well distributed over the country. It therefore seemed to me to be worth while to make another attempt at a contoured map; for the levels now known (though still far too few for contours to be drawn with any great precision) might suffice for the construction of a map on a comparatively small scale and with contours at fairly wide intervals; it was felt that a provisional map of this kind, besides affording at least an approximate general view of the relief, might help towards the solution of one or more of the problems which I have mentioned above. I commenced by sketching in the contours at 100-metre intervals on the original sheets of the 1:500,000 map of Egypt, a revised edition of which is in preparation. They were then reduced to the million scale, and afterwards still further reduced, with additions from my own recent observations around Owenat, Gebel Kissu, and Merga, from Hassanein Bey’s records of his journey between Jalo and El Fasher, from the altitude-data obtained by the Anglo-French Boundary Commission in the Sudan,[2] and from the maps of Prince Kemal el Din’s expedition of 1926 to Owenat and Sarra Well,[3] to form the map following p. 96. The attempt has, I think, fully justified itself, and more than fulfilled the hopes that were entertained concerning it.

Probably the feature that will first strike the attention on glancing at the contoured map is the series of depressions below sea-level stretching westward from near Cairo to Jarabub. The following table gives a list of the principal of these depressions, with the approximate extent of the areas lying below sea-level, and also (where known) the depths below sea-level of their deepest parts. Where the lowest part is covered by a lake, the depth shown is that of the water-surface, not that of the lake-bottom:

_Approximate area _Approximate _Depression._ below sea-level depth of deepest in sq. kiloms._ part below sea in metres._

Wadi Natrun 220 23

Faiyum 700 45

Wadi Rayan 280 43

Qattara (including Moghara, 18,000 134 Qara, and Tebaghbagh)

Sittra (including Timata) 300 33

Bahrein (including Nuemisa) 150 15 (?)

Watiya 70 15

Areg 60 25

Siwa (including Maasir and 800 17 Maraqi)

Girba 20 (?)

Kheiba 40 (?)

Shiyata 20 (?)

Melfa (including Shebat, 260 18 (?) Exabia, and Gagub)

As will be seen from the figures in the table, by far the largest and deepest depression in this series—seven times as large, in fact, as all the others put together—is that of Qattara, which has not been shown on any previous map, and of which the existence was proved only last year. That so deep a depression should exist comparatively near to the Mediterranean and to Cairo, and have remained undiscovered until now, is striking evidence of how much has still to be learned concerning the configuration of the desert surface. The manner in which the discovery was made is perhaps worth placing on record. Hearing early in 1917 that a military patrol was about to operate in the Qattara region, I lent a small aneroid to the officer in charge of the patrol, and asked him to take readings with it at various points along his route, with the object of getting some idea of the altitudes in that region. It was, of course, certain that low-lying country existed along the foot of the Qattara escarpment, but no idea was entertained that any great part of it might be below the level of the sea. The officer brought back aneroid-readings which seemed to indicate that the spring at the foot of the scarp at Qattara was about 60 metres below sea-level; but the aneroid itself was unfortunately lost during the return journey. The result was too surprising for it to be accepted without evidence that the readings of the instrument had not been vitiated by accidental rough treatment, and consequently I refrained at the time from placing the levels found on the maps. But I resolved to confirm them or otherwise on the first opportunity.

That opportunity came last year, when it was possible to send a survey- party to triangulate westwards from the Wadi Natrun so as to cross the place where the aneroid readings had been taken. The work was entrusted to Mr. G. F. Walpole, of the Survey of Egypt, who had already distinguished himself by successfully carrying out a difficult triangulation from the Nile across some 500 kilometres of the Libyan Desert _viâ_ Baharia to Siwa. The result of Mr. Walpole’s work was not only to confirm the substantial accuracy of the previous estimation of the level of the Qattara spring, but to bring to light the existence of a vast hollow, thousands of square kilometres of whose floor lie at even lower levels, and which at one place descends to a depth of no less than 134 metres below the level of the sea.[4] This last-mentioned spot, some 100 kilometres south-south-west of the Qattara spring, is probably the lowest-lying point on the land-surface of the African continent.

A scarcely less remarkable feature is the series of depressions comprising the oases of Kharga, Dakhla, Abu Mungar, and Farafra; while Baharia occupies a more isolated position about midway between Farafra and the Faiyum. In contrast with those of the northern series, these southern depressions do not penetrate to sea-level. The lowest points in Kharga Oasis are probably at or just below the level of the sea, but the general level of the Kharga floor is about 70 metres above that datum. The lowest point of Farafra is somewhat higher than the general level of Kharga; those of Dakhla and Abu Mungar are higher still, while in Baharia, though it lies farther to the north, the floor-level averages some 130 metres above sea.

A noteworthy thing about the larger depressions is that their northern boundaries are formed by steep escarpments, while to the south the slope is more gradual. This is the case, for instance, with the Faiyum, Qattara, Siwa, Kharga, Dakhla, Abu Mungar, and Farafra. Baharia is unique in being entirely surrounded by escarpments, as also in containing a large number of hills approximating in height to that of the bounding scarps. In the majority of cases the greater steepness of the northern boundaries can be correlated with geological structure; the northern walls of the Qattara and Siwa depressions, for instance, mark the southern limit of certain Miocene strata, while those of Kharga and Dakhla coincide with the southern limit of the Eocene limestones.

To the south-west of Dakhla Oasis there stretches a broad tract of rising ground, with the Gilf Kebir and the peaks of Arkenu, Owenat, and Kissu as conspicuous features. On either side of this tract the general level falls, on the one hand towards Kufra and Cyrenaica, and on the other hand towards the Nile. The Gilf Kebir is a great broken plateau of sandstone, rising very nearly to the 1000-metre contour and stretching in a direction a little west of south for over 100 kilometres. I saw the south end of this plateau from several points on the way from Terfawi to Owenat when travelling with Prince Kemal el Din in 1925, and fixed its position by compass-bearings. As seen from the south, the plateau appeared to be merely a flat-topped hill; its true form and extent were discovered by the Prince in the following year, when he passed along its eastern foot on his way from Pottery Hill to Owenat. The highest peak of Arkenu, in about lat. 22° 17′, long. 24° 46′, I estimated to rise to approximately 1410 metres above sea. The altitude of Gebel Owenat far transcends Hassanein Bey’s previous estimate of 1100 metres; a trigonometric measurement which I made in 1925 gave its summit as 1907 metres above sea. The general level of the ground at the foot of Owenat I found to average about 600 metres, thus agreeing with Hassanein Bey’s figures. Gebel Kissu, though lower than Gebel Owenat, is considerably higher than Gebel Arkenu, and being an isolated mountain with a single well-marked peak, it forms a very conspicuous landmark; my trigonometric determination gave 1726 metres for the altitude of the peak above sea.

To the south-west of Kissu there are a few widely scattered isolated hills, but the country in general forms a rolling plain of sand extending to the north-east corner of French Equatorial Africa with a nearly uniform level of about 700 metres. Beyond the French boundary the ground rises towards the Erdi Hills, which attain over 1000 metres.

From the corner of French Equatorial Africa to Merga, a distance of 250 kilometres, the country consists of alternations of sand-plains and flat stony tracts, with a very gradual fall to a level of about 560 metres at the edge of the Merga depression.

Between Merga and Owenat the country consists of sandy plains alternating with broken stony ground and occasional hills. The general level rises from about 570 metres on the northern side of the Merga depression to nearly 800 metres on the parallel of 20° 30′, then gradually falls to about 600 metres at the foot of Gebel Owenat.

1. _Did the Nile, or a Branch of it, ever flow through the Libyan Desert to the Mediterranean?_

The idea that a “dry river” exists in the Libyan Desert is a very old one, and seems to have had its origin in the fact that barren depressions in that region are sometimes called by the local Arabs _Bahr bela ma_, that is, “sea without water.” But the Arabic word _bahr_, which properly means a sea or a lake, as in Bahr Lot (the Dead Sea), is also applied in Egypt and the Sudan to a river, as in Bahr el Nil (the Nile) and Bahr el Azrak (the Blue Nile).[5]

The earliest depression to be discovered bearing the name of _Bahr bela ma_ was the one now known as the Wadi Faregh (the “empty wadi”), situated immediately south of the Wadi Natrun. Father Sicard, who visited the place in 1712, correctly interpreted the Arabic name to mean literally “sea without water,” and having discovered fossil trees there, which he imagined to be the petrified remains of masts of ships, he inferred that a narrow arm of the sea formerly extended from the Mediterranean into the locality.[6] At a later date Sicard’s view that the petrified trees were the masts of ships was recognized to be a mistaken one; but a greater error was committed by changing the translation of _Bahr bela ma_ from “sea without water” into “river without water,” as was done by D’Anville in his ‘Mémoires sur l’Egypte,’ published at Paris in 1766. D’Anville was a great authority in his day, and his translation was adopted by subsequent writers for over a hundred years. General Andreossi, who commanded Napoleon’s artillery in the expedition of 1798 and 1799, made a map of the “Dry River” and the “Valley of the Natron Lakes,” in which both depressions are shown open at both ends, instead of being closed in as they really are. Andreossi considered that the “Bahr bela ma” was the dry bed of an ancient branch of the Nile, which left the present Nile Valley somewhere in Middle Egypt and entered the sea to the west of Alexandria; he also thought that the ancient Lake Moeris was probably formed by the damming of the “dry river” near its supposed offtake from the Nile.[7] Later on, after Cailliaud and other early nineteenth-century travellers had discovered that other depressions existed in widely separated localities and bore the same Arabic name of _Bahr bela ma_, it seems to have been hastily assumed by the cartographers of the time that all the depressions bearing the same name were parts of a single dried-up river-channel. Thus, on a large map of Egypt compiled by Colonel Lapin and published at Paris in 1856, the “Bahar Belah-mah ou Fleuve sans eau” is stated to come from the Congo and is depicted as coursing through the Oasis of Dakhla, thence passing to the east of Baharia Oasis and on to the Mediterranean. On another large map of Egypt, compiled by Muzzi Bey, the then Director-General of Egyptian Posts, and published in Florence in 1876, a continuous valley is boldly shown leading from the mountains of Darfur to the Mediterranean, while cross-valleys, labelled “Old Bed of the Nile,” are depicted as connecting the main valley with that of the Nile at Korosko and Dongola.

The Rohlfs expedition of 1874 proved that there was no such channel running northwards through Dakhla Oasis; that the “Bahr bela ma” which had been crossed by Cailliaud between Siwa and Baharia was merely a closed-in local depression, and that the continuous empty river-beds which were shown on the maps of that period had no real existence.[8]

But though the continuous “Bahr bela ma” channel of the old cartographers has been shown to be purely imaginary, and has in consequence disappeared from our modern maps, the belief that an old dry river-bed _may_ exist _somewhere_ in the Libyan Desert has apparently persisted in many minds even to our own day. Only a few years ago I was called upon by the Government to discuss a suggestion, made in all seriousness by a person of considerable eminence, that the Nile, or a branch of it, must at one time have followed a course from somewhere near Dongola through some of the Egyptian oases to the Mediterranean; and that by tracing out the old channel, and deepening it artificially where necessary, a part of the river might be taken off along this path and its water utilized to irrigate the desert country on either side of it. To the few scientific travellers who have journeyed extensively in the Libyan Desert, it will doubtless appear incredible that such a suggestion as this could be seriously made. But old traditions concerning the geography of little-known regions die hard, and this particular one has probably been fostered by the circumstance that on most small-scale maps the oasis-depressions have been shown without any precise indication of the altitude of the intervening ground, as well as by the speculations of geologists as to the existence of a river in the region in past geological ages. Blanckenhorn, for instance, published in 1902 a series of small-scale maps depicting the course of a hypothetical river, the “Libyan Ur-Nile,” running northwards through the desert in the Eocene and Oligocene periods, and ceasing to exist in the Pliocene.[9]