Part 8

[Footnote 1: The use of motor cars for reconnaissances in the Libyan Desert, initiated by the British Army during the Great War, has been considerably developed in the last few years by Prince Kemal el Din Hussein (son of the late Sultan of Egypt), who has made several long exploratory journeys with a fleet of cars of the caterpillar type, specially constructed so as to be capable of carrying considerable loads over sandy tracts which were impassable to the Army patrols. The expeditions organized and led by His Royal Highness have resulted in important additions to geographical knowledge concerning the Libyan Desert, especially the southern and western regions, which have hitherto been practically inaccessible. I had the pleasure of accompanying the Prince on three of his journeys, and am much indebted to him for thus affording me the opportunity of making many observations which would otherwise have been impossible to me. I have further to thank him for kind permission to illustrate this paper by reproductions from a selection of the excellent photographs taken by him during our travels.]

[Footnote 2: Kindly communicated by Mr. A. R. Boyce, Director of Sudan Surveys.]

[Footnote 3: Printed by the French Army Staff, 1926.]

[Footnote 4: By way of comparison, it may be remarked that the area (at the sea-level contour) of the Qattara depression is about four times that of the Dead Sea and Jordan Valley depression; but the latter (reckoning to the lowest point of the bed of the Dead Sea) is about six times the deeper of the two.]

[Footnote 5: A similar ambiguity of meaning very commonly attaches to Arabic geographical terms. Thus _beled_ may mean either a village or an entire country; _gebel_, either a mountain or a desert; _gezira_, either an island or a part of the Nile bank which is alternately covered and uncovered by the rise and fall of the river; _bir_, which properly signifies a well, is often used to denote a spring or a water-cistern; _wadi_, though its proper meaning is a valley, is also sometimes employed for a closed-in depression, as in the case of the Wadi Natrun.]

[Footnote 6: ‘Nouveaux Mémoires des Missions de la Compagnie de Jesus dans le Levant,’ Tome ii. (Paris, 1717), p. 74. This little book contains a map of Egypt, prepared by Father Sicard at Cairo in 1715, on which the “Mer sans eau” is shown with “bateaux petrifiez” depicted alongside it.]

[Footnote 7: See “Particulars concerning the Valley of the Natron Lakes, and that of the Old Bed of the River” (with map) by Andreossi, General of Artillery, in ‘Memoirs Relative to Egypt, Written in That Country during the Campaigns of General Bonaparte in the Years 1798 and 1799, by the Learned and Scientific Men who Accompanied the French Expedition’ (London, 1800), p. 270.]

[Footnote 8: See Rohlfs’ ‘Drei Monate in der libyschen Wüste’ (Cassel, 1875), p. 337; and Jordan’s ‘Physische Geographie und Meteorologie der libyschen Wüste’ (Cassel, 1876), p. 214.]

[Footnote 9: ‘Zeitschrift der Gesellschaft für Erdkunde zu Berlin,’ 1902, Tafel III.]

[Footnote 10: ‘Topography and Geology of the Fayum Province of Egypt’ (Cairo, 1905), p. 67.]

[Footnote 11: Since the above was written, the Professor of Geography at the new University of Cairo, M. Lorin, has suggested that at a former geological epoch the Nile flowed through Siwa Oasis and thence westward so as to make Cyrenaica an island. (See ‘L’Egypte,’ published by the Institut Français d’Archéologie Orientale, Cairo, in December 1926, p. 153.) M. Lorin does not give any grounds for this suggestion, and I know of no evidence that would justify its acceptance. As will be gathered from my remarks elsewhere in this paper, it seems to me far more likely that Siwa and the other northern depressions were in recent geological times regions of central drainage, than that they were local deepenings of a single channel; and in regard to earlier geological periods we possess too little information to form any conclusions as to drainage- lines.]

[Footnote 12: See Sir Hanbury Brown’s ‘The Fayum and Lake Moeris’ (London, 1892), pp. 40-48 and 106-110; Sir W. Willcocks’ ‘Perennial Irrigation and Flood Protection for Egypt’ (Cairo, 1894), also the same author’s ‘Egyptian Irrigation,’ third edition (London, 1913); Sir W. E. Garstin’s ‘Report on the Basin of the Upper Nile’ (Cairo, 1904), Appendix I. pp. 6-9; and Beadnell’s ‘Topography and Geology of the Fayum Province of Egypt’ (Cairo, 1905), pp. 16-24.]

[Footnote 13: ‘Report on the Administration of the Irrigation Department for 1895’ (Cairo, 1896), pp. 25-28.]

[Footnote 14: ‘Report on the Administration of the Irrigation Department for 1896’ (Cairo, 1897), p. 129.]

[Footnote 15: It may be remarked that even if a channel were to be cut from Lake Mariut to the Wadi Natrun it would still be necessary to continue pumping on a large scale from Lake Mariut to maintain the present-day drainage. According to returns communicated to me by the Irrigation Service, the quantity of water removed from Lake Mariut by pumping during the last nine years has averaged nearly 650 million cubic metres a year; and even on the most optimistic estimate of evaporation and seepage the Wadi Natrun could not be expected to dispose of half this quantity after the lapse of the few years which would be occupied in filling it to a permanent level.]

[Footnote 16: The average discharge of the Nile past Cairo in a year is 67 cubic kilometres. The capacity of the Qattara depression at the sea- level contour is roughly about 900 cubic kilometres.]

[Footnote 17: _Geogr. Journ._, 56 (1920), pp. 97-99 and 161-163.]

[Footnote 18: Lucas (‘Natural Soda Deposits in Egypt’ (Cairo, 1912), p. 15) regarded the water of the Wadi Natrun as being due to infiltration from the Nile, mainly on the ground that he supposed the water visibly entering the wadi (as small streams and trickles) to do so on the north- eastern side. But this, I think, is a mistake, as it neglects consideration of the large springs of warm fresh water which bubble up in and near the salt-lakes themselves, and also the large wells of the monasteries which lie south-west of the lakes.]

[Footnote 19: A far better site for this well would have been in the depression some 20 kilometres to the north-west, the ground-level at the lowest point of which is only 61 metres above sea; but at the time when the site of the well was chosen the existence of this depression was unknown.]

[Footnote 20: See Appendix III. in the second volume of Willcocks’ ‘Egyptian Irrigation,’ 1913, p. 853.]

[Footnote 21: Schweinfurth (_op. cit._, p. 855) even thought it might have percolated to Siwa, in spite of the great distance (480 kilometres) and the adverse direction of the difference of level between the two places.]

[Footnote 22: Mr. Beadnell (‘An Egyptian Oasis’ (London, 1909), p. 139) estimates the total discharge of the Kharga wells at 53,000 cubic metres per diem. We should not, I think, err greatly in estimating the total output of all the Egyptian oasis wells and springs at about five times this, or 250,000 cubic metres per diem. As the average daily discharge of the Nile in Egypt is about 180 million tons, a local influx into it several times as great as the total discharge of the oasis wells would represent but an insignificant addition to the discharge of the Nile. I think, however, that the influx of the warm water might possibly be detected by careful thermometric measurements made in the river near its banks at the time of low Nile.]

[Footnote 23: This was the lowest level recorded at the time when I drew the static contours on the map. The further exploration of the depression by Mr. Walpole in the present year has shown that at one place the ground-level descends to − 134 metres; the situation of this local deepening is, however, such that the drawing of the static contours would not have been affected by its inclusion in the list of adopted data.]

[Footnote 24: ‘An Egyptian Oasis’ (London, 1909), p. 156.]

[Footnote 25: “The Mutual Interference of Artesian Wells,” _Geol. Mag._ (London, 1909), pp. 23-26; also ‘An Egyptian Oasis,’ chap. x.]

[Footnote 26: ‘An Egyptian Oasis,’ p. 140.]

[Footnote 27: ‘Drei Monate in der libyschen Wüste’ (Cassel, 1875), p. 115.]

[Footnote 28: See Jordan’s ‘Physische Geographie und Meteorologie der libyschen Wüste’ (Cassel, 1875), p. 204. Jordan states that there were on an average not more than two to four plants per acre in this locality.]

[Footnote 29: See Rohlfs’ ‘Drei Monate in der libyschen Wüste’ (chapter ix. of which was written by Ascherson), p. 250.]

[Footnote 30: In my paper on ‘Recent Determinations of Geographical Positions in the Libyan Desert,’ published in Cairo in 1919, I gave (p. 14) the approximate position of the hill as lat. 24° 28′, long. 27° 45′. The position given above is from a more accurate determination which I made on revisiting the place with Prince Kemal el Din in 1923. On this latter occasion the excavations made by the Prince in the sand around the foot of the hill revealed the existence of hundreds of additional jars, many of them intact, set in regular order in the sand and obviously forming a water-dump. The majority of the jars bore clearly incised markings, which Prince Kemal el Din was able later to identify positively as being tribal marks of the Tebus, the marks being in fact exactly the same as those used by the Tebu tribes of the present day.]

[Footnote 31: See Jordan’s ‘Physische Geographie und Meteorologie der libyschen Wüste’ (Cassel, 1876), p. 215.]

[Footnote 32: ‘Kharga Oasis’ (Cairo, 1900), p. 57.]

[Footnote 33: _Geogr. Journ._, 42 (1913), p. 283; also ‘Mysteries of the Libyan Desert’ (London, 1925), p. 304.]

[Footnote 34: This “locus” is of course given by joining up the points of intersection of the 100-metre water-contour with the 200-metre ground-contour, the 200-metre water-contour with the 300-metre ground- contour, and so on.]

[Footnote 35: It is possible that the “Nubian Sandstone” in South- Western Egypt may represent more than one geological system, as has been found to be the case in Sinai. Col. Tilho (_Geogr. Journ._, 56 (1920), p. 259) records that the sandstone at Ennedi proved to be of Upper Silurian age by the fossils found in it.]

[Footnote 36: Though we passed within 10 kilometres to the east of Kissu on the return journey from Merga to Owenat in 1925, I could not observe the structure of the mountain very clearly, owing to haze. But it appeared to me to be a huge granitic intrusion rising through the gneiss which covers a large area hereabouts. The sandstone over which we had been travelling since leaving Merga gave place to gneiss about 40 kilometres before we came abreast of Kissu, and gneiss continued to be the country rock until we came within 30 kilometres of Gebel Owenat, when sandstone reappeared, at first capping low hills and then forming the plain.]

[Footnote 37: There exists no published English translation of Ptolemy’s ‘Geographia.’ Müller’s edition (Paris, 1883-1901) gives Greek and Latin texts, with a Latin commentary.]

[Footnote 38: Quoted in Müller’s edition of Ptolemy’s Geography, p. 739.]

[Footnote 39: For the latest delineation of this region, see the hypsometric map in the ‘Atlas de l’Algérie et de Tunisie,’ published by the Cartographic Service of the Algerian Government, Paris, 1924, Fascicule II.]

[Footnote 40: ‘Manual of Ancient Geography’ (London, 1891), p. 311.]

[Footnote 41: _Geogr. Journ._, 56 (1920), p. 94.]

[Footnote 42: ‘Mysteries of the Libyan Desert’ (London, 1925), p. 303.]

[Footnote 43: _Geogr. Journ._, 43 (1924), p. 288.]

[Footnote 44: ‘The Secret of the Sahara—Kufara’ (London, 1921), p. 235.]

[Footnote 45: Beadnell, “The Sand-dunes of the Libyan Desert,” _Geogr. Journ._ 25 (1910), pp. 379-395; Harding King, “The Nature and Formation of Sand Ripples and Dunes,” _Geogr. Journ._, 47 (1916), pp. 189-209; Harding King, “Study of a Dune Belt,” _Geogr. Journ._, 51 (1918), pp. 16-33, and Discussion, pp. 250-258.]

[Footnote 46: For particulars of the distribution and directions of the dune-lines near Gebel Owenat, and between that mountain and Sarra, I am indebted to Prince Kemal el Din Hussein, who devoted special attention to observing them on his expedition to Sarra in 1926.]

[Footnote 47: It may be remarked that in the desert of Northern Sinai the dune-lines follow curved directions, instead of maintaining a single direction as in the Egyptian Libyan Desert, and this curvature of the Sinai dune-lines has generally been thought to be caused by the deflecting influence of the mountain masses of Moghara, Yelleg, and Hellal on the wind; but here also there may be regional influences at work.]

[Footnote 48: See Jordan’s notes on pp. 204 and 208 of his “Physische Geographie und Meteorologie der libyschen Wüste,” Cassel, 1876.]

[Footnote 49: _Geogr. Journ._, 49 (1917), p. 55.]

[Footnote 50: The steep Miocene escarpment, some 200 metres high, which bounds the Qattara depression on the north, probably produces a great eddy in the wind sweeping southwards over it, causing a whirl round a horizontal axis south of the scarp; this may be very influential both in excavation and in lifting the sand to great heights. As a large portion of the floor of the depression at the foot of the escarpment is formed of a salty sludge (sabakha), it is likely that a considerable quantity of finely divided salt crystals are carried up with the sand in summer, and this may conceivably act to some extent as a binding material in the dunes.]

[Footnote 51: _Geogr. Journ._, 47 (1916), p. 209.]

[Footnote 52: _Geogr. Journ._, 51 (1918), p. 252.]

[Footnote 53: Many years ago I discovered that this film can be removed by treating the sand with warm hydrochloric acid, leaving the grains of snowy whiteness (see my ‘Description of the First or Aswan Cataract’ (Cairo, 1907), p. 57). But I think traces of iron in the ferrous state must exist even within the white siliceous body of the grains, and be continually passing into the ferric state at the exposed surface; for otherwise it is difficult to account for the persistence of the yellow colour in spite of the mutual rubbing of the grains during their transport by wind. The film may possibly have an influence on the electrical behaviour of the grains, by reason of its possessing a higher conductivity than the silica of the interior.]

[Footnote 54: Professor P. E. Shaw has quite recently (_Nature_, vol. 118 (1926), p. 659) suggested from laboratory experiments that the mutual _impact_ of particles of _identical_ nature in sandstorms may result in electrification of the particles and of the air with charges of opposite signs. I think most travellers in the desert have, like myself, formed the impression that electrification of the air is more pronounced during sandstorms (khamsins) than at other times. But it is curious that observations made with the electrograph at Helwan Observatory do not seem altogether to bear this out. Dr. Hurst finds that khamsins are usually accompanied by low values of potential gradient in their early stages, with great disturbances both positive and negative for some hours before and after the break of the khamsin (‘Observations on Atmospheric Electricity at Helwan Observatory,’ Survey Dept. Paper No. 10 (Cairo, 1909), pp. 52-62).]

[Footnote 55: Hurst, _op. cit._, p. 28.]

[Footnote 56: Mr. Harding King records in his paper of 1915 that he found sand-grains blown off the dunes to be electrified; can these have been grains which became charged by jumping up from the dune to meet others and thus sharing their charge?]

[Footnote 57: _Geogr. Journ._, 35 (1910), p. 385.]

[Footnote 58: The hot and disagreeable south and south-west winds which blow during the “khamsins” of the spring are much less constant in their direction; and though they produce thick sandstorms, they have always seemed to me to occasion rather a general scattering of the sand over the surface of the desert than to form deposits having very definite arrangement; moreover, they blow on relatively few days of the year. The far more prevalent cool strong north-north-west winds, on the other hand, often scarcely vary a point in direction for days together, and their coincidence with the direction of the dune-lines is very pronounced.]

[Footnote 59: _Zeitschrift der Gesellschaft für Erdkunde zu Berlin_, 1902, p. 760.]

[Footnote 60: ‘Recent Determinations of Geographical Positions in the Libyan Desert,’ Survey Department Paper No. 34, 1919. p. 14.]

[Footnote 61: _Geogr. Journ._, 44 (1924), p. 377.]

[Footnote 62: Jordan’s final position was lat. 25° 11′ 7″, long. 27° 25′ 0″. The longitude given on the document found in the bottle at the cairn (14° 42′ E. of Berlin, or 28° 3′ 42″ E. of Greenwich) was a preliminary value resulting from Jordan’s observation of a lunar distance, and was wrong by some 40 miles.]

[Footnote 63: Mr. Harding King’s observations gave the latitude as 26° 30′ 46″, and the longitude as 27° 36′ (see his map in _Geogr. Journ._, 42 (1913), p. 516).]

[Footnote 64: ‘Recent Determinations of Positions in the Libyan Desert,’ Survey Department Paper No. 34 (Cairo, 1919), p. 12.]