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+ font-size: 90%; +} +.ipubr { + text-indent: 0; + margin-top: 0; + text-align: right; + font-size: 70%; +} +.ipubr2 { + text-indent: 0; + margin-top: 0; + text-align: right; + font-size: 75%; +} +img { + width: inherit; + max-width: 100%; +} +.iw1 { width: 1000px; } +.iw2 { width: 600px; } +.iw3 { width: 350px; } +</style> +</head> +<body> +<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 77091 ***</div> +<div class="margins"> +<div class="transnote"> +<p class="center">This article has been extracted and prepared from +<em>The Geographical Journal</em>, v. 70, 1927.</p> + +<p class="center x-ebookmaker-drop">Large-size versions of maps and +diagrams are available by clicking on them.</p> +</div> + +<h1><span class="pagenum" id="Page_21">[No. 1<br> +21]</span>PROBLEMS OF THE LIBYAN DESERT</h1> + +<p class="center">John Ball, O.B.E., D.Sc., M.Inst.C.E., F.G.S., +Director of Desert Surveys, Egypt</p> + +<p class="center"><em><a href="#map2">Map</a> following p.</em> +96.</p> + +<p class="dcap space-above15">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:</p> + +<p class="pad4"><a href="#s01">1.</a> Did the Nile, or a branch of +it, ever flow through the Libyan Desert to the west of the present +Nile Valley?</p> + +<p class="pad4"><a href="#s02">2.</a> By what natural agency were +the great depressions in the Libyan Desert excavated?</p> + +<p class="pad4"><a href="#s03">3.</a> Can other depressions in this +region, besides the much-discussed Wadi Rayan, be considered +possible of utilization in<span class="pagenum" id= +"Page_22">[22]</span> connection with irrigation, flood-protection, +or drainage of the Nile Delta, or as sources of water-power for +Egypt?</p> + +<p class="pad4"><a href="#s04">4.</a> Whence comes the artesian +water of the oases?</p> + +<p class="pad4"><a href="#s05">5.</a> Why have not certain lakes, +such as Sittra and Bahrein, situated as they are in an almost +rainless region, long since dried up?</p> + +<p class="pad4"><a href="#s06">6.</a> Can the present scanty +supplies of drinkable water derived from local rainfall along the +Egyptian Mediterranean Littoral be supplemented by artesian +borings?</p> + +<p class="pad4"><a href="#s07">7.</a> Are the artesian +water-supplies of the oases gradually diminishing?</p> + +<p class="pad4"><a href="#s08">8.</a> Where shall we look for the +mysterious “Zerzura,” or “Oasis of the Blacks”? Are there any other +“lost” oases remaining to be discovered?</p> + +<p class="pad4"><a href="#s09">9.</a> 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?</p> + +<p class="pad4"><a href="#s10">10.</a> Where are the “Tortoise +Marshes” of Ptolemy?</p> + +<p class="pad4"><a href="#s11">11.</a> What determined the peculiar +distribution of the sand-dunes, some of which extend in straight +lines for hundreds of kilometres?</p> + +<p class="pad4"><a href="#s12">12.</a> 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?</p> + +<p>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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id= +"Page_23">[23]</span> 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.</p> + +<p>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 <em>viâ</em> the Wadi +Natrun and the other <em>viâ</em> 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.<a id="FNanchor_1"></a><a href="#Footnote_1" +class="fnanchor">[1]</a></p> + +<p>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,<span class="pagenum" id="Page_24">[24]</span> 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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id= +"Page_25">[25]</span> 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,<a id="FNanchor_2"></a><a href="#Footnote_2" class= +"fnanchor">[2]</a> and from the maps of Prince Kemal el Din’s +expedition of 1926 to Owenat and Sarra Well,<a id= +"FNanchor_3"></a><a href="#Footnote_3" class="fnanchor">[3]</a> to +form the <a href="#map2">map</a> following p. 96. The attempt has, +I think, fully justified itself, and more than fulfilled the hopes +that were entertained concerning it.</p> + +<p>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:</p> + +<table class="tless" id="t025"> +<tr> +<th><em>Depression.</em> +</th> +<th class="width5"><em>Approximate area below sea-level in sq. +kiloms.</em> +</th> +<th class="width5"><em>Approximate depth of deepest part below sea +in metres.</em> +</th> +</tr> + +<tr> +<td class="tdl-top hang1">Wadi Natrun</td> +<td class="tdr-bot pad-right1">220</td> +<td class="tdc-bot">23</td> +</tr> + +<tr> +<td class="tdl-top hang1">Faiyum</td> +<td class="tdr-bot pad-right1">700</td> +<td class="tdc-bot">45</td> +</tr> + +<tr> +<td class="tdl-top hang1">Wadi Rayan</td> +<td class="tdr-bot pad-right1">280</td> +<td class="tdc-bot">43</td> +</tr> + +<tr> +<td class="tdl-top hang1">Qattara (including Moghara, Qara, and +Tebaghbagh)</td> +<td class="tdr-bot pad-right1">18,000</td> +<td class="tdc-bot">134</td> +</tr> + +<tr> +<td class="tdl-top hang1">Sittra (including Timata)</td> +<td class="tdr-bot pad-right1">300</td> +<td class="tdc-bot">33</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bahrein (including Nuemisa)</td> +<td class="tdr-bot pad-right1">150</td> +<td class="tdc-bot">15 (?)</td> +</tr> + +<tr> +<td class="tdl-top hang1">Watiya</td> +<td class="tdr-bot pad-right1">70</td> +<td class="tdc-bot">15</td> +</tr> + +<tr> +<td class="tdl-top hang1">Areg</td> +<td class="tdr-bot pad-right1">60</td> +<td class="tdc-bot">25</td> +</tr> + +<tr> +<td class="tdl-top hang1">Siwa (including Maasir and Maraqi)</td> +<td class="tdr-bot pad-right1">800</td> +<td class="tdc-bot">17</td> +</tr> + +<tr> +<td class="tdl-top hang1">Girba</td> +<td class="tdr-bot pad-right1">20</td> +<td class="tdc-bot">(?)</td> +</tr> + +<tr> +<td class="tdl-top hang1">Kheiba</td> +<td class="tdr-bot pad-right1">40</td> +<td class="tdc-bot">(?)</td> +</tr> + +<tr> +<td class="tdl-top hang1">Shiyata</td> +<td class="tdr-bot pad-right1">20</td> +<td class="tdc-bot">(?)</td> +</tr> + +<tr> +<td class="tdl-top hang1">Melfa (including Shebat, Exabia, and +Gagub)</td> +<td class="tdr-bot pad-right1">260</td> +<td class="tdc-bot">18 (?)</td> +</tr> +</table> + +<p>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<span class="pagenum" id="Page_26">[26]</span> 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.</p> + +<p>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 <em>viâ</em> 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.<a id="FNanchor_4"></a><a href="#Footnote_4" +class="fnanchor">[4]</a> 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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id= +"Page_27">[27]</span> 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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<h2><span class="pagenum" id="Page_28">[28]</span><a id= +"s01"></a>1. <em>Did the Nile, or a Branch of it, ever flow through +the Libyan Desert to the Mediterranean?</em></h2> + +<p>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 <em>Bahr bela ma</em>, that is, “sea without water.” But the +Arabic word <em>bahr</em>, 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).<a id="FNanchor_5"></a><a href="#Footnote_5" class= +"fnanchor">[5]</a></p> + +<p>The earliest depression to be discovered bearing the name of +<em>Bahr bela ma</em> 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.<a id="FNanchor_6"></a><a href="#Footnote_6" class= +"fnanchor">[6]</a> 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 +<em>Bahr bela ma</em> 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.<a id="FNanchor_7"></a><a href= +"#Footnote_7" class="fnanchor">[7]</a> Later on, after Cailliaud +and other<span class="pagenum" id="Page_29">[29]</span> early +nineteenth-century travellers had discovered that other depressions +existed in widely separated localities and bore the same Arabic +name of <em>Bahr bela ma</em>, 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.</p> + +<p>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.<a id="FNanchor_8"></a><a href= +"#Footnote_8" class="fnanchor">[8]</a></p> + +<p>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 <em>may</em> exist <em>somewhere</em> 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<span class="pagenum" id="Page_30">[30]</span> +Ur-Nile,” running northwards through the desert in the Eocene and +Oligocene periods, and ceasing to exist in the Pliocene.<a id= +"FNanchor_9"></a><a href="#Footnote_9" class="fnanchor">[9]</a></p> + +<p>That a river flowed during late Eocene or early Oligocene times +in a north-easterly direction through what is now the Libyan +Desert, and entered a sea near what is now the Faiyum, can scarcely +be questioned; for it is only by the existence of such a river that +we can account for the assemblage of fossil trees and curious +remains of Eocene animals (including the ancestors of the elephant) +discovered by Mr. Beadnell north of the Birket el Qarun and +described by the late Dr. Andrews.<a id="FNanchor_10"></a><a href= +"#Footnote_10" class="fnanchor">[10]</a> As to the size, length, +and exact position of this river of the geological past there is +very great doubt; but neither its situation nor even its existence +can be considered material to our present inquiry. No one +conversant with the known facts bearing on the general geological +history of Egypt during late Tertiary and Quaternary times could +make the mistake of thinking that the path of an Eocene river might +be traceable in the present desert relief. The evidences of such +path must be purely of a geological nature. In his endeavours to +suggest what might possibly have been the course of the river on +whose banks the Eocene animals lived, Mr. Beadnell found in two +localities deposits which might have been formed along the ancient +drainage-line; and in both these localities the deposits now occupy +the summits of hills. There is insufficient evidence of any kind to +justify so exact a location of the Eocene river as Blanckenhorn’s +maps would suggest, and none whatever of any relationship, either +between the present surface-configuration of the desert and Eocene +or Oligocene drainage-lines, or between those drainage-lines and +the River Nile. The appellation “Ur-Nile” of Blanckenhorn is thus a +misleading one. If we are to look for traces of a dried-up river in +the surface-forms of the Libyan Desert of to-day, it must be a +river which, like the streams which eroded the great wadis of the +Eastern Desert, existed in geologically recent times, and which +became dry either through the continual deepening of the present +Nile-channel, with consequent capturing of the former drainage, or +through climatic changes causing a diminution of rainfall in the +collecting area.</p> + +<p>A study of the contoured map seems to me to be absolutely +conclusive on the question at issue, for it indicates clearly that +at no time within the geologically recent period can there have +been any such continuous channel as has been supposed. Let us try +and trace, with the aid of the map, the most likely course along +which the ancient Libyan Nile-branch, if ever one existed, must +have flowed. Starting from the Nile in the neighbourhood of +Dongola, we observe that the lowest possible track is through Sheb +towards Kharga. But Sheb can only be reached after passing over +some 350 kilometres of desert lying well above the level of the +Nile at Dongola, which is about 230 metres above sea. It is, of +course, quite<span class="pagenum" id="Page_31">[31]</span> +conceivable that even within geologically recent times the Nile at +Dongola may have been considerably above its present level; so that +we may pass over this first difficulty as not being definitely +conclusive against the hypothesis we are pursuing. From Sheb to the +south end of the Kharga depression there is a drop of about 160 +metres, so that up to this point a channel may have been possible. +But from here onwards, difficulties come in. If we turn northwards, +we soon encounter the north wall of Kharga, rising to 300 metres +above sea-level; so there is no continuing that way. Instead, we +turn westwards towards Dakhla. But from Kharga we have to pass over +ground reaching very nearly to the 200-metre contour for some 80 +kilometres to enter the Dakhla depression, where we drop to a level +of 119 metres. We have to traverse some 15 kilometres at altitudes +above 200 metres to reach Abu Mungar, where the level is 117 +metres; then a further 12 kilometres lying above the 200-metre +contour to get to Farafra, where the level descends to about 90 +metres. To get out of Farafra, we have again to traverse country +lying over 200 metres above sea, whether we choose a north-westerly +route <em>viâ</em> Sittra to the Qattara depression, or a +north-westerly one <em>viâ</em> Baharia to the Wadi Rayan and the +Faiyum. Taking the first of these alternatives as being the +shorter, we cross some 30 kilometres of ground above the 200-metre +level, and a further 120 kilometres lying between the 200- and +100-metre contours, before reaching the Qattara depression. And +once we are in the Qattara depression (the lowest point of which is +134 metres below sea), there is no possibility of reaching the +Mediterranean except by crossing a considerable tract where the +ground-level is over 100 metres above sea-level.</p> + +<p>A section of the route described, with a comparison-line passing +through the present Nile-levels in corresponding latitudes, is +shown in the figure below:</p> + +<div class="figcenter iw2"> +<figure id="map1"><a href='images/map1.jpg'><img src= +'images/map1.jpg' alt=''></a> +<p class="cp2"><em>Profile from the Nile at Dongola through the +depressions of Kharga, Dakhla, Abu Mungar, Farafra, and Qattara to +the Mediterranean. Vertical scale 500 times the horizontal. Total +length of section about 1700 kilometres; for more than half this +distance the ground-level is seen to be above a line drawn through +the levels of the Nile in corresponding latitudes.</em> +</p> +</figure> +</div> + +<p>Can any one believe that a course of this kind was ever that of +a river? To make a through channel would entail deep cutting for +more than half the total distance of 1700 kilometres, and would +consequently involve excavating hundreds of millions of cubic +metres of rock, much of it of considerable hardness. Moreover, it +cannot be supposed, in the<span class="pagenum" id= +"Page_32">[32]</span> present state of our knowledge of the region, +that more favourable lines of communication exist and have been +overlooked. Many depressions doubtless still remain to be +discovered; but these, like those already known, will surely prove +to be merely local basins. So many cross-country journeys have now +been made in various directions through the desert, that it is +inconceivable that any continuous channel of the kind we are +discussing could possibly have escaped notice. Nor can we +reasonably suppose that recent earth-movements have produced the +present severance of the various depressions; such movements might +perhaps be invoked to account for one or two of the separating +elevations, but certainly not for all. We can therefore be +absolutely certain that neither the Nile nor any branch of it ever +passed through the Libyan Desert to the sea.<a id= +"FNanchor_11"></a><a href="#Footnote_11" class= +"fnanchor">[11]</a></p> + +<p>Even channels of tributary streams to the Nile, such as +abundantly survive in the great wadis which enter the Nile valley +on its eastern side, are markedly absent in the Libyan Desert. The +contours on the map suggest that possibly one such tributary stream +may formerly have drained the south-western faces of the great +plateau in which the depressions of Dakhla and Kharga form bays, +and have entered the Nile somewhere between Aswan and Halfa; but if +such a channel ever did exist, its actual traces have long since +been obliterated by the smoothing action of subsequent denudation, +and only the great escarpment of the plateau which it half +encircled remains to tell the tale.</p> + +<p class="ipubr2"><em>Photographs by Prince Kemal el Din, Dr. Ball, +and Mr. Walpole</em> +</p> + +<div class="figcenter iw2"> +<figure id="i01"><img src='images/i01.jpg' alt=''> +<p class="cp1">1. <em>Desert exploration with the ordinary car, +requiring help even on flat ground in sandy tracts</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i02"><img src='images/i02.jpg' alt=''> +<p class="cp1">2. <em>Caterpillar cars carrying heavy loads over a +sand-dune between Bir Terfawi and Gebel Owenat</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i03"><img src='images/i03.jpg' alt=''> +<p class="cp1">3. <em>The western wall of the Qattara depression 35 +km. S.S.W. of Qara Oasis. Top of cliff about 3 m. and floor of +depression 133 m. below sea-level</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i04"><img src='images/i04.jpg' alt=''> +<p class="cp1">4. <em>Ain el Hez, Baharia Oasis, irrigated by free +flow from well</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i05"><img src='images/i05.jpg' alt=''> +<p class="cp1">5. <em>Overlooking the Baharia depression from the +pass at its southern end: cars bound for Farafra</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i06"><img src='images/i06.jpg' alt=''> +<p class="cp1">6. <em>Northern end of Farafra depression: sandy +ravine cutting back into chalk plateau</em></p> +</figure> +</div> + +<h2><a id="s02"></a>2. <em>Origin of the Depressions.</em></h2> + +<p>It is a marked characteristic of almost all true deserts, that +they are regions of internal drainage; and the Libyan Desert is no +exception to the rule. There are a few gullies draining from the +plateau to the sea along its northern edge, and a few others +draining into the Nile Valley along its eastern border. But none of +these external drainage-lines extends for more than an +insignificant distance backward into the interior of the country. +There is, in fact, in the Libyan Desert (especially in its +north-eastern portion) a marked absence of any distinct +drainage-lines at all; in their place we find extensive stony +plains, which either slope gradually down towards the various +inland depressions, or terminate in an abrupt fall where the +depressions are cut back into them. Even in the<span class= +"pagenum" id="Page_33">[33]</span> Pluvial epoch, when Europe was +glaciated and the deep wadis of the Eastern Desert on either side +of the Nile were being cut out by great streams, there cannot have +been any external drainage from a large part of the Libyan Desert; +for if there had been, we should find the Libyan plateau far more +intensely dissected than is actually the case. The rainfall in this +region, even during the Pluvial period, must have been far smaller +than in the neighbouring tracts of the Eastern Desert and Sinai; +such rainfall as did occur was drained into the series of +depressions already described, and there either formed lakes or was +evaporated. But the action of inflowing drainage waters, carrying +sand and mud in suspension and salts in solution, is not to +<em>deepen</em> the basins into which they flow, but rather to +<em>fill them up</em>. Hence we must look to some other cause for +the formation of the basins themselves. A possible cause is to be +found in earth-movements—either a local down-folding of the crust, +or an upraising by faulting of the surrounding tracts. It is not +unlikely that such earth-movements have to some extent conditioned +the formation of the depressions; but that the depressions are not +simply faulted-down areas or subsidences is abundantly clear from +an examination of the bounding scarps and the floors of the larger +oases. Baharia is wholly, and Kharga and Dakhla are partially, +bounded by high escarpments, in many places hundreds of metres +high, and the floors of these oases are composed of the same rocks +as are exposed at the base of the bounding escarpments. It is, in +fact, obvious that these great hollows are natural +<em>excavations</em>, not subsidences. What was the excavating +agency?</p> + +<p>To the south-west of the limestone plateau which lies west of +the Nile and extends northwards from lat. 23° 30′ there is fairly +open sandstone country, and the oases of Dakhla and Kharga occupy +great bays in the escarpment which marks the south-west termination +of the plateau. It seems reasonable to suppose that the Eocene and +Cretaceous seas had their southern shores somewhere about the +latitude of Wadi Halfa, for the limestones do not extend far beyond +the tropic; and to the south the hard limestones of the plateau +probably passed gradually into softer shallow-water deposits, which +would lend themselves easily to degradation and to removal by the +agency of streams whose traces have long since disappeared. We can +thus possibly invoke water-action to account for the primitive +formation of the “bays” in which Kharga and Dakhla are situated. +But we cannot in this way explain either the further deepening of +these oases, which converted them into basins, or the excavation of +the more northerly depressions such as Baharia and Qattara.</p> + +<p>The problem as to how the excavation of the northern +depressions, and the deepening of the southern ones, were +accomplished is not altogether an easy one. There is, of course, no +doubt that wind has been the main excavating agency. All the +depressions occur in areas where soft rocks are overlain by hard +ones, and once the hard overlying rock was removed<span class= +"pagenum" id="Page_34">[34]</span> at any place, the action of the +wind on the softer beds would soon excavate a hollow. The +difficulty is only as to how the hard overlying rock was first +removed. To some who have studied the question, a sufficient +explanation is to be found in the general degradation, combined +with the tectonic disturbances—folds and faults—which are known to +have affected some of the oasis-areas, as, for instance, that of +Baharia. Given an anticlinal fold, a general lowering of the +surface by wind-degradation would eventually result in the exposure +of the soft underlying beds at the highest point of the fold, and +subsequently continued wind-erosion would proceed most rapidly on +these soft underlying rocks. Others, while admitting this +explanation as partly accounting for the formation of the +depressions, consider that other factors must have assisted to +cause penetration of the hard overlying beds, especially in the +areas where folding is not very marked.</p> + +<p>Of such other factors, I can only suggest what appears to me to +be a possible one. About twenty years ago I was mapping the +Mediterranean coastal area in the neighbourhood of Mersa Matruh, +some 160 miles to the west of Alexandria. In this area, which has +about 6 inches of rainfall in an average year, there are numerous +closed-in basins a few miles long and a few hundred yards in width, +descending to a depth of 10 metres or more in the rather soft +limestone which forms the principal rock of the locality. These +basins, though called wadis on the maps, are more usually known as +<em>’ebs</em> or “bosoms” by the local Arabs. I was at first much +puzzled to account for them; but eventually I arrived at what I +believe to be the true explanation of their formation. The basins, +of course, collect the surrounding rainfall in the winter, and the +drainage carries with it into the hollows a certain amount of fine +loam and sand from the disintegration of the surrounding surfaces. +After the rains, the bottoms of the basins become covered with +vegetation, while the surrounding rocky surfaces are left bare. In +the hot dry summer, however, the vegetation perishes, and much of +the loam is removed by the wind. We have only to assume (what seems +indeed likely) that the rootlets of the vegetation disintegrate the +limestone floors of the hollows to form fresh soil, and that more +of this is removed each year by the wind than is brought into the +hollows by the drainage, to find an adequate cause for a slow but +progressive deepening of the basins. The primitive hollow may well +be a very slight depression of the surface, such as might arise +from greater local softness of the rock and consequent more rapid +weathering. Once vegetation has commenced to grow in a slight +hollow of this kind, the action would lead to a slow yet steadily +progressive deepening year by year, and sand-erosion would tend +towards an elongation of the depression in the direction of the +prevailing wind. Can such a process as this, continued through vast +ages during which the climate was somewhat less dry than at +present, have been active in the formation of Baharia and similar +depressions?</p> + +<h2><span class="pagenum" id="Page_35">[35]</span><a id= +"s03"></a>3. <em>The Possibility of Utilization of Depressions in +the Libyan Desert for Irrigation, Drainage, or Hydraulic +Power.</em></h2> + +<p>The depression known as the Wadi Rayan, discovered by Mr. Cope +Whitehouse about 1883, situated some 40 kilometres west of the Nile +Valley and about 100 kilometres south of the latitude of Cairo, has +been so frequently described and considered in regard to its +utilization as a reservoir or as a flood-protection for Lower +Egypt, that I need say little about it beyond a reference to the +principal published works dealing with it.<a id= +"FNanchor_12"></a><a href="#Footnote_12" class="fnanchor">[12]</a> +There is no other depression in the Libyan Desert which has +received so much attention from the economic standpoint. That the +Wadi Rayan has not already been utilized as a reservoir has +depended on a variety of considerations, of which one of the +principal has been the doubts always entertained as to whether +there might not be an underground leakage from it, resulting not +only in a loss of part of the stored water, but also in damage to +the adjacent flourishing province of the Faiyum. These doubts will +not be lessened by the converging lines of evidence which I shall +bring forward in dealing with the artesian water-supplies, all +leading to the conclusion that there is an underground +water-connection between the various depressions of the Egyptian +Libyan Desert. Of late years, however, it has been proposed to make +use of the Wadi Rayan, not as a reservoir, but as a sump for +disposing of the drainage water of Upper Egypt by evaporation; and +to this, in consequence of the lower level at which the water would +stand in the depression, there is far less objection from the point +of view of possible leakage or damage to the Faiyum.</p> + +<p>The Wadi Natrun, which, though considerably less deep, is not +greatly less in extent than the Wadi Rayan, has received some +consideration as a possible sump for disposing of some of the +drainage water of the Behera Province of the Delta. So long ago as +1895 the Public Works Department studied the possibility of +draining Lake Mariut into the Wadi Natrun, and thus doing away with +the increasing cost of keeping down the level of the lake by +pumping water from it into the sea.<a id="FNanchor_13"></a><a href= +"#Footnote_13" class="fnanchor">[13]</a> The Wadi Natrun has an +area, even at the low contour of 10 metres below sea-level, of +nearly 100 square kilometres, and the average rate of evaporation +from an open water-surface within it could not well be much less +than 3 mm. per day; the wadi could therefore dispose annually of at +least 100 million cubic metres of drainage water by evaporation +alone, and probably of a considerable additional quantity by +seepage. But the<span class="pagenum" id="Page_36">[36]</span> high +cost of cutting a drainage channel from Lake Mariut to the wadi, +and the heavy maintenance charges which would be incurred in +keeping the drain open, were formidable objections to the scheme. +From a reconnaissance carried out in 1896, Mr. Verschoyle found +that the length of the proposed drain would have to be almost 80 +kilometres, and for the greater part of the way it would have to be +a cutting 20 metres in depth through desert and ridges of drifting +sand; he remarked that if it were an easy matter to make the +connection, it would be no easy matter to maintain it; and he +concluded that the scheme was an impracticable one.<a id= +"FNanchor_14"></a><a href="#Footnote_14" class="fnanchor">[14]</a> +A more recent proposal has been to construct a partly tunnelled +channel instead of an open drain; but this has likewise been found +to be impracticable, as involving too heavy an outlay for the +benefits which would result.<a id="FNanchor_15"></a><a href= +"#Footnote_15" class="fnanchor">[15]</a></p> + +<div class="figcenter iw2"> +<figure id="i07"><img src='images/i07.jpg' alt=''> +<p class="cp1">7. <em>Qasr Farafra, seen from the north over plain +of powdery chalk forming floor of depression</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i08"><img src='images/i08.jpg' alt=''> +<p class="cp1">8. <em>Escarpment and “Hattia” of Abu Mungar from +the south</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i09"><img src='images/i09.jpg' alt=''> +<p class="cp1">9. <em>The “Hattia” of Abu Mungar from the east: +well on earth-mound on right</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i10"><img src='images/i10.jpg' alt=''> +<p class="cp1">10. <em>The principal well at Qasr Farafra</em></p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i11"><img src='images/i11.jpg' alt=''> +<p class="cp1">11. <em>A street in Qasr Farafra, with irrigation +canal</em></p> +</figure> +</div> + +<p>When the great extent and depth of the Qattara depression were +established by Mr. Walpole’s explorations of last year, hopes were +immediately entertained that the depression might be made to serve +some useful economic purpose. Any idea of its being of use as a +Nile reservoir was of course at once cut out, not only by reason of +its position and distance from the Nile, but also by its immense +size; for even if we could turn the whole Nile flood into it, some +twenty years or more would be occupied in filling it to a +sufficiently high level,<a id="FNanchor_16"></a><a href= +"#Footnote_16" class="fnanchor">[16]</a> and the loss by +evaporation from so large an area would be enormous. As a +receptacle for drainage water from the Delta it appeared equally +impossible of consideration, because of the great length and depth +of the channels which would have to be cut to reach it. A more +reasonable prospect seemed to be that of admitting sea-water from +the Mediterranean into it by means of a navigable canal from the +Arabs Gulf; this would only have to be about 56 kilometres in +length to reach the nearest point of the depression; and once the +canal was made and the depression filled, ships might sail almost +to Siwa. Other advantages which might accrue from the formation of +this inland sea were an increased humidity of the climate along the +Mediterranean Littoral of Egypt, leading to increased rain-crops in +that region, the establishment of a valuable fishery, and a +possible increase in the water-supply of the oases by the causing +of a<span class="pagenum" id="Page_37">[37]</span> slight rise in +the static water-level there. Another idea, which rapidly followed +the first one, was to utilize the depression as a source of +electrical power for driving pumps by which the drainage of the +northern parts of the Nile Delta might be improved. At first sight +this latter prospect looked a very attractive one. The salt-marsh +which covers much of the floor of the depression appeared +suggestive of a former sea-connection, and if we could trace out +this old connection, the cutting of a canal along it might not, it +was thought, be a very expensive matter. Moreover, it was apparent +that evaporation from an inland sea or lake of so large an area +would keep pace with quite a large influx from the Mediterranean, +so that if the influx were restricted to such a quantity as would +permit of the lake-surface being maintained at a level considerably +below that of the Mediterranean, power could be generated +continuously. Suppose, for instance, that we maintained a permanent +water-level in the lake of 50 metres below the sea; the estimated +area of the lake at this level being 9000 square kilometres and the +mean evaporation assumed to be 4 millimetres a day, an influx of no +less than 36 million cubic metres of water per day could be passed +into the lake without altering its level, and this with a fall of +50 metres would suffice theoretically for the continuous generation +of over 270,000 horse-power. Of course the lake would gradually get +more and more saline, but the power might continue to be maintained +for very many years before the lake became as rich in salt as the +Dead Sea.</p> + +<p>But alas! an investigation of the northern borders of the +depression showed that the hoped-for traces of a former connection +with the Mediterranean Sea do not exist. The depression is entirely +shut in from the north, either by great cliffs, or by ground lying +so high that the cutting of a canal to the sea is utterly +impracticable. Of the 56½ kilometres from the sea-level contour of +the depression to the coast along a line running 12° east of north +from Moghara Lake (which is the easiest line hitherto found for the +cutting of a canal), only 16 kilometres are at less than 50 metres +above sea; 31 kilometres lie at altitudes between 50 and 100 +metres; and 9½ kilometres are above the 100-metre level. An open +channel being thus put out of the question, it was next natural to +inquire whether a tunnel, or a channel partly open and partly +tunnelled, could be excavated to serve for the conveyance of +sea-water into the depression. But even this, though perhaps not +impracticable, would be a very costly undertaking. The conveyance +of the requisite quantity of water, even at a relatively high +velocity (which of course implies a considerable slope), would +necessitate a tunnel or tunnels of very large dimensions. To convey +36 million cubic metres a day at a velocity of 5 kilometres per +hour would require a sectional area of 300 square +metres—<em>i.e.</em> if two tunnels were made, each would have to +be 14 metres in diameter. The cost of boring and lining such +tunnels would certainly be very great, and it is doubtful whether +the value of the power generated could justify the capital +expenditure<span class="pagenum" id="Page_38">[38]</span> involved +in the excavation and other works which would be necessary. Until +more is known of the nature of the strata through which the +aqueduct would have to pass, and as to the length of tunnelling and +amount of open cutting which would be required, it is impossible to +form even an approximate estimate of the expense which the +undertaking would involve. All that can be said at present is that +the utilization of the Qattara Depression offers a possible means +of obtaining power on a large scale for the drainage of the +low-lying lands of the Delta, with at the same time a prospect of +improving in some measure the agricultural resources of the +Mediterranean Littoral; much further investigation will have to be +accomplished before any judgment can be formed as to whether such a +project would be an economically sound one.</p> + +<p>In formulating any scheme for improving the drainage of the +Delta, it is of course important to consider, not only the manner +in which the drainage water could be ultimately disposed of, but +also the modifications which would have to be made in the existing +drains and irrigation canals—modifications which would need to be +carried out without serious interruption to existing agriculture. A +scheme which otherwise appeared attractive might easily prove to be +impracticable by reason of the heavy expenses and inconveniences of +the subsidiary works which would be required to make it +effective.</p> + +<div class="figcenter iw3"> +<figure id="map2"> +<p class="cpm">THE LIBYAN DESERT<br> +Showing Surface-Relief, Contours of Static Underground +Water-levels,<br> +Distribution of Sand-dunes, and Routes of Principal Exploratory +Expeditions in the West and South<br> +by<br> +Dr. JOHN BALL</p> + +<p class="ipubr">THE GEOGRAPHICAL JOURNAL JULY 1927</p> +<a href="images/map2_large.jpg"><img src='images/map2.jpg' alt= +''></a> +</figure> +</div> + +<h2><span class="pagenum" id="Page_105">[No. 2<br> +105]</span><a id="s04"></a>4. <em>The Artesian Water +Supplies.</em></h2> + +<p>The origin of the artesian water supplies of the Egyptian oases +of Baharia, Kharga, Dakhla, and Farafra (Siwa seems hitherto +generally to have been left out of consideration) has been a +much-discussed question. Some geologists, myself amongst them, have +always regarded the water as being derived from rainfall in the +western Sudan, flowing underground in permeable beds towards the +Mediterranean. Others have held the view that the oasis waters are +merely Nile water which has penetrated more or less laterally into +the adjoining deserts. The arguments that have been urged in +support of the former view are, firstly, the high temperature of +the water in many of the oasis wells; and, secondly, that the +levels of the springs and wells are often much higher than those of +the Nile in the same latitudes. To these arguments it has been +justly replied that neither of them is conclusive; the high +temperature of the outflowing water merely testifies that it has +descended to considerable depths at some part of its underground +path not very remote from the point of outflow, but really tells us +nothing as to its place of origin; and the high level of the +springs in Baharia, for instance, as compared with that of the Nile +in the same latitude, might be accounted for by the seepage from +the Nile taking place fairly high up in the river’s course. There +the question remained until 1925, when I was able to visit and +determine the positions and levels of a number of water-sources +farther in the interior than any of those on which the “Nile” +argument was based. Amongst other level-determinations, I +ascertained that the Sheb well is 228 metres above sea-level, and +that Merga Lake, lying far to the south-west (in lat. 19° 3′, long. +26° 18′), is at an altitude of no less than 509 metres above the +sea. Shortly before my tour in the Sudan, Hassanein Bey had +confirmed Rohlfs’ level of 400 metres for the Kufra water-sources, +and I had found that of Abu Mungar (north-west of Dakhla Oasis) to +be 117 metres. At all these places the water-supplies are derived +from underground sources in the same rock—namely, the Nubian +sandstone, which covers such vast areas in the Sudan and Egypt.</p> + +<p>I had thus four well-determined natural water-levels at the +corners of a great quadrilateral whose sides averaged over 500 +kilometres in length, and embraced more than 20 square degrees of +the Earth’s surface. Now just as in solid geometry the levels of +any three points determine the inclination of an oblique plane to +the horizontal, so on the Earth any three levels will determine the +inclination of a surface to the geoid (of course assuming both +geoid and surface to have the same curvature).<span class="pagenum" +id="Page_106">[106]</span> And on making the calculation, I found +that I obtained practically the same degree and direction of +inclination for the natural water-surface, whichever three of the +four known points I utilized for the calculation. In other words, I +found that if I took, say, the levels of Kufra, Abu Mungar, and +Sheb, and deduced from them the inclination of the water-surface to +the horizontal, I could <em>calculate</em> the level of Merga +pretty exactly. Extending the trial, I found that I could do the +same with a fairly close approximation for the other wells in the +Sheb neighbourhood, and also for wells in the oases of Dakhla and +Kharga. The conclusion seemed irresistible that all the wells +considered were fed from a continuous sheet of underground water; +and it was evident that this water did not come from the Nile, +firstly because of the high level of Merga, which is above that of +the swamps of the Bahr el Ghazal and other western feeders of the +White Nile, and secondly because of the direction of the downward +slope of the underground static water-surface, which is from the +south-west, instead of from the south as it would have been had the +water been derived from the Nile in the Bahr el Ghazal region. The +true source of the water must be somewhere more or less nearly on a +line drawn south-west from Dakhla, for this is the direction of +upward slope of the underground static water-surface; and if such a +line be drawn on a map of Africa, it will be found to lead towards +the Erdi and Ennedi region, on the borders of the Chad basin. It is +in the highlands of Eastern Erdi and Ennedi, therefore, that we +must look for the source of the artesian water of the Egyptian +oases. What is known of this region from the recent explorations of +Colonel Tilho lends good support to our conclusion.<a id= +"FNanchor_17"></a><a href="#Footnote_17" class="fnanchor">[17]</a> +It is a bare and rugged sandstone country, where, in spite of a +rainfall which is by no means negligible, permanent water-sources +are scanty, and where, in consequence, there must be a considerable +absorption of moisture by the rocks; and it lies at so high an +altitude as to give sufficient “head” for the absorbed water to +percolate through the porous sandstones and thus to reach +Egypt.</p> + +<p>Being convinced that I had at last arrived at the true origin of +the artesian water, I next began to entertain the idea of +attempting to make a map which would show the contours of the +underground water-sheet, and from which, in conjunction with the +contour-map of the surface which I had already prepared, I might be +able to predict the depth of boring required to tap the underground +water at any point in the desert. But a little consideration showed +that this idea was an impracticable one, by reason of our ignorance +of the underground geological structure over the greater part of +the desert. The underground water would naturally pass along +permeable sandstone beds, often confined between impermeable clays +above and below. And although the general structure of the Libyan +Desert is doubtless one of simplicity as compared with that of +other parts of Egypt, yet we know, from observations in the oases +and<span class="pagenum" id="Page_107">[107]</span> in the Owenat +region, that the beds are in some places folded and faulted, and +that in others they have been uplifted and entirely removed by +denudation, with the exposure of large areas of the underlying +ancient crystalline rocks. The only parts of the desert for which +the boring-depths could safely be predicted would be certain small +areas within the oases, where wells have been sunk in sufficient +numbers to give us definite information as to the local underground +structure; and underground-water maps of these small areas, though +they might usefully systematize our knowledge concerning them, +would not be of any use for predictions at points situated +elsewhere in the deserts.</p> + +<p>But while it was thus impracticable to prepare maps showing +everywhere the depth at which underground water actually exists, I +conceived that it might be quite possible to prepare maps showing +<em>static water-levels</em>; that is, the levels to which the +water would anywhere rise hydrostatically when once it <em>was</em> +tapped by borings. For the slope of the static water-surface +between known points will be largely independent of the underground +structure of the intervening country. Apart from any physical +changes which may still be going on in the underground rocks +themselves through geological agencies—changes which, if taking +place at all, must be so slow as to be negligible except in the +course of centuries—the only factors which can affect the slope of +the static water-surface, once it has been established, are +variations either in the rate of supply of water to the beds, or in +the rate at which it is removed from them. As regards variations in +the rate of supply, it is obvious that variations in the annual +rainfall of the Erdi and Ennedi region must cause very considerable +variations from year to year in the amount of water received by the +underground beds. But the resistance of friction to the flow of +water through the pores of the sandstones is so great, that the +annual oscillations of pressure must be rapidly damped out as the +distance from the place of influx increases; consequently the +levels of the water in the wells of the Egyptian oases (and even, +so far as is known, that of the lake at Merga) show little or no +annual variation. And with regard to variations in the rate of +removal of water from the beds (by outflow to the Nile, or to the +sea, or into lakes wherein it evaporates, or by the exploitation of +wells and springs for irrigation purposes), these changes, though +possibly in some cases they may be progressive, and in restricted +localities very sensible, can exercise but little influence from +year to year on the general distribution of water-pressure within +the underground strata. We may therefore conclude that the gradient +of the static water-surface will everywhere have assumed +practically a steady state. Unlike the actual water bearing beds +themselves, which may be much folded, the static water-surface will +in general have simple gentle slopes everywhere in the open desert. +In the oases, of course, where numbers of wells yielding large +outputs have been bored in proximity to each other, the static +water surface will be wrinkled; but over the vast bulk of the +desert the<span class="pagenum" id="Page_108">[108]</span> contours +may be expected to be smooth curves. The diagrammatic section below +will, I think, make clear this point about the general +non-dependence of the shape of the static water-surface on the +geological structure:</p> + +<div class="figcenter iw2"> +<figure id="map3"><a href='images/map3.jpg'><img src= +'images/map3.jpg' alt=''></a> +<p class="cp2"><em>Diagrammatic section showing that the static +water-level is largely independent of the underground +structure</em> +</p> +</figure> +</div> + +<p>In the diagram, FEKHG represents a water-conveying stratum, +folded throughout its course and faulted at HK, but having a +general downward slope from F to G. A and B represent points at +which the water just rises to the ground-level, either through +natural fissures or in artificial borings. The straight line drawn +through A and B represents very approximately the static level at +any point between A and B, that is, the level to which the water +would rise in bores carried down to the water-bearing bed. A boring +at C, for instance, would have to go down to E to tap the water, +but once the bed was tapped the water would rise in the bore as far +as D. At the fault HK, the pressure of the water at K will cause it +to rise through the crushed rock at the fault-plane and re-enter +the porous stratum at H. If there is a considerable outflow at B, +and the fault-plane is a very narrow fissure, we may expect some +drop in the line AB over the fault, by reason of the extra +frictional absorption of head at this place. But unless the +thickness and degree of permeability of the fault-rock are markedly +different from those of the sandstone bed itself, the drop of +pressure will not greatly disturb the general slope AB. In any case +it is apparent that the level of the static water-surface at any +place between A and B is capable of being estimated with a far +closer degree of approximation than is the level of the water-sheet +itself. We may therefore justifiably assume a uniform gradient for +the static level between points at which that level is known, +disregarding folds in the strata; and though we cannot entirely +allow in detail for unknown faults and variations in permeability, +it must be borne in mind that the <em>total</em> effect of all the +unknown factors between any two known points is already +automatically allowed for in our data. It is only the variations +from uniformity, due to the unknown distribution of the faults and +of the departures from the average permeability, which can affect +us; and these variations and departures are probably but small in +most of the great unexplored areas of the south-west of Egypt, +where the geological structure, from all we know of it, appears +generally to be remarkably uniform.</p> + +<p>The first requisite for the construction of a map showing the +contours of the static water-surface was, of course, a sufficiency +of well-determined<span class="pagenum" id="Page_109">[109]</span> +positions of points where the static water-level of the artesian +supply was fairly exactly known. Such points are the springs and +wells of the various oases, the surfaces of lakes occupying +depressions and presumably fed by underground supplies, and any +places on the Nile where the river taps artesian beds.</p> + +<p>In regard to the wells and springs, it was obvious that only +those known to derive their supplies from artesian sources could be +utilized as giving points on the static water-surface. This +consideration cut out from the discussion the springs of Owenat and +Arkenu, which are known to be fed by local rainfall, and also the +small water-sources of Kurkur, Dungul, Nakheil, and Ain Amur, which +occur in situations where percolation from occasional local +rainfall seems to be the only possible source of supply. And for +reasons which will appear presently, none of the wells and springs +situated to the north of the Siwa-Qattara-Faiyum chain of +depressions could be considered as entering into the problem. With +these exceptions, every water-source situated within the area of +the Libyan Desert covered by the map, and whose level was known, +was utilized; but in the greater oases and in the Wadi Natrun the +wells and springs are so numerous and so close together that in +these localities it was necessary to select one or two wells as +representatives of a group. I had no hesitation in including the +wells of Siwa and the Wadi Natrun, because the temperature of some +of the wells and springs of Siwa, and the quantity of the output of +water at both places, seem to me to afford conclusive evidence of +the artesian character of their supply.<a id= +"FNanchor_18"></a><a href="#Footnote_18" class="fnanchor">[18]</a> +The wells of the little oasis of Lageita, to the east of the Nile +near Qena, were included, for although they are not in the Libyan +Desert, they most probably derive their supplies from the same +underground flow which feeds the western oases. I have included +only one well in which the water does not rise nearly to the +ground-level. That well is one which was bored by the British Army +during the Great War, at a place called B6, some 40 kilometres to +the east of Baharia Oasis. The level of the ground at this point is +112 metres above sea-level, and as the water was stationary in the +bore at 78 metres below the ground, the static level here is 34 +metres above sea.<a id="FNanchor_19"></a><a href="#Footnote_19" +class="fnanchor">[19]</a> The well is said to have yielded some 800 +gallons per hour without the water-level in the bore being sensibly +changed.</p> + +<p>The level of the well at Sarra has recently been determined by +Prince<span class="pagenum" id="Page_110">[110]</span> Kemal el +Din; but I have not included it in my data, because he informs me +that the water-level fluctuates by 20 metres or more in different +years, while the level of the artesian water of the Egyptian oases +and Merga is very nearly constant. The inference I draw from the +great fluctuations in the water-level at the Sarra well is that it +is dependent on percolation from a more or less local rainfall +rather than on the same flow which feeds the Egyptian oases.</p> + +<h2><a id="s05"></a>5. <em>Permanence of Lakes.</em></h2> + +<p>In regard to lakes and salt-marshes, the permanence of those +occupying the depressions of Areg, Bahrein, Sittra, and Qattara can +only, I think, be adequately explained by regarding them as fed, at +least in part, by underground supplies coming into them from the +south. The total area of the lakes of Bahrein, Nuemisa, Sittra, and +Moghara is nearly 20 square kilometres, and that of the +salt-marshes (<em>sabakha</em>) is not less than 5000 square +kilometres. The depressions are situated in a region which is +nearly rainless; in Siwa the mean annual rainfall is only about a +quarter of an inch, and that in the depressions farther south, such +as Bahrein and Sittra, is doubtless even smaller. The mean daily +evaporation from the lake-surfaces cannot well be less than some 4 +mm., which would mean a lowering of the lake-levels by evaporation +of 1½ metres each year unless there was some inflow to make up for +the loss. And though the rate of evaporation from the salt-marshes, +area for area, is doubtless very much smaller than that of the +lakes, the 250-fold greater extent of the marshes makes it certain +that the total quantity of water annually evaporated from them must +far exceed that from the lakes.</p> + +<p>It appears unlikely that the loss by evaporation in the lakes +and marshes can be entirely made up from local rainfall and by +seepages from the northern slopes. The rocks forming the surface of +the great Miocene plateau, 200 metres high, which separates the +depressions from the sea, are chiefly limestones and clays; the +beds are nearly horizontal, but such slight dips as exist are +believed to be towards the sea. The average annual rainfall on the +coastal portion of the plateau is about 6 inches; but it falls off +rapidly inland, till it is only about a quarter of an inch near +Siwa. The heaviest rainfall on the plateau thus occurs along a +strip parallel to the coast, where it is largely drained off +towards the sea by the gullies which indent the plateau-edge. Of +that which falls on the plateau-surface farther inland +comparatively little is absorbed, owing to the generally non-porous +nature of the uppermost rocks; after a heavy shower, water lies on +the surface in shallow pools for a few days and is soon evaporated. +So impervious to water is the limestone in this region, that the +Romans excavated chambers in it to form reservoirs, of which many +hundreds still exist. Nor can we think that much surface +drainage-water from the country to the south ever finds its way +into the depressions; for there is an almost complete absence of +drainage-lines entering them.<span class="pagenum" id= +"Page_111">[111]</span> At the feet of the northern scarps of the +Qattara depression, and along the north-eastern shores of the lakes +in the Wadi Natrun, there are, indeed, small springs which show +that some of the rain falling on the plateau does actually +penetrate the rocks and escape by seepage into the depressions. But +the amount of this seepage appears to be insignificant compared +with the volume of water which must annually disappear from the +lakes and marshes by evaporation. A further consideration bearing +on this point is that whatever may have been the agency by which +the depression of Siwa was formed, that same agency almost +certainly operated to produce the other depressions of the northern +chain; and it seems most unlikely that a connection should have +been opened up with the underground water-bearing beds in Siwa, and +not also in the larger and much deeper depression of Qattara.</p> + +<p>It would be a difficult matter to estimate the relative +proportion of the water entering the depressions by underground +flow from the south, to that contributed by local rainfall and +seepage from the northern slopes. But that is not necessary for our +immediate purpose. It is sufficient to show that there must be +<em>some</em> influx into the depressions from the same source as +that which supplies the wells of the greater oases, to establish +the existence of that underground water-connection which is all +that we need to justify us in regarding the levels of the lakes and +salt-marshes as furnishing us with points on the static +water-surface; and from the considerations mentioned above it seems +to me certain that some influx of underground water really does +take place.</p> + +<p>I have also thought it justifiable to include the Birket el +Qarun in my collection of static water-level data, because although +that lake was probably first formed by an overflow of the Nile into +the Faiyum, and is even now being fed by Nile water through the +Faiyum drains at the rate of some 350 million tons a year, there is +a certain amount of evidence suggesting that it has some +underground water-connection with the Qattara depression. That +evidence, to which attention was first drawn by Professor +Schweinfurth,<a id="FNanchor_20"></a><a href="#Footnote_20" class= +"fnanchor">[20]</a> consists in the relatively low salinity (1·3 +per cent.) of the lake, notwithstanding the long period through +which it has been subject to evaporation and the fact of its having +shrunk to dimensions very much smaller than it possessed in ancient +times. Unless there has been a large underground efflux of salt +water from the lake, it appears impossible to account for its +present degree of freshness. In Professor Schweinfurth’s day, of +course, the existence of the Qattara depression was unknown, and it +was puzzling to suggest where the salt water had gone to.<a id= +"FNanchor_21"></a><a href="#Footnote_21" class="fnanchor">[21]</a> +An underground leakage from the Birket el Qarun into the Qattara +depression is quite conceivable, for although the two places +are<span class="pagenum" id="Page_112">[112]</span> separated by +some 200 kilometres, there is a very considerable fall between +them. Thus the salt in the marshes of the Qattara depression may +possibly have come in part from the Birket el Qarun. The present +rate of discharge of the Faiyum drains into the lake is, however, +just sufficient to make up for an average daily evaporation from +the lake-surface of a little over 4 mm., which is about the rate we +might expect; and although the level of the lake-surface has fallen +some 5 metres since observations of it were first made in 1886, it +is now nearly stationary; hence it does not appear likely that +there is much underground leakage at present. If the former leakage +from the lake took place by lateral flow into porous strata near +its surface, of course the leakage may have been arrested by the +lowering of the lake-level uncovering the porous beds into which it +took place; but I think a more likely explanation is that the +leakage occurred at or near the bed of the lake, and has gradually +been reduced by the continued deposition of Nile mud on the +lake-bottom, and by the diminution of head due to the fall in the +water-level.</p> + +<p>In regard to the tapping of the artesian waters by the Nile, +there is only one locality in which this is known to take place; +but the quantity of underground water which is there withdrawn by +the river is probably very considerable. When I was surveying the +Nile Valley between Aswan and Korosko in December 1898, I observed +that in the vicinity of the temple of Dakka (about 105 kilometres +south of Aswan) the lands on the west bank of the river were being +irrigated with warm water, drawn by “sakias” (water-raising +machines) from pits sunk in the alluvial flat which extends between +the river and the edge of the sandstone desert. The length of the +tract over which the warm water was being withdrawn for irrigation +was found to be about 16 kilometres, stretching from 2 kilometres +north of Dakka temple southwards to the temple of Maharraga; and +the width of the alluvial tract at Dakka, where it is widest, was +about 1300 metres. Some of the water-pits were more than a +kilometre from the river. Levelling from the Nile (the surface of +which was then about 99 metres above sea) across the cultivation to +one of the sakia-pits 750 metres west of the river, I found the +level of the ground at the sakia-pit to be 7·9 metres above that of +the Nile, and the water-surface in the pit to be 8·4 metres below +the ground-level; there was 1·2 metres depth of water in the pit. +The temperature of the water in the pit I found to be 83° F., while +that of the Nile was 60° F. and that of the air was 67° F. The +headman of Dakka told me that the exploitation of this warm +underground water had begun about 1887; they dig out the sandy mud, +and then see the water oozing rapidly into the pit out of the +sandstone below. On crossing to the east bank of the river, I found +that there also the warm water was being similarly raised for +irrigation, though to a smaller extent, because on that side the +sandstone desert approaches more closely to the river and there is +much less cultivable land. The exploitation of the water on the +east side of the Nile extended only over<span class="pagenum" id= +"Page_113">[113]</span> a distance of about 5 kilometres along the +bank, with a maximum width of alluvial plain of 600 metres, just at +the place where the great Wadi Alagi debouches into the Nile +Valley. As the sandstone bed from which the warm water issues is +less than 2 metres below the level of the water-surface of the +Nile, and the water occurs on both sides of the river, it is +certain that the water-bearing bed is cut through by the Nile +channel itself; the seepage into the river along the stretch of 16 +kilometres must therefore be very considerable. It seems evident +that the water is not derived from the bed of the Wadi Alagi, great +drainage-channel though that wadi is; for we could not then account +for the temperature of the water, nor for its appearing to a larger +extent on the west bank than on the east, with the river in +between. Moreover, the water appeared to be much more free from +salts than we should expect it to be if it were merely drainage +from the Wadi Alagi. It strongly resembles, in fact, both in +temperature and character, the artesian water of the greater oases, +and there can hardly be the smallest doubt that at Dakka the Nile +is not only continually abstracting artesian water from the same +underground water-sheet that feeds the oases, but is abstracting it +in far larger quantities than those yielded by all the oasis wells +and springs put together.<a id="FNanchor_22"></a><a href= +"#Footnote_22" class="fnanchor">[22]</a> It is certainly remarkable +that the place where considerable supplies of warm underground +water enter the Nile should coincide with the embouchure of what is +perhaps the greatest drainage channel of the Eastern Desert of +Egypt; but I think it is likely that the explanation of the +coincidence may be a tectonic one; the water-bearing beds may have +been brought up by a local fold in the strata, and the same fold +may in some way have conditioned the formation of the primitive +drainage-line which was ultimately to become the Wadi Alagi.</p> + +<p>Having now indicated briefly the grounds for their acceptance, I +give below a table showing the various points which I have adopted +as furnishing data for constructing the contours of the static +water-surface underlying the Libyan Desert, together with the +altitudes of the points above or below sea, and the sources of +these level-data. The levels are doubtless in some cases slightly +inaccurate; but a few metres of error are immaterial to the object +in view, and it is believed that even those levels which rest on +barometric determinations are sufficiently accurate for our +purpose.</p> + +<table class="tless" id="t114"> +<tr> +<th colspan="3" class="sc"><span class="pagenum" id= +"Page_114">[114]</span>List of Adopted Points on the Static +Water-Surface</th> +</tr> + +<tr> +<th><em>Place.</em> +</th> +<th><em>Level (metres).</em> +</th> +<th><em>Determined by.</em> +</th> +</tr> + +<tr> +<td class="tdl-top hang1">Wadi Natrun, surface of lakes</td> +<td class="tdl-bot pad15">− 23</td> +<td class="tdl-bot hang1">Ball, Trigonometric levelling, 1914.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Birket el Qarun, surface of lake</td> +<td class="tdl-bot pad15">− 45</td> +<td class="tdl-bot hang1">Survey of Egypt, 1926. Based on spirit +levelling from Alexandria.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Moghara, surface of lake</td> +<td class="tdl-bot pad15">− 23</td> +<td class="tdl-bot hang1">Walpole, Trigonometric levelling, +1924.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Qattara Depression, various points on +salt-marsh, the lowest being</td> +<td class="tdl-bot pad15">− 80<a id="FNanchor_23"></a><a href= +"#Footnote_23" class="fnanchor">[23]</a></td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Sittra, surface of lake</td> +<td class="tdl-bot pad15">− 16</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Areg, surface of lake</td> +<td class="tdl-bot pad15">− 25</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Siwa</td> +<td class="tdl-bot pad15">− 17</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Jaghbub</td> +<td class="tdl-bot pad15">+ 32</td> +<td class="tdl-bot hang1">Hassanein, Barometric observations, +1923.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Jalo</td> +<td class="tdl-bot pad15">+ 61</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Butaffal</td> +<td class="tdl-bot pad15">+ 98</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">El Harrash</td> +<td class="tdl-bot pad15">+ 310</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Awadel (Kufra Oasis)</td> +<td class="tdl-bot pad15">+ 434</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Ezeila (Kufra Oasis)</td> +<td class="tdl-bot pad15">+ 389</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bawitti (Baharia Oasis)</td> +<td class="tdl-bot pad15">+ 129</td> +<td class="tdl-bot hang1">Ball, 1917, and Walpole, 1924. +Trigonometric levelling.</td> +</tr> + +<tr> +<td class="tdl-top hang1">El Hez (Baharia Oasis)</td> +<td class="tdl-bot pad15">+ 134</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">B6 Well (water surface in)</td> +<td class="tdl-bot pad15">+ 34</td> +<td class="tdl-bot hang1">Walpole, Trigonometric levelling, 1924, +and military records of depth, 1916.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Lageita (Eastern Desert)</td> +<td class="tdl-bot pad15">+ 121</td> +<td class="tdl-bot hang1">Murray, Trigonometric levelling, +1921.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Farafra</td> +<td class="tdl-bot pad15">+ 90</td> +<td class="tdl-bot hang1">Ball, Barometric observations, 1924.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Abu Mungar</td> +<td class="tdl-bot pad15">+ 117</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Mut (Dakhla Oasis)</td> +<td class="tdl-bot pad15">+ 119</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Kharga (average of numerous wells)</td> +<td class="tdl-bot pad15">+ 70</td> +<td class="tdl-bot hang1">Beadnell, Spirit levelling, 1909.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Ain Ismail (Kharga Oasis)</td> +<td class="tdl-bot pad15">+ 67</td> +<td class="tdl-bot hang1">Ball, Barometric observations, 1925.</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Murr</td> +<td class="tdl-bot pad15">+ 156</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Abu Hussein</td> +<td class="tdl-bot pad15">+ 182</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Kassaba</td> +<td class="tdl-bot pad15">+ 176</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Sheb Well</td> +<td class="tdl-bot pad15">+ 228</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Safsaf</td> +<td class="tdl-bot pad15">+ 230</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Terfawi</td> +<td class="tdl-bot pad15">+ 244</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Merga, surface of lake</td> +<td class="tdl-bot pad15">+ 509</td> +<td class="tdc-bot word-spaced2em">„ „ „</td> +</tr> + +<tr> +<td class="tdl-top hang1">Dakka, water-surface in wells</td> +<td class="tdl-bot pad15">+ 99</td> +<td class="tdl-bot hang1">Ball, Spirit levelling from the Nile, +1898.</td> +</tr> +</table> + +<p>To prepare a map showing the contours of the static +water-surface, I took a graticuled sheet and plotted the +above-scheduled points on it in their ascertained geographical +positions, affixing the adopted level to each. To get points on the +various contours at vertical intervals of 100 metres, I joined each +pair of points on the map by a pencil line, and then, by +interpolation from the terminal levels, found the points on this +line<span class="pagenum" id="Page_115">[115]</span> where the +various contours crossed it, on the assumption of a uniform +gradient between the terminal points. Many of the lines thus drawn +of course crossed each other, so that interpolation of the static +level at the point of their intersection gave two values for the +same place. But their agreement was wonderfully close, considering +the fewness and the scattered nature of the datum-points, and this +went a long way to encourage me in the belief that the hypothesis +on which I had been working, namely, that of an underground +water-connection between all the points included in my list, was +correct. I found that the contours of the static water-surface +could be approximately represented by a series of smooth curves, as +shown (on a reduced scale) in the outline map below.</p> + +<p>Apart from the general smoothness of the curves, especially in +the south-west, where it may in part be due to the scantiness of +control-points, the most striking thing on this outline map is the +north-eastward projection of the 100-metre static contour, where it +runs out so as to include Baharia Oasis. The reasons for this +projection are obviously the efflux of water, on the one hand +north-westwards into the great Qattara depression, and on the other +hand into the Nile at Dakka. The indentation of the 400-metre +contour near Kufra is likewise explained by the withdrawal of water +from the wells of that oasis. The general parallelism of the curves +in the south-western part of the map, showing a gradual rise in a +south-westerly direction towards the Erdi and Ennedi country +(which, as I have already stated, is the most probable source of +the underground water) is strikingly apparent. I have not been able +to extend the contours far to the east and west of Merga, for lack +of control-points. It is much to be hoped that some future +traveller will determine the water-levels at Selima and Lagia, +which would enable the static contours to be extended into the +region between Merga and Dongola; provided, of course, that an +examination of the water-sources at these places proves their +supplies to be artesian.</p> + +<p>The most effective way of testing any working hypothesis in +natural science being the prediction of hitherto unobserved facts, +I venture to forecast that if, as is most likely, the water-sources +of Selima and Lagia are artesian, their levels when eventually +determined will not be found to differ very much from 270 and 390 +metres above sea respectively. These are the approximate levels +deduced by prolonging the static water-contours of my maps into the +localities of these wells, assuming the contours to continue as +smooth curves.</p> + +<div class="figcenter iw3"> +<figure id="map4"><a href='images/map4.jpg'><img src= +'images/map4.jpg' alt=''></a> +<p class="cp2"><em>Outline map of the Libyan Desert, showing the +points where the static water-levels are known, and the deduced +contours of the underground static water-surface, on the hypothesis +of a continuous hydraulic connection between the points</em> +</p> +</figure> +</div> + +<p>Another interesting prognostication which I think may fairly be +deduced from the map is that if ever the well at Sarra is +considerably deepened, a much more abundant water-supply will +probably be obtainable. The ground-level at Sarra, according to +observations made by Prince Kemal el Din, is 461 metres above sea, +and the water-level in the well varies in different years from +about 390 to about 410 metres above sea. But an examination of the +static contours of the map shows that<span class="pagenum" id= +"Page_116">[116]</span> the static level of the true artesian water +in the neighbourhood of the well is probably somewhere about 500 +metres above sea, though an exact estimation of the static level at +that spot is not possible because of the lack of data farther west. +As already remarked on <a href="#Page_110">p. 110,</a> I think +the<span class="pagenum" id="Page_117">[117]</span> present supply +at Sarra is derived from more or less local rainfall, conveyed by +higher-lying permeable strata than those which convey the main +artesian supplies of Kufra and the Egyptian oases; by deepening the +well considerably, lower-lying beds might be reached so as to tap +the main supply, and the water might even be expected to overflow +at the surface.</p> + +<p>Interesting as are the static water-level contours in +themselves, they become vastly more so when superposed on the +ground-contours, as is done in the larger map (<em>G.J.</em>, July, +following <a href="#map2">p. 96</a>). From the two sets of contours +on that map we can estimate at any point the approximate depth of +the static water-level below the ground; and this information +affords new light on some of the most interesting, but hitherto the +most difficult, of the problems connected with the Libyan +Desert.</p> + +<div class="figcenter iw1"> +<figure id="i12"><img src='images/i12.jpg' alt=''> +<p class="cp1"><em>Pottery Hill, possible site of “Zerzura,” from +the south-west</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i13"><img src='images/i13.jpg' alt=''> +<p class="cp1"><em>Bir Kassaba, a watering-place on the Darb el +Arba’in</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i14"><img src='images/i14.jpg' alt=''> +<p class="cp1"><em>The waterless stretch of the Darb el Arba’in +between Bir Murr and Kharga</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i15"><img src='images/i15.jpg' alt=''> +<p class="cp1"><em>Bir Sheb, a well on the Darb el Ar ba’in</em> +</p> +</figure> +</div> + +<h2><a id="s06"></a>6. <em>Can the Present Water-supplies of the +Mediterranean Littoral be supplemented by Artesian +Borings?</em></h2> + +<p>The present water-supplies of the Egyptian portion of the +Mediterranean littoral, derived mainly from shallow wells dependent +on the local rainfall, are neither very abundant nor of very good +quality. At one or two of the most important settlements along the +coast, such as Matruh and Sollum, attempts have been made to +improve the supplies by sinking wells to a considerable depth in +situations where it appeared likely that the drainage from the +inland plateau would be specially abundant. But these have met with +little success; the yield has been found to be very moderate in +quantity, and of poor quality owing to dissolved salts. The +question has often been raised as to whether very deep borings, +carried down right through the Tertiary strata and into the Nubian +sandstone, might result in the procuring of an artesian supply of +the same excellent water as occurs in the oases. Hitherto it has +not been possible to give a definite answer to this question, and +geologists have been reluctant to recommend deep borings, which +would entail great expense, without feeling some assurance that +they would be successful. The depth to the Nubian sandstone is +unknown, but is certainly great; and if borings were carried down +into the sandstone, it was not known whether the water would rise +to anything like the ground-level. From our new map, however, we +obtain a very decisive verdict on the matter. The Nubian sandstone, +even if reached, would not be found to be charged with artesian +water under anything like the pressure that it is in the oases; +leakage into the Qattara and other depressions will have depleted +the beds of much of the water coming from the south-west, and will +have lowered the static head to such an extent, that the water left +in the sandstone will have too little pressure to rise far into the +bores. Any idea of sinking deep artesian wells along the coast to +tap the Nubian sandstone can consequently be definitely abandoned. +We are driven to the conclusion that in any attempt to improve the +local water-supplies of the<span class="pagenum" id= +"Page_118">[118]</span> littoral settlements, we can count only on +local rainfall for our primary source, and we must do our best to +collect the run-off before it has had an opportunity to absorb much +salt. The Romans evidently understood this when they excavated the +large rock-cisterns on the plateau, of which there are hundreds. We +cannot do better than imitate their example, and arrange for the +collection and storage of a sufficient volume of rainwater as it +runs from the rocky surface of the plateau. We may do this by +restoring to use the old reservoirs; or we might possibly achieve +our end by damming some of the rocky gullies which bring down the +run-off from the plateau to the plain. Now that the artesian idea +is shown to be out of the question, there is justification for a +thorough investigation as to the best method of collecting and +conserving the local rainfall.</p> + +<h2><a id="s07"></a>7. <em>Are the Artesian Water Supplies of the +Oases diminishing?</em></h2> + +<p>The native cultivators in certain parts of Kharga and Dakhla +have for some years past found that their wells no longer discharge +at so high a level as formerly, and in consequence some of their +land has gone out of cultivation. From this fact, and from the +evidence of the former greater prosperity of the oases which is +afforded by the various ruins of temples, forts, and villages, by +the large areas of formerly cultivated lands, and by numerous +sanded-up wells, it has sometimes been inferred that the total +yield of the oasis-wells is now but a fraction of what it formerly +was. But, as Mr. Beadnell has pointed out,<a id= +"FNanchor_24"></a><a href="#Footnote_24" class="fnanchor">[24]</a> +the remains of the past which exist in the oases belong to +successive generations, so that we cannot fairly draw such a +conclusion from them; and the reduction or cessation of the +discharge of certain wells does not necessarily imply any +falling-off in the total water-output of the oases. Mr. Beadnell’s +experiments on flowing wells in Kharga have clearly shown how the +opening of a new well at a slightly lower level will affect the +discharge of an old well, even one at a distance of a kilometre or +more, by lowering the static head in its vicinity.<a id= +"FNanchor_25"></a><a href="#Footnote_25" class="fnanchor">[25]</a> +And since a large number of wells have been bored in recent years +both in Kharga and Dakhla, it is most likely that the discharge +from these wells has caused a falling-off in the yield of older +ones situated at slightly higher levels. In this connection it will +be well to note that it is not the mere <em>existence</em> of a new +well that affects the static head, but the <em>discharge</em> from +it. If the new well is securely closed so as to discharge nothing, +it has then no effect on the static head and therefore none on the +neighbouring wells. But for this to hold, it is important that the +well which is closed should be closed throughout its entire depth; +it is not sufficient merely to close its mouth so that it does not +discharge any water on to the ground, for there may still be rapid +leakage somewhere in the bore (unless effectively cased) into +porous unsaturated underground<span class="pagenum" id= +"Page_119">[119]</span> strata. Owing to the rapid rate at which +iron pipes are corroded in the wells of the oases, leakage of this +kind is more likely to happen with an abandoned modern well cased +with iron piping and plugged near the top, than with old wells +which were filled up with clay and sand. These factors, the mutual +interference of wells and the importance of preventing underground +leakage, especially from abandoned wells, being now thoroughly +understood, steps are being taken towards ensuring that future +sites for new wells shall be judiciously selected, and that leakage +and waste from abandoned wells shall be as far as possible +arrested.</p> + +<p>The method of carrying out measurements of well-discharges in +the oases is so inaccurate, and the records of the past output so +defective, that it is not possible to gather from them whether the +total yield of artesian water is at present diminishing or not. Mr. +Beadnell considers it likely, however, that the general average +water-pressure in the oases has been very much reduced within the +historical period, owing to the long-continued exploitation of the +artesian supplies.<a id="FNanchor_26"></a><a href="#Footnote_26" +class="fnanchor">[26]</a> The general study of the Libyan Desert +which I have made in the last few years suggests that a gradual +reduction in the static water-pressure in the oases may possibly +have been brought about by other agencies than the exploitation of +the water in the oases themselves.</p> + +<p>The first and most important of these other agencies is the +withdrawal of artesian water by the Nile in the neighbourhood of +Dakka. As mentioned on <a href="#Page_113">p. 113,</a> it is +practically certain that sandstone beds carrying artesian water are +cut through by the Nile along a distance of several kilometres in +that locality, and the influx of artesian water into the Nile may +far transcend in quantity that removed by the wells and springs of +the oases. The Nile has probably deepened its channel in this +region by a few metres within historical times, and thus cut +through a greater section of the water-bearing beds. An increase in +the sectional area of the beds cut through would naturally mean an +increase in the quantity of artesian water passing into the Nile, +and hence a lowering of the static water-surface extending perhaps +to the oases.</p> + +<p>The second possible other cause operating to diminish the static +head of the artesian water of the oases is the progressive +desiccation of a lake which may once have occupied a part of the +Qattara depression. As mentioned on <a href="#Page_110">p. 110,</a> +the floor of this great depression, large areas of which are 80 +metres and more below sea-level, is partly covered by a salt-marsh, +which is so soft and watery that it can only be crossed at a few +places. The hundreds of great water-cisterns cut in the limestones +of the plateau to the north of the depression—cisterns most of +which are now dry—as well as other ruins along the coast indicative +of a considerable former population, seem to show that the rainfall +in the littoral region has within the historical period been +greater than it is at the present day. When the rainfall in the +coastal region was greater, there must have been<span class= +"pagenum" id="Page_120">[120]</span> more drainage into the Qattara +depression, and what is now salt-marsh was thus possibly once a +lake of some depth. Assuming, as I think is likely, that an +underground water-connection exists between the marsh occupying the +bottom of the depression and the artesian water of the oases, it is +obvious that any progressive lowering of the lake-level consequent +on the change of climate must have lowered the static water-surface +in the country extending southwards towards the oases. In the oases +themselves the lowering of the static surface would of course be +much less than at the lake; but it is quite conceivable that even +in the oases the lowering may have amounted to the few metres which +would cause some of the older and higher-lying wells to cease to +flow.</p> + +<p>As both the deepening of the Nile channel in Lower Nubia and the +desiccation of the Qattara depression are probably still slowly +progressive, it is possible that these causes may to some extent +account for any slow lowering of the static water-surface in the +oases which may be still going on.</p> + +<h2><a id="s08"></a>8. <em>“Lost” Oases—“Zerzura.”</em></h2> + +<p>Of all the questions asked by intending travellers in the Libyan +Desert, none is more frequent than that as to the most likely +whereabouts of undiscovered oases, and especially as to the +possibility of finding the mysterious “Zerzura, or Oasis of the +Blacks.” Hitherto the only aid which I have been able to render to +such inquirers has been to acquaint them with the various +statements which have been made by Arabs at different times as to +the situation of Zerzura, with the routes which have been followed +by others (including myself) who have sought in vain for it, and +with the indications of old tracks which have been encountered by +these previous travellers. So contradictory have been the various +Arab statements, and so numerous the vain attempts to find the +place, that I have at times felt almost convinced that “Zerzura” is +a myth. But Owenat and Merga were little more than traditions until +a year or two ago, and I think there is a sufficient possibility of +the existence of undiscovered springs or oases to encourage a +further look-out being kept for them, more especially as a +consideration of the general surface-contours and static +water-contours which are now available may furnish a new aid in the +matter by narrowing down the field of search.</p> + +<p>As regards Arab traditions concerning Zerzura, the earliest +account of them which I have been able to trace is that of Sir +Gardner Wilkinson in his ‘Topography of Thebes and General View of +Egypt,’ published in 1835, p. 359. Wilkinson’s book is now rather +scarce, and his statement concerning Zerzura is so short that I +quote it in full:</p> + +<div class="quote"> +<p>“About five or six days west of the road from el Hez to Farafra +is another Oasis, called Wadee Zerzoora, about the size of the +Oasis Parva, abounding in palms, with springs, and some ruins of +uncertain date. It was discovered about nine years ago +(<em>i.e.</em> about 1826) by an Arab in search of a stray camel, +and from the footsteps of men and sheep he there met +with,<span class="pagenum" id="Page_121">[121]</span> they consider +it inhabited. Gerbabo, another <em>Wah</em>, lies six days beyond +this to the west, and twelve days from Augela; and Tazerbo, which +is still farther to the west, forms part of the same Oasis; and +they suppose that Wadee Zerzoora also communicates with it. The +inhabitants are blacks, and many of them have been carried off at +different times by the Moghrebins for slaves; though the “Vallies +of the Blacks,” a series of similar Oases, lie still farther to the +west.”</p> +</div> + +<p class="space-above15">In footnotes he adds:</p> + +<div class="quote"> +<p>“It is supposed that the blacks, who invaded Farafreh some years +ago, and kidnapped a great number of the inhabitants, were from +this Oasis.</p> + +<p>“By another account Zerzoora is only two or three days due west +from Dakhleh, beyond which is another <em>wadee</em>; then a second +abounding in cattle; then Gebabo and Tazerbo; and beyond these is +Wadee Rebeeana; Gebabo is inhabited by two tribes of blacks, the +Simertayn and Ergezayn.”</p> +</div> + +<p>Particular interest attaches to Wilkinson’s account of the +tradition, not only because of its being the earliest, and +therefore less likely to be coloured by imagination than later +versions, but also because of the remarkable fact that although +some of the other places named in the above extract were unknown to +European geographers at the time, they have all since been +discovered; “Gebabo” and “Tazerbo” by Rohlfs, and “Rebeeana” by +Mrs. Forbes and Hassanein Bey.</p> + +<p>The weak point in the account is the loose Arab way of stating +directions. Gebabo (Kufra) is not <em>west</em> of the +Baharia-Farafra road, but south-west. If we amend the bearing in +the first account accordingly, and take Zerzura at about midway +between the Baharia-Farafra road and Kufra, it must lie near the +intersection of the parallel of 26° with the meridian of 26°, or +some 200 kilometres east of the Mehemsa Hattia, and some 150 +kilometres north-west of Rohlfs’ “Regenfeld” camp. In the second +account given by Wilkinson, the words “due west” suggest that the +bearing is more certain. Two or three days (say 120 kilometres) due +west of Dakhla would put Zerzura in about latitude 25½°, longitude +27½°, or about 30 kilometres north of Rohlfs’ “Regenfeld.” There is +thus a difference of more than 100 kilometres between the two +positions indicated by the accounts given to Wilkinson.</p> + +<p>Rohlfs evidently knew of the traditions regarding Zerzura before +making his attempt to reach Kufra from Dakhla in 1874; and since +such an intermediate oasis, if it really existed, would be an +immense aid to him in attaining his objective, he made careful +inquiries concerning it before leaving Dakhla. But he found that +though every one in Dakhla knew the names of Zerzura and Kufra, no +one could tell him where Zerzura was, nor how far it lay from +Dakhla.<a id="FNanchor_27"></a><a href="#Footnote_27" class= +"fnanchor">[27]</a> Evidently Rohlfs placed little faith in its +existence, for during his journey he gave the name “Zerzura” to a +locality, about 120 kilometres west-south-west of<span class= +"pagenum" id="Page_122">[122]</span> Dakhla, where he found nothing +but very sparsely scattered vegetation.<a id= +"FNanchor_28"></a><a href="#Footnote_28" class="fnanchor">[28]</a> +Ascherson, who was with Rohlfs in Dakhla, was however informed by +Hassan Effendi, one of the principal inhabitants of Mut, that about +a hundred years before (<em>i.e.</em> about 1770) there had been +frequent raids on Dakhla by Arabs from the south-west; and that in +order to stop these raids the Mameluke Government of the time +installed a military colony, called the Surbaghi, in the village of +Qalamun. These Surbaghi went out and destroyed all the wells for +seven or eight days’ distance along the road by which the raiders +had come. This road, which up to that time had served as a trade +route from Darfur, before the road through Kharga was opened, was +in consequence forsaken. The road was said still to exist, and to +lead into the desert from Mut. At a day-and-a-half’s journey from +Mut there were said to be two “pillars,” half an hour’s distance +apart, which Hassan Effendi’s guard likened to minarets. In the +neighbourhood there were said to be large stone-quarries, and about +thirty years previously an iron instrument had been found; the +instrument was still in Hassan Effendi’s possession, and some +wonderful stories had grown up as to the manner of its use.<a id= +"FNanchor_29"></a><a href="#Footnote_29" class= +"fnanchor">[29]</a></p> + +<p>Ascherson himself believed this information of Hassan Effendi’s +to be substantially correct, but he thought the “pillars” might be +merely pinnacle-shaped natural rocks. I am likewise inclined to +believe it trustworthy, but I think the “wells” may have been +merely water-dumps—that is, collections of jars of water. My reason +for this view is twofold. In the first place, the ground-levels in +that part of the desert are so far above the static water-level, +that if wells were bored they would have to be very deep, and the +water would not rise anywhere near the surface (there can, of +course, be here no question of local rainfall as a source for the +water in the “wells”); and in the second place, it seems very +probable that the accumulation of large broken earthenware jars +which I discovered in 1916 at the place I named “Pottery Hill” +(latitude 24° 26′ 27″, longitude 27° 38′ 54″) is one of the dumps +in question.<a id="FNanchor_30"></a><a href="#Footnote_30" class= +"fnanchor">[30]</a></p> + +<p>The importance of the above interpretation of Hassan Effendi’s +story,<span class="pagenum" id="Page_123">[123]</span> if accepted, +as I think it must be, lies in the proof which it furnishes that +there cannot possibly be an undiscovered oasis anywhere near a +point seven or eight days from Dakhla in the direction of Kufra. A +consideration of the static water-levels and the contours of the +ground would lead us to this conclusion if the views I have +advanced on the underground-water question are correct; but the +fact that the raiders would never have made such a large water-dump +if water could have been readily got from a well in the vicinity +makes the conclusion almost certain independently of my hypothesis, +and thus incidentally tends to support the latter. Is it possible +that “Zerzura,” which I am told signifies in Arabic a starling (but +is commonly applied to any small bird), is here a corruption of +some other name derived from “zeer,” a water-jar, and that instead +of “the <em>oasis</em> of the blacks,” Zerzura was really “the +<em>water-depôt</em> of the blacks”?</p> + +<p>Schweinfurth has recorded<a id="FNanchor_31"></a><a href= +"#Footnote_31" class="fnanchor">[31]</a> a story which was told him +in Kharga Oasis, that in 1872 some Arabs of a Darfur caravan, who +had missed the road, found a small oasis about 1½ days’ journey to +the west of Beris. The oasis was said to contain pools full of wild +geese, date-palms, and a temple. People who went out of Beris to +find the place returned unsuccessful. I am, however, rather +inclined to think that the story has some basis of fact, because in +1898 I myself found springs and traces of ancient conduits in the +dunes north-west of Beris, and there may be other water-sources +beyond the point which I reached.<a id="FNanchor_32"></a><a href= +"#Footnote_32" class="fnanchor">[32]</a></p> + +<p>A writer in the ninth edition of Murray’s ‘Guide to Egypt,’ +published in 1896, gives the following different statements of +Arabs as to the position of Zerzura:</p> + +<p>(1) Some days south of the Dakhla Oasis.</p> + +<p>(2) Five days west of Farafra Oasis.</p> + +<p>(3) Three days west of Dakhla Oasis.</p> + +<p>(4) Two or three days west of Selima Oasis.</p> + +<p>The first of these statements would correspond sufficiently well +with Bir Terfawi, which is about 280 kilometres due south of Dakhla +Oasis; the second would place Zerzura about in latitude 27°, +longitude 26°; the third corresponds with the second account given +to Wilkinson; while the fourth would place it far to the +south-west, in latitude 21½°, longitude 28°, or rather less than +halfway between Bir Terfawi and Merga.</p> + +<p>Mr. Harding King, who in his journeys in the Libyan Desert in +1909 and 1911 devoted much attention to the collecting of native +information regarding its geography, thinks that “Zerzura” may +possibly be only a generic name applied to any mythical or +undiscovered oasis.<a id="FNanchor_33"></a><a href="#Footnote_33" +class="fnanchor">[33]</a> He heard the name applied to the +following localities:</p> + +<p class="hang2"><span class="pagenum" id= +"Page_124">[124]</span>(1) Rohlfs’ “Sersura.”</p> + +<p class="hang2">(2) The “Egyptian Oasis,” said to have been seen +by an Arab from the top of a high black hill lying in the dune-belt +ten long days by ordinary caravan from Kharga. Another Arab is said +to have seen what is possibly the same place eight days somewhere +to the south of Dakhla. Both these accounts agree that the place is +a large oasis lying at the foot of a scarp and containing olive +trees.</p> + +<p class="hang2">(3) A stone temple eighteen hours’ journey west of +Gedida in Dakhla Oasis.</p> + +<p>The information given to Mr. Harding King as to the position of +the “Egyptian Oasis” would place it about in latitude 23°, +longitude 28½°, or only some 50 kilometres north-west of Bir +Terfawi; in fact, considering the vagueness of the information, it +might correspond fairly well with Terfawi itself, except that there +are no olive trees at Terfawi, nor is that place overlooked by any +escarpment or hill. The “high black hill in the dune-belt” may just +possibly be one of those I mapped near the farthest point I reached +with Moore in 1916, in about latitude 24°, longitude 26°, though +this would imply a direction south-west of Dakhla, not south. It is +not likely to be Gebel Kamil, as that mountain lies much nearer to +Merga than to Dakhla.</p> + +<p>The “stone temple,” according to the information given to Mr. +Harding King, would be about 80 kilometres west of Dakhla Oasis, in +about latitude 25½°, longitude 28°, or not very far from the second +of the positions indicated by Wilkinson for Zerzura. But I think it +is likely that the statement really refers to the “Deir el Hagar,” +a well-known temple ruin much nearer to Dakhla.</p> + +<p>So much for the various statements as to whereabouts Zerzura +<em>may be</em>. Let us now inquire where it is <em>not</em>. On +the map I have indicated the principal routes followed by explorers +of the southern and western parts of the Libyan Desert during the +last fifty years. We may be tolerably certain that Zerzura is not +on, or very close to, any of these routes; for although a +depression within a kilometre or so of one’s track may easily be +passed without notice, the existence of a large oasis, such as most +of the traditions make Zerzura out to be, would almost certainly be +betrayed to an explorer by animal-tracks leading to it from +considerable distances, except possibly in places where the ground +was very sandy.</p> + +<div class="figcenter iw1"> +<figure id="i16"><img src='images/i16.jpg' alt=''> +<p class="cp1"><em>Pottery Hill from the south: at foot, petrol and +water supplies of Prince Kemal el Din’s Expedition of 1923</em> +</p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i17"><img src='images/i17.jpg' alt=''> +<p class="cp1"><em>Jars at northern foot of Pottery Hill found by +Prince Kemal el Din in 1923</em> +</p> +</figure> +</div> + +<div class="figcenter iw2"> +<figure id="i18"><img src='images/i18.jpg' alt=''> +<p class="cp1"><em>Jars, worn away by sand-laden winds, found by +Dr. Ball in 1917 at southern foot of Pottery Hill</em> +</p> +</figure> +</div> + +<p>There is another method now available to us by which we may +narrow down the search for Zerzura or other “lost” oases; and that +is, by a consideration of the general contours of the country and +those of the static water-surface. Every oasis in the Libyan Desert +must owe its existence to one or other of two conditions: either it +must depend on springs fed by local rainfall, in which case, like +the oases of Owenat and Arkenu, it probably lies near to mountains +of considerable height; or else it must depend on underground +supplies, and must therefore lie in<span class="pagenum" id= +"Page_125">[125]</span> a depression wherein the ground-level and +static water-level are practically coincident, as in the cases of +Kharga, Dakhla, Farafra, Baharia, and Siwa. It is highly doubtful +whether any mountain masses at all approaching the altitude of +Arkenu and Owenat can remain undiscovered in any of the various +areas in which Zerzura has been traditionally placed. Zerzura is +immensely more likely to be in a depression, and indeed Wilkinson’s +name <em>Wadi</em> Zerzura almost conclusively points to that view. +The depression is more likely to be shallow than very deep, for it +presumably lies in the sandstone country of the south-west, and all +the known depressions of great depth are confined to the limestone +country of the north-east. It is quite easy to trace out on our new +map the areas wherein the static water-surface would be reached by +a depression of say 50 or 100 metres below the general ground-level +as indicated by the contours. We must, however, remember that our +ground-contours are liable to be considerably in error in areas +where observations have been few—that is, in precisely those areas +where the depression, if it exists, is most likely to be found. So +we must allow a good margin for our depth, and I have chosen 100 +metres on this account. On the <a href="#map2">map</a> I have drawn +the “locus” of points in the southern part of the Libyan Desert +where the static water-surface is 100 metres lower than the general +ground-surface<a id="FNanchor_34"></a><a href="#Footnote_34" class= +"fnanchor">[34]</a>; and I have edged with red the only areas in +the west and south in which the two surfaces are within 100 metres +of each other—that is to say, the areas within which comparatively +shallow depressions with underground springs <em>must</em> lie, if +our contours of the two surfaces are drawn with even approximate +correctness. It will be seen from the map that this restricts the +search very considerably. In fact, if Zerzura is within the +frontiers of Egypt, it lies in all probability either to the west +of longitude 26° 20′ and north of latitude 26°, or to the east of +longitude 27° and south of latitude 23° 30′. We may dismiss from +our field of search all the broad tract of rising ground which +extends from near the Dakhla escarpment south-westwards towards +Owenat; for unless Zerzura is in a depression of great depth, it +cannot possibly lie within this tract. This consideration shows +that most of the previous rough estimations of the possible +position of Zerzura must have been erroneous; and indeed it is +remarkable how few of the various explorers’ tracks traverse the +only two areas within which Zerzura, if it exists, almost certainly +lies. The northern area has only been crossed by the Rohlfs +expedition of 1874, and that near its eastern edge; while the +western part of the southern area has only been crossed by Prince +Kemal el Din’s expedition of 1925. Of all the Arab traditions, only +those which would place Zerzura far to the west of Farafra, or far +to the south-south-west of Dakhla, can now have any high degree of +credibility. It can hardly, I think, be doubted that +the<span class="pagenum" id="Page_126">[126]</span> various +traditions refer to more than one place; and in view of the almost +totally unexplored state of the only two areas in which our new +contour-maps indicate the possibility of unknown oases existing, it +is quite conceivable that at least one oasis may lie within each of +them. In the northern area, Siwa would probably make the best +starting-point from which to conduct a search, as it is easily +reached by motor-car from Alexandria or Cairo, and exploratory +journeys southwards from Siwa would mostly lie along the direction +of the dune axes. In the southern area, Terfawi or Sheb would form +the best base for exploration; at each of these places there is a +good water-supply. I am inclined to think that the southern area is +more likely to yield results than the northern one. Water was found +to exist at a point some 15 kilometres west of Terfawi, and though +no other source was observed on the way to Owenat, it was +impossible to see very far on either side of the track, so that +such a source might have been passed within a few miles without +notice. Terfawi itself is very difficult to find, being +inconspicuous even when one is fairly close to it; and as it is in +a sandy area, tracks leading to it are soon obliterated. Another +factor which favours this southern area is that, the country being +all Nubian sandstone, the depth from the surface to the actual +water-bearing beds (as distinguished from the depth to the static +water-surface) is certain to be much less than in the northern +area, where Cretaceous strata may overlie the sandstone; hence +there is more likelihood of the existence of natural springs in the +south than in the north.</p> + +<h2><a id="s09"></a>9. <em>Can Travel in the Great Tracts of the +Libyan Desert which are now Waterless be facilitated by the Sinking +of New Wells?</em></h2> + +<p>It has sometimes been asked whether tracts which it is now +difficult or impossible to cross by camel, owing to the +non-existence of wells or natural springs within them, might +possibly be opened up to transport by the sinking of new wells +along a proposed route, as has in fact been done by the Senussi in +the case of the well at Sarra, between Wanianga and Kufra. Hitherto +there have been no data from which to form an opinion on this +question; but a study of the new map will enable at least a +qualified answer to be given.</p> + +<p>To be a practicable proposition, a new well must fulfil two +conditions: the first, that the boring must not be required to +descend to a very great depth; and the second, that the water when +struck must rise in the bore to within a reasonable distance, say +20 to 30 metres, of the ground-level at the place. The first of +these conditions will be satisfied if the geological horizon of the +water-bearing bed is comparatively near the surface; the second, if +the level of the static water-surface in the locality is within 20 +or 30 metres of the ground-level.</p> + +<p>As regards the first of these conditions, we know that the +water-bearing beds underlying the Libyan Desert are situated within +the geological<span class="pagenum" id="Page_127">[127]</span> +formation called the Nubian sandstone. We may therefore eliminate +from our consideration all tracts in which this formation is +overlain by any great thickness of younger rocks, for all these +rocks will have to be passed through in order to tap the +water-bearing strata.</p> + +<p>Concerning the second condition, our map at once informs us that +the areas in which the static water-surface is within 20 or 30 +metres’ depth below the ground-level are decidedly limited. Even if +we suppose that there may be unknown depressions extending to a +depth of 70 metres below the general level of the country indicated +by the contour-lines, we see that the localities in which the +second condition would be fulfilled are confined to the tracts +edged with red on the map. Outside these tracts, not only have we +no chance of discovering oasis-depressions, but we also have no +prospect of being able to bore wells in which water would rise to +within a reasonable distance of the ground-level. Thus the broad +tract of rising ground which extends south-westwards from Dakhla to +Owenat must always remain a waterless waste.</p> + +<p>In the Egyptian portion of the Libyan Desert there are, as will +be seen from the map, only two areas in the west and south in which +new wells might successfully be bored: one extending for some 300 +kilometres or so to the south of Siwa Oasis in the neighbourhood of +the western frontier, the other extending for some 400 kilometres +westward from the Nile in the neighbourhood of the southern +boundary. Fortunately, however, these areas are so situated that +wells sunk within them might be of considerable use in opening up +the outermost parts of Egypt to exploration. A well near the +western frontier about on the parallel of 26°, for instance, might +make it just possible for cars or camels to reach Owenat directly +from Siwa, since it would divide the present waterless stretch of +830 kilometres into two stretches of about half that length; while +one or two wells near the southern frontier between the meridians +of 27° and 28° would render Owenat fairly accessible to camels +coming from the Nile <em>viâ</em> Terfawi or Sheb, and might be of +great use to explorers or geologists desirous of making a detailed +investigation of the Owenat and Arkenu region. From the little I +saw of Gebel Owenat during my visit to it in 1925, its geology must +be of extreme interest. The south-western part of the mountain +appears to be entirely composed of granite and other crystalline +rocks, while the eastern part presents huge cliffs of sandstone, +with crystalline rocks showing only at the foot; there is evidently +a great fault traversing the mountain mass, with a downthrow to the +east; and the thickness of Nubian sandstone exposed on the eastern +precipices is greater than that at any other place I have +seen.<a id="FNanchor_35"></a><a href="#Footnote_35" class= +"fnanchor">[35]</a> Gebel Kissu probably resembles the +south-western part of Owenat in being<span class="pagenum" id= +"Page_128">[128]</span> entirely composed of crystalline +rocks.<a id="FNanchor_36"></a><a href="#Footnote_36" class= +"fnanchor">[36]</a> East of Gebel Owenat there are many igneous +hills, some of which exhibit bands of a dark brown colour. These +bands, though probably mostly igneous dykes, may possibly in some +cases be the gozzany outcrops of veins containing metallic +minerals; I had no opportunity of examining them at close quarters, +but I saw enough to make me long for facilities to undertake such +an examination.</p> + +<p>It may be remarked that a well in the northern area would +probably have to be very deep, owing to the comparatively high +geological horizon of the surface rocks there; but in the southern +area, where the Nubian sandstone forms the surface rock, no great +depth of boring would be likely to be required in order to tap the +water-bearing beds.</p> + +<p>Apart from the question of new wells in the more remote parts of +the Libyan Desert, a study of the map gives us some hints which may +be of value should it ever be desired to sink wells in places +nearer to the oases and to the well-known tracks. There appears, +for instance, to be no reason why wells should not be successfully +bored at intervals along the Darb el Arbain between the south end +of Kharga and Lagia, or on the south side of the Qattara and other +depressions of the northern part of the desert. In the southern +area, the best sites to select for wells will be depressions +wherein the ground-level approximates most closely to the static +water-level; and readings of an aneroid barometer, compared with +corresponding readings at a place of known altitude, such as Sheb +or Terfawi, would enable the most favourable sites to be +determined. Observations of the geological structure will also be +of importance; for anticlinal folds, by bringing the water-bearing +strata nearer to the surface, would diminish the depth to which +borings would have to be carried to tap the beds; while faulting +might likewise introduce favourable conditions by producing cracks +and fissures along which the water could rise. It may be remarked +that tamarisk-bushes are generally a sign that water exists at no +great depth. In regard to wells in or near the northern +depressions, it is obvious that sites on the south side of the +lakes and salt-marshes should be selected; for not only is the +artesian static level higher in the south, but the water is less +likely to be contaminated by salts derived from the lake and +marshes.</p> + +<h2><span class="pagenum" id="Page_209">[No. 3<br> +209]</span><a id="s10"></a>10. <em>The “Tortoise Marshes” of +Ptolemy.</em></h2> + +<p>The passage in Ptolemy’s ‘Geographia’ (lib. IV. cap. 6, sect. 4) +in which the position of the “Tortoise Marshes” is given may be +translated as follows<a id="FNanchor_37"></a><a href="#Footnote_37" +class="fnanchor">[37]</a>:</p> + +<p class="pad4">There are two great rivers running into the +Mediterranean; one of them is the Gir, joining Mount Usargala with +the Garamantic narrows, from which, changing its course, the river +is located in long. 42°, lat. 16°, and makes the Tortoise Marshes +(Chelonitides Paludes), whose position is long. 49°, lat. 20°.</p> + +<p>The information on which Ptolemy based this statement, at least +as regards the river <em>Gir</em>, must have been very fragmentary, +if not, indeed, grossly erroneous; for there is no river flowing to +the Mediterranean anywhere near the positions he gives. But there +can be little doubt that his names <em>Gir</em> and +<em>Chelonitides Paludes</em> refer to real places, and there has +been much speculation among geographers as to their +identification.</p> + +<p>Thus, for instance, Knoetel<a id="FNanchor_38"></a><a href= +"#Footnote_38" class="fnanchor">[38]</a> suggested that the +<em>Gir</em> may have been the Wadi Djedi, to the south of Biskra, +and the Tortoise Marshes the modern Lake Melghir (lat. 34°, long. +6°)<a id="FNanchor_39"></a><a href="#Footnote_39" class= +"fnanchor">[39]</a> Dr. William Smith<a id= +"FNanchor_40"></a><a href="#Footnote_40" class="fnanchor">[40]</a> +thought that the <em>Gir</em> was really a branch of the Niger, and +the marshes the modern Lake Fittri (lat. 13°, long. 18°). On the +map of Africa on the 2-million scale published by the Geographical +Service of the French Army in 1899 the Tortoise Marshes are +depicted as lying in about latitude 19° 20′,<span class="pagenum" +id="Page_210">[210]</span> longitude 27°, with a note stating that +this delineation is taken from an earlier map of the Nile Basin by +Miani, who regarded the marshes as being connected with the “dry +river” which was then supposed to run northwards through Dakhla +Oasis. Colonel Tilho has lately suggested<a id= +"FNanchor_41"></a><a href="#Footnote_41" class="fnanchor">[41]</a> +the lowlands to the north-east of Lake Chad (lat. 18°, long. 17°) +as a possible site for the marshes; while still more recently Mr. +Harding King<a id="FNanchor_42"></a><a href="#Footnote_42" class= +"fnanchor">[42]</a> has thought that they might perhaps be +identified with the salt lake of Merga (lat. 19° 3′, long. 26° +19′).</p> + +<p>Of the various localities which have been suggested as possible +sites for the Tortoise Marshes, the only one which I have visited +is Merga. I found the salt lake at that place to be very small, +covering only some 10 acres; it lies at an altitude of 509 metres +above sea-level, and though it is situated in a rather wide shallow +depression, I saw no traces of any extensive salt-marshes around +the lake, while the configuration of the surrounding country +appeared to me to be such that the depression cannot possibly have +formed part of a continuous drainage-channel.</p> + +<p>I do not know whether it has hitherto been suggested that Kufra +Oasis may be the site of the Tortoise Marshes; but on correcting +Ptolemy’s figures for the errors in his adopted position for +Alexandria and in the length which he assumed for a degree of +latitude, I find Kufra is in very much closer agreement with them +than any of the places named above. In Ptolemy’s day, even the +latitudes of but few places had been astronomically observed +(Alexandria, where he himself resided, was supposed by Ptolemy to +be in latitude 31°, instead of its true 32° 12′), and as the only +method at that time known for astronomically determining +differences of longitude was by the observation of eclipses, the +number of observed longitudes was smaller still. The process by +which Ptolemy deduced his position for the Tortoise Marshes and +other places in the interior of Libya was most probably that of +first estimating their distances south and west of Alexandria from +travellers’ itineraries, then converting these distances into +degrees of latitude and longitude, and finally subtracting the +differences thus found from the latitude and longitude of +Alexandria. But Ptolemy made the great mistake of assuming the +length of a degree of latitude (or of equatorial longitude) to be +500 stades, instead of the 700 stades which it really is. Thus all +his dead-reckonings resulted in differences of latitude and +longitude which were too great in the proportion of seven to five. +If we correct Ptolemy’s position for Alexandria, and his +dead-reckoning for the erroneous assumption which he made regarding +the size of the Earth, as follows:</p> + +<table class="tless" id="t210"> +<tr> +<th> +</th> +<th><em>Latitude.</em> +</th> +<th class="width2"> +</th> +<th><em>Longitude.</em> +</th> +</tr> + +<tr> +<td class="tdl-top hang3">Ptolemy’s position for Alexandria</td> +<td class="tdl-bot">31°</td> +<td> +</td> +<td class="tdl-bot">60° 30′</td> +</tr> + +<tr> +<td class="tdl-top hang3">Ptolemy’s position for the Tortoise +Marshes</td> +<td class="tdl-bot bb">20°</td> +<td> +</td> +<td class="tdl-bot bb">49°</td> +</tr> + +<tr> +<td class="tdl-top hang3">Ptolemy’s difference of lat. and +long.</td> +<td class="tdl-bot">11°</td> +<td> +</td> +<td class="tdl-bot">11° 30′</td> +</tr> + +<tr> +<td class="tdl-top hang3"><span class="pagenum" id= +"Page_211">[211]</span>These differences reduced in the proportion +of 5 to 7 become, in true degrees and minutes</td> +<td class="tdl-bot"><span class="word-spaced03em"> </span>7° +52′</td> +<td> +</td> +<td class="tdl-bot"><span class="word-spaced03em"> </span>8° +12′</td> +</tr> + +<tr> +<td class="tdl-top hang3">The true position of Alexandria is</td> +<td class="tdl-bot bb">32° 12′</td> +<td> +</td> +<td class="tdl-bot bb">29° 53′</td> +</tr> + +<tr> +<td class="tdl-top hang3">Whence the corrected position for the +marshes in our modern system becomes</td> +<td class="tdl-bot">24° 20′</td> +<td> +</td> +<td class="tdl-bot">21° 41′</td> +</tr> +</table> + +<p class="nind">we get lat. 24° 20′ and long. 21° 41′ for the +Tortoise Marshes. Comparing this position with that of Kufra, we +find that the latitude agrees very closely with the 24° 14′ which +Hassanein observed at Taj, the principal village of that oasis; +while the longitude, though more than a degree and a half west of +that of the principal village, is almost exactly correct for +Taiserbo, the north-western oasis of the Kufra group.</p> + +<p>Besides this remarkably close agreement as regards position, +Kufra presents several natural features which would tend to support +the view that it may be the locality which Ptolemy meant by the +“Tortoise Marshes.” Not only is Kufra an extensive tract of +relatively low-lying ground with numerous lakes and salt-marshes of +very considerable size, but it has distinctly the form of a valley. +Hassanein Bey repeatedly refers to it as a valley in his +description<a id="FNanchor_43"></a><a href="#Footnote_43" class= +"fnanchor">[43]</a>; Mrs. Forbes also speaks of the “Wadi of +Kufra,” and mentions that as a result of a ride westward from Taj +the “wadi” was found to have no definite ending to the west.<a id= +"FNanchor_44"></a><a href="#Footnote_44" class="fnanchor">[44]</a> +What more natural, therefore, than that some ancient traveller +should have imagined that Kufra was a series of marshes formed by a +river coming from the south-west? And is it not possible that +Ptolemy, in endeavouring to piece together the scraps of +information he could get, may have mistakenly inferred that this +river ultimately reached the Mediterranean, and also have confused +the account of it with those of other streams further south, which +may have been branches of the Niger?</p> + +<h2><a id="s11"></a>11. <em>The Sand-Dunes.</em></h2> + +<p>The sand-dunes of the Libyan Desert have been the subject of +careful studies by Mr. Beadnell and Mr. Harding King, and +practically all that was known concerning them up to the outbreak +of the Great War is contained in the excellent papers by them which +were read and discussed at meetings of the Royal Geographical +Society in 1910, 1916, and 1918.<a id="FNanchor_45"></a><a href= +"#Footnote_45" class="fnanchor">[45]</a></p> + +<p>With the commencement of the Senussi campaign in Egypt in 1915, +the sand-dunes sprang into new and unexpected importance, from the +fact that they formed one of the principal hindrances to the free +movement of troops, and more especially of military motor +transport, across the desert. Every line of dunes of any +considerable extent had now to<span class="pagenum" id= +"Page_212">[212]</span> be carefully mapped and examined for +possible car-passages through it; the result was to add greatly to +our knowledge of the distribution and extent of these remarkable +features of the Libyan Desert, especially in the northern parts, +where many long lines of dunes were found of which the existence +was previously unsuspected by geographers, though they are familiar +landmarks to the Bedouin of the region, and all except the smallest +bear Arabic names. After the cessation of hostilities, interest in +the distribution of dunes was maintained, because of the increasing +use of motor-cars in place of camels for transport across the +desert; and this circumstance has recently led to light being +thrown on the distribution of the dunes in those southern regions +which lay outside the field of operations during the war.</p> + +<p>It is rather curious to note that although the sand-dunes form +the greatest obstacle to motor-cars in the desert, yet it is +chiefly by means of motor-cars that the true extent and +distribution of the sand-dunes has been ascertained. Dunes are the +most difficult of all desert features to map properly by ordinary +reconnaissance methods with camel transport. Their smooth outlines +provide no points on which intersections can be made, and no survey +marks put on them will remain in place for more than a few hours, +or at most a few days; they occur mostly in nearly level country, +where it is impossible to find a station whence they can be +overlooked; the absence of shadows on them renders it impossible to +say whether one is looking at a single line of dunes, or at several +lines, miles apart, one behind the other in echelon. The only sure +way of mapping dunes is to traverse their sides along their entire +length, and this is impracticable with camels owing to the enormous +distances which would have to be covered without water. But with +motor-cars one can run alongside them at 40 kilometres an hour +instead of the camel’s 4, and their distribution can thus be +rapidly and easily ascertained.</p> + +<div class="figcenter iw1"> +<figure id="i19"><img src='images/i19.jpg' alt=''> +<p class="cp1"><em>Prince Kemal el Din’s expedition of 1925 leaving +Bir Terfawi for the waterless journey of 250 miles to Owenat</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i20"><img src='images/i20.jpg' alt=''> +<p class="cp1"><em>The well at Bir Terfawi in the palm clump</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i21"><img src='images/i21.jpg' alt=''> +<p class="cp1"><em>Jebel Owenat from the south: the triple peak +(5635 feet) in centre</em> +</p> +</figure> +</div> + +<div class="figcenter iw1"> +<figure id="i22"><img src='images/i22.jpg' alt=''> +<p class="cp1"><em>The lake at Merga located by Prince Kemal el +Din’s expedition of 1925</em> +</p> +</figure> +</div> + +<p>On the <a href="#map2">map</a> I have shown the distribution of +sand-dunes as far as it is known at the present day. A comparison +of this latest map with that given by Mr. Beadnell in his paper of +1910 will show how large is the number of dunes discovered and +mapped in more recent years; and it will be noticed how pronounced +is the constancy of the general direction of all the lines in the +Egyptian portion of the Libyan Desert. Though no new lines of dunes +comparable in extent with the great Abu Moharik belt have been +added to the map, some of the newly discovered lines are of very +considerable length, and they show an even more remarkable ratio of +length to breadth than the Abu Moharik belt; the Ramak dunes, for +instance, extend from near Moghara south-south-eastwards in a +straight line for more than 100 kilometres, with only a single +small break, and their width nowhere exceeds 1 kilometre. Moreover, +the linear arrangement in a direction from about 20° west of north +to about 20° east of south is even more pronounced in the newly +discovered northern dunes than it is in those previously known +farther south. In the “great<span class="pagenum" id= +"Page_213">[213]</span> sand sea” of Rohlfs, to the west of Dakhla +and Farafra, the same directional arrangement of the individual +lines of dunes is very noticeable, at least in the part near +“Regenfeld” where I have penetrated it; and I found the same +general direction to hold for most of the lines of dunes which I +crossed on the way from Terfawi to Owenat. During the war I +received a number of reports of dunes extending nearly east and +west, often in curved lines; but investigations on the spot showed +practically all these reports to be erroneous, the commonest +mistake having been that of sighting different lines of dunes from +different places under the impression that they were a single +one.</p> + +<p>The general south-south-easterly direction which is so marked a +feature of the lines of dunes in the Egyptian portion of the Libyan +Desert is not, however, preserved in the extreme south-west of the +country. The line of dunes which crosses the Egypt-Sudan frontier +in longitude 25° 40′ has a direction of about 30° <em>west</em> of +south, and the dunes which extend from near Gebel Arkenu to the +west of Gebel Owenat run about 38° west of south. From a point +about 80 kilometres to the south-west of Gebel Owenat, the +dune-lines make a still further distinct bend to the west, changing +their direction by some 20° to about 58° west of south, and this +latter direction is maintained by the dunes in the neighbourhood of +Sarra Well.<a id="FNanchor_46"></a><a href="#Footnote_46" class= +"fnanchor">[46]</a> According to the maps of Rohlfs and Mrs. +Forbes, the dunes in the sandy tract to the north-west of Kufra +follow approximately the same bearing as those near Sarra. The +suggestion has been made that this swinging round of the direction +of the dunes in the south-western part of the Libyan Desert may be +due to a deflection of the prevailing wind by the mountain-masses. +It is almost certainly caused by differences in the prevailing +winds—in fact, the dune-lines probably afford a very exact index to +the general wind-direction in the areas where they occur—but I am +inclined to think that the regional distribution of atmospheric +pressure, rather than local deflection by mountain masses, is the +cause of the differences of wind-direction. The dunes, especially +those near Sarra and Kufra, extend into localities which seem to me +to be too distant from the mountains for the influence of the +latter on the prevailing winds to afford a satisfactory +explanation.<a id="FNanchor_47"></a><a href="#Footnote_47" class= +"fnanchor">[47]</a></p> + +<p>In certain areas, especially in the south, as for instance on +the Arbain road from Kharga to Sheb, around Pottery Hill, and in +the region between Owenat and Erdi, there are sand-covered tracts +which can<span class="pagenum" id="Page_214">[214]</span> hardly be +mapped as dunes, because there are no very marked crests. These +tracts are easily crossed by camels, but give much trouble with +cars, and would probably be classed as dunes by car-drivers; but +they are really only vast undulating fields of drifted sand. On the +old Darb el Arbain slave road between Kharga and Sheb, one travels +for more than 100 miles over drifts of this kind. No footprint of +camel marks the track, footprints being obliterated in an hour or +two. But one is never in doubt about the way, for it is indicated +by the skeletons of countless camels which have perished on the +weary march.</p> + +<p>As regards the relation between dunes and the relief of the +ground, there is a gradual rise in the general level of the country +from north to south of about 1 in 1000, so that the southern ends +of most of the Egyptian lines of dunes lie at higher altitudes than +the northern ends; but I am fairly certain that this slight general +inclination has nothing to do with dune-formation. The straightest +and cleanest-cut lines of dunes are found in the flattest and most +open parts of the desert, over which the wind can sweep without +obstruction. When a line of dunes encounters in its southward +progression a sudden fall in the ground-level, as for instance at +the north end of Kharga Oasis and to the east of Pottery Hill, it +usually breaks up; sometimes, as in Kharga, to resume its course as +dunes in more open formation, and at other times, as near Pottery +Hill, to spread out into a rolling plain of drifted sand. It is not +uncommon for the south end of a line of dunes to split up, even on +level ground, and the same can be seen, though less often, at the +northern ends; but this is probably merely because the dunes are +lower near the ends of the lines, and the width of the individual +dunes is consequently less.</p> + +<p>The great lines of dunes are probably extending southwards at a +very slow rate, under the action of the prevailing wind. In this +connection it is interesting to note that Arabs always speak of the +south end of a line of dunes as its head, and of the north end as +its tail; just the opposite of what one would instinctively call +them from merely looking at the map, but correct if the dunes are +known to have a southward progression. Mr. Beadnell found the +average rate of progression of isolated small dunes in Kharga to be +15 metres per annum; but he remarks that large dunes move more +slowly than small ones, owing to the greater mass of material to be +transported. It is interesting to make a rough guess at the +antiquity of the dunes from the length of certain of the longer +lines and an estimated rate of progression. The Abu Moharik belt, +for instance, has a total length of about 350 kilometres; hence, if +its tail has remained stationary and its head has advanced +southwards at an average rate of 10 metres a year, some 35,000 +years must have been occupied in its formation.</p> + +<p>As regards the height of the dunes, the only one I have +carefully measured is that close west of Rohlfs’ camp at Regenfeld, +which I found to be exactly 30 metres. Some of the dunes in the Abu +Moharik and<span class="pagenum" id="Page_215">[215]</span> Ramak +belts are considerably higher; but I doubt if any of the Libyan +dunes rise much over 50 metres above ground-level, except in the +“great sand sea” which commences some 14 kilometres to the +north-west of Regenfeld, where Jordan estimated them to attain 100 +metres or more.<a id="FNanchor_48"></a><a href="#Footnote_48" +class="fnanchor">[48]</a> The top of a high dune to the south of +Melfa Oasis was found by triangulation to be 172 metres above sea; +the level of the ground at its foot is unknown, but is probably not +very much above the sea-level, so that Jordan’s estimate of the +height of some of the dunes in the “sand sea” is probably by no +means an exaggerated one.</p> + +<p>Much has been written about eddies in connection with +dune-formation. The only observations I have made in this +connection have been when endeavouring to place temporary marks on +dunes to form survey-points; and the observations seem to show that +if eddies are artificially created at the top of a dune, a rapid +lowering of the dune-crest results. At first I used to thrust a +walking-stick or ranging-rod some 2 or 3 feet into the dune-crest. +The stick or rod, though quite firmly fixed at first, was always +found after a few hours lying halfway down the dune-slope. The same +thing happened with tripods firmly pressed down into the crest. +When I was carrying out a little triangulation to determine the +position of Rohlfs’ cairn at Regenfeld in 1924, I had occasion to +place a mark on a high dune, and I used an empty 4-gallon petrol +tin filled with sand, bedding it well into the dune; but the next +day it had disappeared from the crest, and was found, as the other +things had been, halfway down the slope. These observations remind +me of Mr. Barclay’s description of the method of dealing with +sand-accumulations in the Peruvian Desert,<a id= +"FNanchor_49"></a><a href="#Footnote_49" class="fnanchor">[49]</a> +where, as soon as dunes appear and threaten to obstruct a railway, +the local inhabitants turn out and scatter pebbles and stones on +the dunes, and very soon the dunes are gone, having been carried +away owing to eddies produced by the wind around the stones. This +device for removing incipient dunes might, I think, be tried along +the Kharga Railway, where the screens put up at Mr. Harding King’s +suggestion have not been entirely successful in preventing the +encroachment of sand on the line. I am the more disposed to think +an experiment of this kind might succeed, because I have noticed +that at the gap in the Ramak dunes (discovered by Col. Partridge +and known during the war as “Partridge Gap”) there are great lumps +of silicified wood, which may have led to the gap being formed.</p> + +<p>There are two other physical characteristics of dunes which I do +not remember having seen mentioned. One of these is their low +thermal conductivity. On a hot day, one has only to thrust one’s +hand a few inches into a dune to encounter cool sand, while on a +bitterly cold day one can warm one’s hands by the same action; thus +while the diurnal<span class="pagenum" id="Page_216">[216]</span> +variation of temperature of the surface of a dune is frequently +very great, it is almost insensible at quite a shallow depth in the +interior. It follows that diurnal expansion and contraction of the +grains composing the dune must be confined to the superficial +layers, and the movements thereby caused may materially assist in +consolidating the dune, by causing a “packing” of the grains. The +other characteristic I have noticed is that the surfaces of the +dunes always appear to be harder underfoot in the cool of the early +morning than in the heat of the day. This may, of course, be an +illusion owing to one’s being less sensitive to fatigue in the +early morning, when one’s body has been refreshed by sleep, and +when the air-temperature is comfortable; but I have often fancied +there is more in it than that, and it may easily be that the +“packing” which has taken place owing to the considerable fall of +temperature in the night, to say nothing of the action of dew, may +have caused a real compacting of the surface layers.</p> + +<p>In his paper of 1910, Mr. Beadnell considered that the sand +composing the dunes must be derived from arenaceous formations to +the north, and he made special mention of the need for a careful +survey of the region in which the dunes originate. A reference to +the map will show how correct was Mr. Beadnell’s surmise, at least +in the case of the Egyptian dunes which he had studied. The dunes +originate in the great depressions which stretch from Siwa to the +Wadi Natrun, where, as Mr. Beadnell inferred, the supply of +arenaceous material from the loosely compacted Miocene and +Oligocene beds is almost inexhaustible. We have here one of the +clearest possible examples of the powerful action of the wind as an +excavating and transporting agent. The Qattara depression has been +excavated, largely by the wind, to a depth of over 130 metres below +sea-level, and the excavated material has been carried southwards, +some of it for nearly 1000 kilometres in distance and more than 500 +metres in height, to form the dunes. We see not only the excavated +hollow, but also the transported and piled-up arenaceous material +removed from it; and the total quantity of rock thus removed and +re-deposited must amount to hundreds of cubic kilometres.<a id= +"FNanchor_50"></a><a href="#Footnote_50" class= +"fnanchor">[50]</a></p> + +<p>It is noticeable, however, that to the north of the “great sand +sea” of Rohlfs, which extends for an unknown distance westward, the +known depressions are much shallower; and yet the total quantity of +sand in this region is probably greater than that of all the more +easterly dunes put together. The country between Jarabub and Jalo +is however<span class="pagenum" id="Page_217">[217]</span> almost +unexplored, though it is known to be very sandy and to be the +theatre of violent sandstorms. Whether similar deep depressions to +that of Qattara have been excavated along, or to the north of, the +Jarabub-Jalo road, or whether the area of loosely compacted +arenaceous rocks exposed there is so enormous as to have yielded +such a quantity of sand without any very deep depressions being +formed, is a point that can only be cleared up by further +exploration in Cyrenaica.</p> + +<p>We now come to the most puzzling of all the questions connected +with the sand-dunes, namely, why do they persist as sharply defined +long narrow lines in certain places, while the ground elsewhere is +almost absolutely free from sand? As Mr. Harding King puts it, the +dunes appear to have a curious power of collecting all the sand in +the neighbourhood.<a id="FNanchor_51"></a><a href="#Footnote_51" +class="fnanchor">[51]</a> The sheltering effect of ripples in the +dunes, and a “shepherding” effect of winds a point or two off the +normal, have been suggested as possibly affording some explanation +of this apparent collecting-power,<a id="FNanchor_52"></a><a href= +"#Footnote_52" class="fnanchor">[52]</a> but neither of these +suggestions appears to be adequate. I think a more direct +explanation is possible; namely, that the dunes really +<em>have</em> the power of attracting sand from the air, and that +this power is due to the well-known law of attraction between a +conducting surface at zero potential and an electrically charged +body. That air-borne sand-grains in the neighbourhood of a dune may +carry electric charges was shown by Mr. Harding King’s experiments, +recorded in his paper of 1916, and I have since found sand-grains +to carry electric charges of high voltage during sandstorms in +Cairo. As to how the grains become charged with electricity, it can +hardly be due to friction against each other, for the sand is +remarkably uniform in composition, consisting generally of rounded +grains of almost pure silica coated with a thin translucent film of +ferric oxide,<a id="FNanchor_53"></a><a href="#Footnote_53" class= +"fnanchor">[53]</a> and for the production of frictional +electricity it is generally regarded as necessary that the two +bodies which are rubbed together should be of dissimilar +materials;<a id="FNanchor_54"></a><a href="#Footnote_54" class= +"fnanchor">[54]</a> nor is it likely that they are<span class= +"pagenum" id="Page_218">[218]</span> electrified by friction with +the air, for they travel with it. But if the particles are carried +into an upper air-stratum, they will gradually acquire its +potential by conduction; and the ordinary potential gradient in the +air in Egypt is over 100 volts per metre of height.<a id= +"FNanchor_55"></a><a href="#Footnote_55" class="fnanchor">[55]</a> +Hence a sand-particle carried along for some time in the air at a +height of only 20 metres above the ground may become charged to 7 +electro-static units of potential, or 2100 volts; and on +approaching a dune rising to about that height it will be attracted +to the dune, which being in connection with the earth is at zero +potential. The attraction will be very small unless the sand-grain +approaches very closely to the surface of the dune; from some +calculations I have made, a spherical grain of silica half a +millimetre in diameter charged to a potential of 2100 volts will +not be attracted with a force equal to half its own weight until it +approaches within a centimetre of the conducting surface, and the +grain will have to approach within 7 millimetres of the surface +before the attraction is equal to the weight of the grain. But the +important thing to note is that the attraction is independent both +of the sign of the charge and of the direction of the wind which +carries the particle. Another way of looking at the matter is to +consider the probable distribution of the equipotential surfaces in +the air about a dune, as in the diagram below, which represents a +section taken perpendicular to the direction of the wind and to the +axis of the line of dunes:</p> + +<div class="figcenter iw2"> +<figure id="map5"><a href='images/map5.jpg'><img src= +'images/map5.jpg' alt=''></a> +<p class="cp2"><em>Diagram showing suggested distribution of +equipotential surfaces and directions of lines of force in the +neighbourhood of a sand-dune</em> +</p> +</figure> +</div> + +<p>The equipotential surfaces, shown by dotted lines, will be +squeezed together over the dune, and the electric forces, shown by +full lines and arrows, being everywhere normal to those surfaces, +will converge to the dune. Thus the dune will attract any particles +carried by the wind and charged by conduction to the potential of +the air conveying them. If the wind changes its direction, the +attraction will still persist unaltered. Another point worth +mention is that a sand-dune may be far more effective in its +attraction of sand than a rocky ridge of the same size and +shape<span class="pagenum" id="Page_219">[219]</span> would be; for +when the electrified grains approach the surface of the dune, +uncharged grains can rise from the dune to meet them; possibly some +of the dancing of sand-grains which is frequently observable along +the crest of a dune during a wind may be due to this cause.<a id= +"FNanchor_56"></a><a href="#Footnote_56" class="fnanchor">[56]</a> +During violent sandstorms, particles of sand may be whirled aloft +and kept suspended at high altitudes for a period long enough for +them to acquire very high potentials, and a sudden cessation of the +storm may cause them to fall so rapidly that much of the charge may +be retained; in which case, of course, electrical attraction may +cause a very considerable deviation from the purely gravitational +paths of the falling particles, the deviation being always towards +the dune. Since the closeness of the equipotential surfaces and the +mobility of the sand-grains composing the dune are greatest along +the dune-crest, the maximum rate of deposition will be at the top +of the dune, which is also the place where the wind exerts its +greatest action in conveying the sand of the dunes southward. That +the long axes of the lines of dunes do really correspond with the +direction of the prevailing wind is certain, both from Mr. +Beadnell’s observations of wind-direction<a id= +"FNanchor_57"></a><a href="#Footnote_57" class="fnanchor">[57]</a> +and from the fact that the scoring of the limestones in the Libyan +Desert by wind-borne sand coincides in direction with the lines of +dunes.<a id="FNanchor_58"></a><a href="#Footnote_58" class= +"fnanchor">[58]</a> Thus I suggest that while the extension of the +lines of dunes southwards is purely the result of the prevailing +north-north-west wind, their clean-cut character and narrow width +is the consequence of lateral attraction by the dunes themselves on +the flying electrified particles of sand.</p> + +<p>If the hypothesis I have ventured to put forward is regarded as +likely to furnish the true explanation for the formation of the +lines of dunes, I hope that someone possessing the necessary skill +in electrostatic measurement will put it to a crucial test, by +carrying out observations on and near the dunes themselves. If a +number of flying sand-grains could be caught from different levels +in an insulated metallic receiver connected to an electrometer, the +readings of the electrometer would enable the potentials to which +the grains were charged at different levels to be calculated, +provided the electrostatic capacity of the receiving system and the +number and diameter of the grains giving up their +charge<span class="pagenum" id="Page_220">[220]</span> were +measured. Allowance would, of course, have to be made for any +electrification of the receiver by the air, or by uncaught +sand-grains, as well as for losses by imperfect insulation of the +collecting system. In a preliminary experiment of this kind which I +made in Cairo during a sandstorm, leakage from the electrometer was +found to be so great as to vitiate any attempts at accurate +measurement; but I think this particular difficulty could be +overcome with a specially designed apparatus, or that at least the +leakage could be measured and allowed for. The taking of +observations of any kind in dune areas during windy weather is a +most difficult and trying operation, and commonly means, in +addition, a sojourn of some weeks in isolated and otherwise +uninteresting areas. But the advent of the motor-car has so greatly +facilitated communication in the deserts that difficulties of +access are now not so great as they used to be; the south end of +the 35-kilometre line of the Kattania Dunes, for instance, about 90 +kilometres west-south-west of Cairo, which would form an excellent +site for detailed observations, can now be reached by a four or +five hours’ car journey from Cairo instead of the several days’ +journey by camel which was formerly necessary.</p> + +<h2><a id="s12"></a>12. <em>The Distribution of Stone +Implements.</em></h2> + +<p>I have not made any special study of stone implements, nor have +I been able to pay any considerable attention to their collection +during my journeys, having usually found my time very fully taken +up with other matters. I have, however, been much struck by the +wide distribution of stone implements in the desert. I have found +them, for instance, not only in Siwa Oasis and near the wells of +Abu Mungar and Sheb, but also on the plateau between Baharia and +Farafra, on the open desert between Terfawi and Owenat, and to the +south-west of Owenat near the Anglo-French boundary. This wide +range of occurrence, coupled with the finds of Schweinfurth and +others on the plateaux nearer the Nile, inclines me to think that +there is scarcely any part of the Libyan Desert in which stone +implements might not be found by an expedition which would make the +collection and study of them one of its main objects. The likeliest +places in which to search (besides the neighbourhood of old wells +and springs) would appear to be the shores of the various lakes and +around the feet of hills affording shelter from wind and sun; for +it is in such localities that I have most usually come across +implements and pottery. Grinding-stones, often with a sort of stone +rolling-pin, unpolished celts, knives, and arrow-heads are the +principal forms of implement I have met with. Many of the +grinding-stones must have been carried for a considerable distance, +for they are made out of rocks which do not naturally occur in the +localities in which they are found.</p> + +<p>Whether this wide distribution of stone implements would justify +the view of Blanckhenhorn<a id="FNanchor_59"></a><a href= +"#Footnote_59" class="fnanchor">[59]</a> that primitive man lived +on the desert plateaux<span class="pagenum" id= +"Page_221">[221]</span> rather than in the Nile Valley must, I +think, be settled by the further collection of specimens and by a +careful comparison of the forms to be found in the two situations. +In this connection I may remark that the grinding-stones I have +seen in the desert seemed to me to be very similar to those used by +the Nubians of the Nile Valley to-day for grinding corn.</p> + +<h2 class="app"><a id="app"></a>APPENDIX</h2> + +<p class="sch">SOME RECENTLY DETERMINED POSITIONS IN THE LIBYAN +DESERT</p> + +<p>In view of their possible utility in connection with future +exploratory surveys, I give below a list of some of the more +important of the positions which I have recently determined by +astronomical observation in the southern part of the Libyan Desert, +with brief descriptive notes on the places to which they refer. The +observations were made whilst accompanying H.R.H. Prince Kemal el +Din Hussein on his exploratory motor-car expeditions of 1923, 1924, +and 1925. The longitudes of Qasr Farafra, Abu Mungar, Pottery Hill, +and Regenfeld depend on the transport of a box-chronometer; the +others on wireless time-signals from Europe. The positions of peaks +were found by triangulation from the actual observation-spots. The +altitudes of camps are from careful barometric determinations; +those of the peaks depend on trigonometric levelling from the +camps.</p> + +<table class="tless" id="t221"> +<tr> +<th><em>Place.</em> +</th> +<th colspan="3"><em>Lat. N.</em> +</th> +<th class="width2"> +</th> +<th colspan="3"><em>Long. E.</em> +</th> +<th class="width5"><em>Altitude above sea. Metres.</em> +</th> +</tr> + +<tr> +<th> +</th> +<th>°</th> +<th>′</th> +<th>″</th> +<th> +</th> +<th>°</th> +<th>′</th> +<th>″</th> +<th> +</th> +</tr> + +<tr> +<td class="tdl-top hang1">Merga, Camp 600 metres S.W. of west +corner of salt lake. (Lake surface is 17 metres below level of +camp.)</td> +<td class="tdr-bot">19</td> +<td class="tdr-bot">2</td> +<td class="tdr-bot">29</td> +<td> +</td> +<td class="tdr-bot">26</td> +<td class="tdr-bot">18</td> +<td class="tdr-bot">32</td> +<td class="tdr-bot pad-right1">526</td> +</tr> + +<tr> +<td class="tdl-top hang1">Bir Terfawi, Camp close to well and +palms</td> +<td class="tdr-bot">22</td> +<td class="tdr-bot">55</td> +<td class="tdr-bot">12</td> +<td> +</td> +<td class="tdr-bot">28</td> +<td class="tdr-bot">52</td> +<td class="tdr-bot">51</td> +<td class="tdr-bot pad-right1">244</td> +</tr> + +<tr> +<td class="tdl-top hang1">Gebel Kissu, Summit</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">34</td> +<td class="tdr-bot">59</td> +<td> +</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">8</td> +<td class="tdr-bot">26</td> +<td class="tdr-bot pad-right1">1726</td> +</tr> + +<tr> +<td class="tdl-top hang1">Gebel Owenat, highest point</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">54</td> +<td class="tdr-bot">34</td> +<td> +</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">0</td> +<td class="tdr-bot">47</td> +<td class="tdr-bot pad-right1">1907</td> +</tr> + +<tr> +<td class="tdl-top hang1"><span class= +"word-spaced5"> „ </span> <span class= +"word-spaced5"> „ </span> remarkable triple peak</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">53</td> +<td class="tdr-bot">51</td> +<td> +</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">1</td> +<td class="tdr-bot">39</td> +<td class="tdr-bot pad-right1">1718</td> +</tr> + +<tr> +<td class="tdl-top hang1"><span class= +"word-spaced5"> „ </span> <span class= +"word-spaced5"> „ </span> S.W. peak</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">49</td> +<td class="tdr-bot">35</td> +<td> +</td> +<td class="tdr-bot">24</td> +<td class="tdr-bot">53</td> +<td class="tdr-bot">52</td> +<td class="tdr-bot pad-right1">1450</td> +</tr> + +<tr> +<td class="tdl-top hang1">Chunk Hill, Summit</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">52</td> +<td class="tdr-bot">46</td> +<td> +</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">13</td> +<td class="tdr-bot">56</td> +<td class="tdr-bot pad-right1">985</td> +</tr> + +<tr> +<td class="tdl-top hang1">Owenat, Camp 600 metres S.E. of western +spring, on plain at foot of mountain</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">48</td> +<td class="tdr-bot">35</td> +<td> +</td> +<td class="tdr-bot">24</td> +<td class="tdr-bot">51</td> +<td class="tdr-bot">45</td> +<td class="tdr-bot pad-right1">568</td> +</tr> + +<tr> +<td class="tdl-top hang1">Owenat, Camp at mouth of gully, about 800 +metres S.S.E. of eastern springs</td> +<td class="tdr-bot">21</td> +<td class="tdr-bot">53</td> +<td class="tdr-bot">8</td> +<td> +</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">7</td> +<td class="tdr-bot">58</td> +<td class="tdr-bot pad-right1">626</td> +</tr> + +<tr> +<td class="tdl-top hang1">Gebel Kamil, Summit (160 metres above +plain)</td> +<td class="tdr-bot">22</td> +<td class="tdr-bot">16</td> +<td class="tdr-bot">31</td> +<td> +</td> +<td class="tdr-bot">26</td> +<td class="tdr-bot">38</td> +<td class="tdr-bot">11</td> +<td class="tdr-bot pad-right1">800</td> +</tr> + +<tr> +<td class="tdl-top hang1">Regenfeld, Rohlfs’ cairn of 1874, +rediscovered 1924</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">10</td> +<td class="tdr-bot">49</td> +<td> +</td> +<td class="tdr-bot">27</td> +<td class="tdr-bot">24</td> +<td class="tdr-bot">22</td> +<td class="tdr-bot pad-right1">470</td> +</tr> + +<tr> +<td class="tdl-top hang1">Pottery Hill, Summit (39 metres above +plain)</td> +<td class="tdr-bot">24</td> +<td class="tdr-bot">26</td> +<td class="tdr-bot">27</td> +<td> +</td> +<td class="tdr-bot">27</td> +<td class="tdr-bot">38</td> +<td class="tdr-bot">54</td> +<td class="tdr-bot pad-right1">506</td> +</tr> + +<tr> +<td class="tdl-top hang1">Sheb, Camp close to well, 240 metres +N.N.E. of fort</td> +<td class="tdr-bot">22</td> +<td class="tdr-bot">19</td> +<td class="tdr-bot">48</td> +<td> +</td> +<td class="tdr-bot">29</td> +<td class="tdr-bot">45</td> +<td class="tdr-bot">46</td> +<td class="tdr-bot pad-right1">228</td> +</tr> + +<tr> +<td class="tdl-top hang1">Mut, Government Rest-house</td> +<td class="tdr-bot">25</td> +<td class="tdr-bot">28</td> +<td class="tdr-bot">37</td> +<td> +</td> +<td class="tdr-bot">28</td> +<td class="tdr-bot">58</td> +<td class="tdr-bot">24</td> +<td class="tdr-bot pad-right1">119</td> +</tr> + +<tr> +<td class="tdl-top hang1">Abu Mungar, Camp at small ruin, 400 +metres E.S.E. of well</td> +<td class="tdr-bot">26</td> +<td class="tdr-bot">30</td> +<td class="tdr-bot">22</td> +<td> +</td> +<td class="tdr-bot">27</td> +<td class="tdr-bot">35</td> +<td class="tdr-bot">29</td> +<td class="tdr-bot pad-right1">117</td> +</tr> + +<tr> +<td class="tdl-top hang1">Qasr Farafra, Camp E. of village, 200 +metres S.W. of Tomb of Sheikh Dakhil</td> +<td class="tdr-bot">27</td> +<td class="tdr-bot">3</td> +<td class="tdr-bot">26</td> +<td> +</td> +<td class="tdr-bot">27</td> +<td class="tdr-bot">57</td> +<td class="tdr-bot">52</td> +<td class="tdr-bot pad-right1">90</td> +</tr> +</table> + +<p><em>Merga.</em>—To geographers the most important of the new +determinations will undoubtedly be that of the uninhabited oasis of +Merga, which had not previously been visited by a European, and of +which the situation could hitherto only be guessed at from Arab +statements. Merga lies in a shallow depression about 50 metres +deep, broken by sandstone hills and sand-dunes, and +extending<span class="pagenum" id="Page_222">[222]</span> for some +20 kilometres north-east and south-west. The salt-lake, near the +centre of the depression, measures about 300 metres by 150. It is +surrounded by tall rushes and sandhills except at its south-western +end. There are numerous date-palms, both near the lake and at +considerable distances from it, as well as acacia trees and +tamarisk bushes. The neighbourhood of the lake swarms with +mosquitoes. Good and plentiful water was got by shallow digging +about 1 kilometre south-south-east of the observation-spot, and +could probably be obtained by digging almost anywhere in the +depression. It is possible that the names Bidi and Tura el Bedai, +shown with a question mark on some Sudan maps, may refer to +different spots within the same depression. Owing to the +plentifully scattered vegetation, the place cannot easily be +missed, either by travellers passing within several miles of the +lake, or by aircraft; but the landing of aeroplanes in the +neighbourhood of the lake might be difficult owing to the extensive +sand-drifts.</p> + +<p><em>Bir Terfawi.</em>—Scarcely less important than the accurate +fixation of Merga is that of Bir Terfawi, the farthest south-west +of all the Egyptian artesian water-sources hitherto known. It will +be remarked that this latest determination places the well some 22′ +south and 15′ east of the position which I had provisionally +assigned to it from the rough data furnished by Lieut. Moore’s +traverse of 1916.<a id="FNanchor_60"></a><a href="#Footnote_60" +class="fnanchor">[60]</a> A knowledge of the true position of +Terfawi is specially desirable for a traveller who wishes to reach +it, owing to the absence of any conspicuous landmark near it and to +the sandy nature of the surrounding country, which causes tracks to +be soon obliterated. There are numerous sandhills covered with +tamarisk bushes around Terfawi, and a little grazing for camels. +Besides the well at which observations were taken, water was found +by digging in the sand at the foot of some tamarisk mounds about 13 +kilometres farther west, and it is probable that good and plentiful +supplies could be obtained at shallow depths near any of the other +mounds. The palmtrees at Terfawi are few and small, and are less +conspicuous than the tamarisk-bushes. These latter should enable +the place to be easily found by aircraft; but landing would require +some caution owing to the prevalence of drifted sand.</p> + +<p><em>Gebels Kissu and Owenat.</em>—The peaks of these mountains +(especially that of Kissu, because of its isolated character and +sharply marked summit) will form useful points for the connection +of future surveys, being visible from very long distances.</p> + +<p><em>Chunk Hill</em> is a prominent isolated hill, nearly conical +and of dark colour, which forms a good landmark in the broken +country to the east of Gebel Owenat. It rises some 335 metres above +the ground at its foot.</p> + +<p><em>The Springs of Owenat.</em>—Of the two water-sources of +Owenat whose positions are given, the western one is the better, +and is moreover very easy of access, being practically on the level +of the plain which extends southwards from the mountain mass, and +easily discoverable by the numerous animal-tracks converging to it; +it is a pool among great boulders, obviously fed by percolation +through cracks and fissures in the granite mountain which towers +above it. The eastern water-source is less easy of access; it lies +about 1 kilometre up a stony gully, and consists of a series of +pools in the rocky floor of the gully, fed by trickling springs at +the level where the granite is overlain by sandstone. The plain to +the south of the western spring would form an excellent +landing-ground for aircraft.</p> + +<p>Whilst in the neighbourhood of Owenat, I had hoped to +re-determine the<span class="pagenum" id="Page_223">[223]</span> +longitude of Hassanein Bey’s camp of 1923 with the aid of wireless +time-signals, or at least by triangulation-connection to one of my +observation-points, because a really accurate fixation of the +longitude of a point about midway along his route from Jarabub to +Furawia would possibly furnish the means of slightly correcting the +longitudes assigned to Hassanein’s camps at Kufra and Erdi. I was +unfortunately prevented from carrying out the desired connection; +but from a hurried car-traverse which I made, skirting the western +side of the mountain mass, in the course of which I must have +passed pretty close to the site of Hassanein’s Owenat camp, I think +that camp really lies about in longitude 24° 49′, or some 5 miles +to the west of where I had previously calculated it to be from +Hassanein’s traverse data;<a id="FNanchor_61"></a><a href= +"#Footnote_61" class="fnanchor">[61]</a> and that in consequence +the longitudes assigned to Kufra and Erdi from the same data may be +some 2 or 3 miles too great.</p> + +<p><em>Gebel Kamil</em> is a sharply pointed hill of dark +sandstone, forming a useful landmark between Terfawi and Owenat. It +was visible from the east for more than 40, or from the west for +about 20, kilometres. The name was given to it by Prince Kemal el +Din in honour of his father, Hussein Kamil, the late Sultan of +Egypt.</p> + +<p><em>Regenfeld</em>, it will be remarked, was found to be very +nearly in the position assigned to it by Jordan in 1876,<a id= +"FNanchor_62"></a><a href="#Footnote_62" class="fnanchor">[62]</a> +and my estimation of the level of the place is only 20 metres +higher than Jordan’s. The neighbouring dune I found to be 30 metres +high, agreeing exactly with Jordan’s measurement of fifty years +previously; and as far as I could judge, the situation of the dune +relative to the cairn seems to have remained unchanged through this +long interval, showing that there has been at any rate no great +lateral displacement of the dunes. The iron tanks left by Rohlfs +were quite intact, in spite of their half-century of exposure; they +had become covered with a hard dark brown film, apparently of +magnetic oxide of iron, not rusted in the ordinary way, a fact +which speaks strongly for the dryness of the region. Empty +wine-bottles left by the Rohlfs expedition were frosted by the +sand-blast wherever they were exposed; but surprisingly little of +the glass had been removed in this way.</p> + +<p><em>Pottery Hill</em> is the northern one of a pair of nearly +conical dark sandstone hills about 40 metres high, which are +conspicuous from some distance owing to their situation on a nearly +level sand-plain. I gave it its name from the numerous jars which I +discovered at its foot in 1917.</p> + +<p><em>Sheb Well</em> is a pool of fairly good water in a shallow +excavation at the foot of a clump of dom palms, half surrounded by +sand-dunes and tamarisk mounds, 240 metres north-north-west of a +fort; the latter occupies a fairly conspicuous position on a +sandstone hill about 25 metres high. Another well, situated at the +foot of a clump of dom palms about 11 kilometres farther north, is +called Bir Terfau; this should not, of course, be confused with the +Bir Terfawi already mentioned.</p> + +<p>To the north of Sheb, on the Arbain road, are three other +water-sources which I visited in 1925 and of which I determined the +approximate positions by a carefully controlled car-traverse: Bir +Kassaba, in lat. 22° 41′, long. 29° 55′; Bir Abu Hussein, in lat. +22° 53′, long. 29° 55′; and Bir Murr, in lat. 23° 22′, long. 30° +5′. Bir Kassaba is a pool of good water at the foot of a clump +of<span class="pagenum" id="Page_224">[224]</span> palms; Bir Abu +Hussein, which likewise yields good water, is a small excavation in +sand near a hill of pink coarse-grained granite, and usually +requires to be dug out afresh by each traveller; Bir Murr, on a +little plain surrounded by hills, consists of several holes, with +fairly good water, excavated in the sand at the south side of the +outcrop of a steeply inclined bed of speckled calcareous +sandstone.</p> + +<p>I have not myself traversed the desert to the east of Sheb, but +according to an intelligent Arab who has recently made the journey +from Sheb to Dungul, there are only two spots between these places +at which water is obtainable; they are Bir Abu Seifa, a small well +of good water about 50 kilometres from Sheb, and Bir Haleifa, about +15 kilometres farther on, where there is a fort and numerous wells. +This latter place must, I think, be the same as the Bir Nakhlai, of +which the position found astronomically by Colonel Talbot in 1893 +was lat. 22° 29′ 1″, long. 30° 19′ 36″.</p> + +<p><em>The Rest-house at Mut</em>, in Dakhla Oasis, is a low +whitewashed building of three rooms, situated on open ground a +little to the south of the village. It is conspicuous by reason of +its isolation from other buildings, and forms a convenient +starting-point for car journeys to the south-west of Dakhla, as +well as for journeys to Kharga by the southern track which was +mostly followed by cars during the war.</p> + +<p><em>Abu Mungar</em> proved to be very close to the position +given by Mr. Harding King’s observations of 1912.<a id= +"FNanchor_63"></a><a href="#Footnote_63" class="fnanchor">[63]</a> +To the south-east of Abu Mungar, about halfway to Dakhla, are two +remarkable hills forming outliers of the plateau. These hills, +which are good landmarks, were first discovered by Mr. Harding +King, and as they appear to possess no native name, I have called +them “King’s Hills” on the map. The farther one of the two from the +plateau lies in lat. 25° 58′, long. 28° 11′, from compass-bearings +which I took to it on a careful car-traverse in 1924. The other is +about 2 kilometres farther north.</p> + +<p><em>Qasr Farafra.</em>—The position of the village of Qasr +Farafra which I gave in my paper of 1919<a id= +"FNanchor_64"></a><a href="#Footnote_64" class="fnanchor">[64]</a> +is proved to be very nearly correct by the latest observations. The +main advantage of the new determination is that it is referred to +an easily identifiable landmark, the tomb of Sheikh Dakhil, instead +of to the ill-defined centre of the village.</p> + +<p><em>Levels in or near Baharia Oasis.</em>—I think it may be well +to record here that owing to an unfortunate mistake about the datum +to which the level of the old military railway-terminus at B6 was +referred, all the altitudes given on pp. 10 and 11 of my +above-mentioned Survey Department Paper of 1919 require a +correction of 19 metres to be added. At the time when I +triangulated Baharia in 1917, I was informed that the level found +by the military authorities for the terminus was measured from the +sea-level datum, and I employed the value given for it as my +fundamental level. But I have since ascertained that an arbitrary +datum was employed by the military engineers; and trigonometric +levelling from the Nile Valley has shown that this arbitrary datum +was about 19 metres above sea-level.</p> + +<div class="footnotes"> +<h2 class="fthead">FOOTNOTES:</h2> + +<div class="footnote"> +<p><a id="Footnote_1"></a><a href="#FNanchor_1"><span class= +"label">[1]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_2"></a><a href="#FNanchor_2"><span class= +"label">[2]</span></a>Kindly communicated by Mr. A. R. Boyce, +Director of Sudan Surveys.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_3"></a><a href="#FNanchor_3"><span class= +"label">[3]</span></a>Printed by the French Army Staff, 1926.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_4"></a><a href="#FNanchor_4"><span class= +"label">[4]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_5"></a><a href="#FNanchor_5"><span class= +"label">[5]</span></a>A similar ambiguity of meaning very commonly +attaches to Arabic geographical terms. Thus <em>beled</em> may mean +either a village or an entire country; <em>gebel</em>, either a +mountain or a desert; <em>gezira</em>, either an island or a part +of the Nile bank which is alternately covered and uncovered by the +rise and fall of the river; <em>bir</em>, which properly signifies +a well, is often used to denote a spring or a water-cistern; +<em>wadi</em>, though its proper meaning is a valley, is also +sometimes employed for a closed-in depression, as in the case of +the Wadi Natrun.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_6"></a><a href="#FNanchor_6"><span class= +"label">[6]</span></a>‘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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_7"></a><a href="#FNanchor_7"><span class= +"label">[7]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_8"></a><a href="#FNanchor_8"><span class= +"label">[8]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_9"></a><a href="#FNanchor_9"><span class= +"label">[9]</span></a>‘Zeitschrift der Gesellschaft für Erdkunde zu +Berlin,’ 1902, Tafel III.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_10"></a><a href="#FNanchor_10"><span class= +"label">[10]</span></a>‘Topography and Geology of the Fayum +Province of Egypt’ (Cairo, 1905), p. 67.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_11"></a><a href="#FNanchor_11"><span class= +"label">[11]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_12"></a><a href="#FNanchor_12"><span class= +"label">[12]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_13"></a><a href="#FNanchor_13"><span class= +"label">[13]</span></a>‘Report on the Administration of the +Irrigation Department for 1895’ (Cairo, 1896), pp. 25-28.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_14"></a><a href="#FNanchor_14"><span class= +"label">[14]</span></a>‘Report on the Administration of the +Irrigation Department for 1896’ (Cairo, 1897), p. 129.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_15"></a><a href="#FNanchor_15"><span class= +"label">[15]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_16"></a><a href="#FNanchor_16"><span class= +"label">[16]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_17"></a><a href="#FNanchor_17"><span class= +"label">[17]</span></a><em>Geogr. Journ.</em>, 56 (1920), pp. 97-99 +and 161-163.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_18"></a><a href="#FNanchor_18"><span class= +"label">[18]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_19"></a><a href="#FNanchor_19"><span class= +"label">[19]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_20"></a><a href="#FNanchor_20"><span class= +"label">[20]</span></a>See Appendix III. in the second volume of +Willcocks’ ‘Egyptian Irrigation,’ 1913, p. 853.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_21"></a><a href="#FNanchor_21"><span class= +"label">[21]</span></a>Schweinfurth (<em>op. cit.</em>, 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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_22"></a><a href="#FNanchor_22"><span class= +"label">[22]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_23"></a><a href="#FNanchor_23"><span class= +"label">[23]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_24"></a><a href="#FNanchor_24"><span class= +"label">[24]</span></a>‘An Egyptian Oasis’ (London, 1909), p. +156.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_25"></a><a href="#FNanchor_25"><span class= +"label">[25]</span></a>“The Mutual Interference of Artesian Wells,” +<em>Geol. Mag.</em> (London, 1909), pp. 23-26; also ‘An Egyptian +Oasis,’ chap. x.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_26"></a><a href="#FNanchor_26"><span class= +"label">[26]</span></a>‘An Egyptian Oasis,’ p. 140.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_27"></a><a href="#FNanchor_27"><span class= +"label">[27]</span></a>‘Drei Monate in der libyschen Wüste’ +(Cassel, 1875), p. 115.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_28"></a><a href="#FNanchor_28"><span class= +"label">[28]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_29"></a><a href="#FNanchor_29"><span class= +"label">[29]</span></a>See Rohlfs’ ‘Drei Monate in der libyschen +Wüste’ (chapter ix. of which was written by Ascherson), p. 250.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_30"></a><a href="#FNanchor_30"><span class= +"label">[30]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_31"></a><a href="#FNanchor_31"><span class= +"label">[31]</span></a>See Jordan’s ‘Physische Geographie und +Meteorologie der libyschen Wüste’ (Cassel, 1876), p. 215.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_32"></a><a href="#FNanchor_32"><span class= +"label">[32]</span></a>‘Kharga Oasis’ (Cairo, 1900), p. 57.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_33"></a><a href="#FNanchor_33"><span class= +"label">[33]</span></a><em>Geogr. Journ.</em>, 42 (1913), p. 283; +also ‘Mysteries of the Libyan Desert’ (London, 1925), p. 304.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_34"></a><a href="#FNanchor_34"><span class= +"label">[34]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_35"></a><a href="#FNanchor_35"><span class= +"label">[35]</span></a>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 +(<em>Geogr. Journ.</em>, 56 (1920), p. 259) records that the +sandstone at Ennedi proved to be of Upper Silurian age by the +fossils found in it.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_36"></a><a href="#FNanchor_36"><span class= +"label">[36]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_37"></a><a href="#FNanchor_37"><span class= +"label">[37]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_38"></a><a href="#FNanchor_38"><span class= +"label">[38]</span></a>Quoted in Müller’s edition of Ptolemy’s +Geography, p. 739.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_39"></a><a href="#FNanchor_39"><span class= +"label">[39]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_40"></a><a href="#FNanchor_40"><span class= +"label">[40]</span></a>‘Manual of Ancient Geography’ (London, +1891), p. 311.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_41"></a><a href="#FNanchor_41"><span class= +"label">[41]</span></a><em>Geogr. Journ.</em>, 56 (1920), p. +94.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_42"></a><a href="#FNanchor_42"><span class= +"label">[42]</span></a>‘Mysteries of the Libyan Desert’ (London, +1925), p. 303.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_43"></a><a href="#FNanchor_43"><span class= +"label">[43]</span></a><em>Geogr. Journ.</em>, 43 (1924), p. +288.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_44"></a><a href="#FNanchor_44"><span class= +"label">[44]</span></a>‘The Secret of the Sahara—Kufara’ (London, +1921), p. 235.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_45"></a><a href="#FNanchor_45"><span class= +"label">[45]</span></a>Beadnell, “The Sand-dunes of the Libyan +Desert,” <em>Geogr. Journ.</em> 25 (1910), pp. 379-395; Harding +King, “The Nature and Formation of Sand Ripples and Dunes,” +<em>Geogr. Journ.</em>, 47 (1916), pp. 189-209; Harding King, +“Study of a Dune Belt,” <em>Geogr. Journ.</em>, 51 (1918), pp. +16-33, and Discussion, pp. 250-258.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_46"></a><a href="#FNanchor_46"><span class= +"label">[46]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_47"></a><a href="#FNanchor_47"><span class= +"label">[47]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_48"></a><a href="#FNanchor_48"><span class= +"label">[48]</span></a>See Jordan’s notes on pp. 204 and 208 of his +“Physische Geographie und Meteorologie der libyschen Wüste,” +Cassel, 1876.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_49"></a><a href="#FNanchor_49"><span class= +"label">[49]</span></a><em>Geogr. Journ.</em>, 49 (1917), p. +55.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_50"></a><a href="#FNanchor_50"><span class= +"label">[50]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_51"></a><a href="#FNanchor_51"><span class= +"label">[51]</span></a><em>Geogr. Journ.</em>, 47 (1916), p. +209.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_52"></a><a href="#FNanchor_52"><span class= +"label">[52]</span></a><em>Geogr. Journ.</em>, 51 (1918), p. +252.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_53"></a><a href="#FNanchor_53"><span class= +"label">[53]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_54"></a><a href="#FNanchor_54"><span class= +"label">[54]</span></a>Professor P. E. Shaw has quite recently +(<em>Nature</em>, vol. 118 (1926), p. 659) suggested from +laboratory experiments that the mutual <em>impact</em> of particles +of <em>identical</em> 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).</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_55"></a><a href="#FNanchor_55"><span class= +"label">[55]</span></a>Hurst, <em>op. cit.</em>, p. 28.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_56"></a><a href="#FNanchor_56"><span class= +"label">[56]</span></a>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?</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_57"></a><a href="#FNanchor_57"><span class= +"label">[57]</span></a><em>Geogr. Journ.</em>, 35 (1910), p. +385.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_58"></a><a href="#FNanchor_58"><span class= +"label">[58]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_59"></a><a href="#FNanchor_59"><span class= +"label">[59]</span></a><em>Zeitschrift der Gesellschaft für +Erdkunde zu Berlin</em>, 1902, p. 760.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_60"></a><a href="#FNanchor_60"><span class= +"label">[60]</span></a>‘Recent Determinations of Geographical +Positions in the Libyan Desert,’ Survey Department Paper No. 34, +1919. p. 14.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_61"></a><a href="#FNanchor_61"><span class= +"label">[61]</span></a><em>Geogr. Journ.</em>, 44 (1924), p. +377.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_62"></a><a href="#FNanchor_62"><span class= +"label">[62]</span></a>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.</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_63"></a><a href="#FNanchor_63"><span class= +"label">[63]</span></a>Mr. Harding King’s observations gave the +latitude as 26° 30′ 46″, and the longitude as 27° 36′ (see his map +in <em>Geogr. Journ.</em>, 42 (1913), p. 516).</p> +</div> + +<div class="footnote"> +<p><a id="Footnote_64"></a><a href="#FNanchor_64"><span class= +"label">[64]</span></a>‘Recent Determinations of Positions in the +Libyan Desert,’ Survey Department Paper No. 34 (Cairo, 1919), p. +12.</p> +</div> +</div> +</div> +<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 77091 ***</div> +</body> +</html> + |