9. Can Travel in the Great Tracts of the Libyan Desert which are now Waterless be facilitated by the Sinking of New Wells?

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.

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.

As regards the first of these conditions, we know that the water-bearing beds underlying the Libyan Desert are situated within the geological 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.

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.

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 viâ 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.[35] Gebel Kissu probably resembles the south-western part of Owenat in being entirely composed of crystalline rocks.[36] 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.

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.

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.