There appears originally to have been a colonnade between the first and second pylons, but only fragments of the columns exist at the present day. The front of the forecourt is covered with hieroglyphics, while the interior is unsculptured except at the portal leading to the main hall, the latter measuring 6 by 5½ metres, and having four columns. On the west side there is an entrance leading to an inclined passage. The northern part of the building consists of a central semi-divided portion flanked by two elongated chambers, all of which have arched roofs. A parapet is formed by the external walls of the temple, while the roof over the three southern chambers is at a lower level than that of the main hall.
THE TEMPLE OF HIBIS (INTERIOR).
The temple proper is in the western portion of an immense rectangular enclosure bounded by very thick walls of sun-dried brick; these walls at the present day are in a very bad state of preservation, but appear to have been of the type common in some similar buildings in the north of the oasis— i.e., hollow at the top, so as to enclose a passage by means of which the custodians could make the circuit of the building without descending, and from which, unobserved from the exterior, they had the advantage of a splendid view of the surrounding country. The measurements and details which I have given above are largely taken from Dr. Ball’s report, to which the reader is referred for plans and sections of this and other temples.
One of the most conspicuous ruins in the oasis is the little temple of Nadûra, situated on a hill 1 kilometre south-east of the temple of Hibis. The inner building is of sandstone, and roughly measures 8 by 11 metres, while the outer portion, bounded by walls of unburnt brick, is very much larger. According to Sayce, the temple was built by Hadrian between A.D. 117 and A.D. 138. Brugsch, however, refers it to a somewhat later date, considering it to have been erected by Antoninus Pius. Several smaller ruins in the neighbourhood are probably referable to the same period as the temple itself.
The ruins of Qasr Zaiyan, 5½ kilometres north-east of Bulaq, enclose a small sandstone temple of somewhat doubtful age, though a Greek inscription over the entrance records that the building was restored by Antoninus Pius and dedicated to Amenebis (Ammon of Hibis), god of Tchonemyris, the ruins of which town exist in the vicinity. The inscription is translated by Hoskins as follows:
The Emperor Antoninus Pius reigned from A.D. 138 to A.D. 161, but antiquities unearthed from the ruins show that the town dates from the time of the Ptolemies and flourished into the Byzantine period.
In addition to the above the dilapidated ruins of what were doubtless once imposing buildings exist at various points within the depression. One worthy of attention will be noted at Ain Amûr by travellers to Dakhla along the upper road. The exact age of the building is uncertain, though Wilkinson discovered thereon a portion of the name of one of the Cæsars. The small stone temple stood, like so many others in the oasis, in a courtyard enclosed by thick walls of unburnt brick, the fragmentary remains of which are visible in the illustration. The names of the principal deities inscribed on the temple walls are Kneph, Ammon, and Mut. Both Edmonstone and Wilkinson came to the conclusion that the temple is of greater antiquity than the majority of the monuments of the oasis; but I am inclined to believe, with Hoskins and Rohlfs, that its somewhat crude design is explicable on other grounds than that of age.
Perhaps the most remarkable and imposing buildings in the oasis are the great Roman fortresses, among which may be mentioned Um el Dabâdib, Qasr Lebekha, and Dêr el Ghennîma. Possibly some of these were fortified monasteries, though until the ruins, as well as those of the extensive towns and cemeteries which existed in the neighbourhood, have been subjected to critical examination, their exact nature must remain in doubt. The so-called Dêr, near the foot of Jebel Ghennîma, was certainly a fort guarding one of the chief passes up the escarpment of the oasis. It is built of immensely thick walls, strengthened intermediately and at the four corners by enormous buttresses. The walls taper slightly upwards, and at the top are double, concealing a passage which ran round the entire building. In the centre of the court was a deep bore from which the inmates obtained their water, the surplus supply flowing through an underground conduit to the cultivated lands outside.
Qasr Lebekha, situated in a lonely part of the depression under the northern escarpment, 12 kilometres north-west of Meheriq, has many points in common with the fortress just described. It is, however, much smaller, and its interior is completely filled with domed chambers, now falling into shapeless fragments.
The impressive ruin at Um el Dabâdib, 36 kilometres N.N.W. of Kharga, seems to me to have been a fortified monastery, the interior being filled with vaulted cells. Its appearance is quite distinctive, lacking as it does the round buttresses of Qasr Lebekha and Dêr el Ghennîma, though the walls are still of great thickness, and loopholed for defence. Outside are the remains of a town of considerable size, and here doubtless several hundred workmen were quartered when the extensive subterranean waterworks, which exist in the locality, were in course of construction.
A fourth large ruin, of somewhat similar architecture, occupies a conspicuous position on the edge of the escarpment overlooking the Bellaida district, about 2 kilometres north of the temple of Hibis. Ball describes this under the name of Qasr Ain Mustapha Kashef, a name which, of course, merely refers to its position near a well of that name. The interior consists of tiers of arched chambers, and according to Schweinfurth there is little doubt that the building was a monastery.
All the above-mentioned forts and monasteries are built of large sun-dried bricks measuring, as a rule, 35 × 17 × 9 centimetres, and it is noteworthy that the walls, where of exceptional thickness, were built in sections, perhaps to allow of their drying more readily. Besides those described, a great many other mud-brick buildings are to be found scattered through the oasis, the majority of which possess no very distinctive features. One, however, being sure to attract the attention of visitors may be specially referred to; this is a high rectangular tower occupying a very conspicuous position on the open plain to the west of Jebel Têr, measuring 5 by 6½ metres at the base, the walls tapering slightly upwards to a height of about 15 metres. It was originally divided into storeys and provided with a staircase, and may very probably have been used as a watchtower. The remains of a circular brick or pottery kiln are to be seen twenty paces to the south.
The exact age of these numerous brick buildings cannot be stated with certainty, and we can only hope that when the pottery, coins, and other objects which exist in the ruins of the adjoining towns have been systematically collected and examined, it may be possible to date them with more accuracy. At present we can only conjecture that while the greater number were erected during the Roman occupation, between 30 B.C. and A.D. 395, some of them may date from the succeeding Byzantine period. Many of the cemeteries contain mummy-cases on which the likeness of the deceased is carved in wood on the outside, or fashioned in stucco and painted in colours. Three of these from an ancient burial-place in the Bellaida district, between Jebel Têr and Jebel Tarif (one of a number of cemeteries of Roman age which await the attention of archæologists), are shown in one of our illustrations.
THE CHRISTIAN NECROPOLIS.
Christianity was introduced into Egypt in the early part of the Roman domination, and spread rapidly through the country, although the national Egyptian or Coptic Church was not established until A.D. 451. Judging by the size and importance of the cemetery at the south end of Jebel Têr, and by the numerous monasteries, Christianity must have had a great following in the oasis of Kharga. During this period many of the temples in Upper Egypt were converted into churches, and it was not until A.D. 640, when the Caliphs conquered the country, that Christianity began to wane.
The Christian Necropolis lies 1 kilometre north of the temple of Hibis, on the southern extremity of the foot-hills of Jebel Têr. The cemetery, known at the present day as ‘El Baguat,’ consists of a great number of tombs built of unburnt brick, the majority showing a considerable amount of architectural decoration. The buildings cover a large area, and are to a certain extent laid out in streets, which, as Ball remarks, give the place the appearance more of a strange deserted town than of a graveyard. Some are small tombs, noticeable for their simple beauty; others are large mausolea and sanctuaries, richly ornamented with columns, pilasters, and arches. Almost without exception the tombs are surmounted by domes, though, owing to the walls being carried up beyond the base of the dome, the latter is not always conspicuous from the outside.[6] The interior walls are invariably plastered and whitewashed, and covered with numerous Greek and Arabic inscriptions, the old Egyptian ‘Tau,’ the sign of eternal life, being frequently displayed. In addition, the walls and domes are in some cases ornamented with crude coloured designs. The pictures have, unfortunately, been mostly hacked to pieces or covered by Arabic writings, so that there are now only two tombs in which the original paintings are anything like intact. On the dome of one of these, near the south end of the cemetery, a number of familiar Biblical personages are represented in colours, their names being inscribed in Greek characters immediately above. Adam and Eve, Noah, Abraham, Sara and Isaac, Christ, Paul, and others are clearly distinguishable.
The actual grave is below the centre of the floor of each tomb. The bodies, which mostly appear to have been embalmed and wrapped in cloth, have in many cases been plundered of ornaments and thrown out. Even at the time of Hoskins’ visit in 1837 the majority of the tombs had been ransacked, and at the present day there are probably few left intact. With regard to the practice of embalming, Hoskins writes: “It is highly satisfactory that we have such indubitable evidence to enable us to establish the fact, that the custom of embalming the dead was continued by the first professors of the Gospel in Eastern Africa. The introduction of Christianity produced great and sudden changes in the minds, habits, and customs of believers; but a length of time was no doubt often necessary to root out many of the prejudices of the people; and it is very possible, that the practice of embalming may have been continued as a necessary mark of respect to the dead, long after the doctrine had been entirely exploded, in accordance with which the custom had been originally established. This practice, however, even in the most ancient times, was not confined to the worshippers of Amun. The physicians of Egypt were forty days in embalming Jacob; and Joseph also was embalmed in Egypt.”
BIBLICAL SCENES IN A TOMB OF THE NECROPOLIS.
We cannot speak with certainty as to the exact period during which this cemetery was in use. In the course of the reign of Constantius (337-361), Athanasius, the champion of the doctrine of the Trinity, was several times expelled from Alexandria and compelled to take refuge in the Libyan Desert, where there were numerous monasteries, which afforded safe asylums from the followers of Arianism and Paganism. Hoskins states that the name of Athanasius occurs in one of the Theban sepulchres, and he believes that “the ruined monasteries in the Oasis Magna were, probably, the abode of the great champion of the Christian religion.”
During the reign of the Emperors Arcadius and Honorius numerous personages, including the general Timasius, were exiled to the Great Oasis, described by a writer (Zosimus) as “a barren place whence no one could escape when once carried thither; for the way being sandy, desert, and uninhabited, no one can find it, the wind covering the traces of people’s feet, nor is there any tree or house to guide them.”
Nestorius, Bishop of Constantinople, was excommunicated and banished to the oasis in A.D. 434 by the Patriarch Cyril of Alexandria, and probably the necropolis contains the tombs of a large number of his followers. The Bishop, however, did not die in Kharga, as he was carried thence into captivity by the Blemmyes, the ancestors of the Bisharin and Ababdeh Arabs, and died, after suffering great persecutions, at Panopolis (Akhmîm) about the year 440. It is interesting to note that certain Christian customs and festival days are still observed in the oasis at the present time.
Ruins of columbaria are of frequent occurrence in many parts of Kharga, and judging from the size and shape of the bricks used, belong to the same period as the forts and monasteries. They are generally of considerable size, the inner walls being built so as to provide tiers of cubical niches to serve as nesting-places for the pigeons. Examples may be seen at Ain el Burg and Ain Tabashîr in the Meheriq district; in the Bellaida country, and near Ain Khenâfish; on the slopes of the Gorn el Gennâh; and near the village of Dush at the south end of the oasis. These ancient pigeon-houses are called ‘Burg’ by the natives, the Arabic name for dovecot being ‘Burg Hamâm.’
That the oases were very flourishing under the Roman Empire is shown by Olympiodorus, who lived in the reign of Theodosius II. (A.D. 408-450), and was born in Upper Egypt. Writing of the Great Oasis, he calls attention to its salubriousness, to the abundance of sand everywhere, and to the numerous wells, which, sunk to a depth of 200, 300, or even 500 cubits,[7] pour forth streams of fresh water at the surface, which is used in rotation by the owners for the irrigation of their fields. Barley, he avers, is sometimes sown twice a year, and millet almost always three times. Writing of the irrigation, Olympiodorus remarks that in this region the sky is always cloudless, and that the great fertility of the land is attributable to the fact that the peasants water their little enclosures every third day in summer, and every sixth in winter. The same writer states that dials were made in the oasis.
The presence of marine shells in the rocks of the surrounding deserts led Olympiodorus to conjecture that the oasis was formerly an island, separated by the sea from the rest of Egypt, and he recalls the fact that the place was called by Herodotus ‘the Island of the Blessed.’
Strabo writes of the Libyan Desert thus: “This continent resembles a panther’s skin, as being spotted with inhabited districts, insulated in the midst of a sandy soil and arid deserts; the Egyptians call these cantons ‘Auasis.’” He refers to the Great Oasis as follows: “In a parallel line with Abydus, and distant about three days’ journey across the desert, we find the first of the three Oases of Lybia; it is a spot well inhabited, well supplied with water, and producing wines and other commodities in sufficient abundance.”
With the withdrawal of the Roman garrisons and the Mohammedan conquest decay set in, and, as Sayce remarks, the aqueducts became choked, the fields were neglected, and malarial fever invaded a district which had at one time been regarded as a health resort.
Of the history of the oases during the succeeding seven or eight centuries no records are available, but, judging from the writings of Arabian geographers, between the eleventh and the fifteenth centuries, it is evident that they gradually became depopulated, and were regarded as of little importance. El Sherîf el Edrissi, writing about the middle of the sixth century of the Hegîra, refers to the oases (Al Vahat) as places formerly containing streams of water, with lands on which trees were still found growing, and with ruined, uninhabited towns. He adds that the goats and sheep had become quite wild, and were trapped by hunters like other wild animals. It is not improbable, however, that this author was referring to some of the smaller oases-depressions, such as Kurkur, or perhaps to some of the more outlying parts of Kharga or Dakhla. It seems extremely unlikely, as Hoskins remarks, that the Great Oasis as a whole had become entirely uninhabited.
Still later the emir and historian Ismail Abulfida, about the beginning of the fourteenth century, speaks of the oases as abounding with palms and running water, and describes them as situated like islands, in the middle of the desert, three days’ journey from the Said (Upper Egypt). Jacutus describes the positions of three oases, and refers to the first of them as being well cultivated, containing streams and hot springs, palms and cultivated lands. The inhabitants, he adds, are in a wretched state. Several other writers allude to the Egyptian oases, but their information is seldom, if ever, first hand, and the descriptions are in general so vague that we are left in doubt as to which particular oasis their remarks refer.
The more modern records, commencing with those of Poncet at the end of the seventeenth century, have already been referred to in a previous chapter.
CHAPTER VIII
THE EXTINCT LAKES OF THE
OASIS
Character and Extension of Lacustrine Deposits — Modern Erosion by Wind-borne Sand — The Lakes geologically of Recent Age — Discovery of Pottery and Bones of Domesticated Animals — Area occupied by the Lakes — Maximum Level of their Waters — Lacustrine Strata at Gorn el Gennâh — Relation to the Ancient Monuments — Altitudes of Archæological Sites — Age of the Lakes and their Persistence into Historic Times — Flint Implements — Origin of the Lakes — Their possible connection with the Artesian Waters — Lacustrine Deposits form the Cultivated Lands of Modern Times.
When in 1906 I commenced to make a special study of the geology of the oasis, with a view to elucidating certain questions which had arisen in connection with the water-supply, it came to me as a very great surprise to find indubitable evidence that the greater part of the floor of the depression had at one time or another been the site of an immense lake. No mention had been made by previous observers of the extensive accumulations of lacustrine sediments which cover so large a proportion of the floor, and are found from near Ain el Ghazâl in the north to beyond Beris in the south.
LACUSTRINE DEPOSITS AT EL GALA, NEAR BULAQ.
These deposits consist of horizontal finely-bedded alternations of sand and clay, or more frequently of an intimate mixture of the two; local false-bedding is not uncommon, and included fragments of limestone or sandstone are occasionally met with. The beds have a prevailing brown tint, and frequently exhibit well-marked hexagonally disposed shrinkage cracks. Although originally they must have formed an immense compact and continuous sheet, the deposits have since been subjected to considerable denudation, so that at the present day they exist as large isolated patches. Perhaps the most striking of these is that occupying the centre of the depression between Kharga village and Jebel el Ghennîma, covering an area of between 40 and 50 square kilometres, and over the greater part cut by the sand-blast into thousands of isolated hummocks, disposed with their longer axes parallel and in the direction of the prevailing north winds. Individual hummocks have perhaps an average height of 4 or 5 metres, though many exceed this considerably; in length they may measure anything up to 40 or 50 metres. The northern end of a hummock is in nearly all cases the larger, the gradual tapering towards the south being a most distinctive feature. Their present shape and appearance are, of course, entirely due to the eroding and sculpturing action of sand-laden wind.
The finding of these extensive lacustrine deposits naturally opened up a number of questions of the greatest interest and importance. To what level had the waters of the lake attained; what were its limits horizontally; and, most important of all, at what period had it existed, and what were its relations to the ancient monuments of the oasis? With the object of solving these problems it has been my endeavour to collect all possible information concerning the deposits, and, although it is perhaps too soon to draw inferences with any great certainty, I propose to put on record such data as I have been able to obtain, and to indicate the conclusions to which they appear to lead.
It is, of course, obvious that the lake was, geologically speaking, of comparatively recent date; the lacustrine deposits have nothing in common with those of the Cretaceous and Eocene formations which build up the plateau-massif out of which the oasis-depression is hewn. The sands and clays are much softer and less consolidated beds, laid down superficially and unconformably on the uneven surfaces of the older formations; the depression had, in fact, almost attained to its modern dimensions before the beds in question were formed. My first impression was that the lake dated from prehistoric, if not prehuman, times; that it existed before the prevailing desert conditions set in, when the Nile Valley was the site of extensive lakes and the country was partially wooded. The existence of thick deposits of calcareous tufa on the upper portions of the cliffs of the depression suggested a considerable outpouring of water from springs, and it seemed not improbable that the surplus water collected on the floor of the depression below.
For some time I was unable to discover any clue to the age of the deposits, in the shape of organic remains or human relics. Then, in a pit sunk for surface-water in the neighbourhood of Headquarters,[8] some fragments of pottery were found at the base of the deposit. This discovery was followed by the finding of other pieces of pottery firmly embedded in some of the clay hummocks to the south-west of Headquarters. These were without question in situ, and proved that the lake was contemporaneous with man.
Further search, in which I was greatly assisted by my friend H. H. Baker, M.B., led to the discovery of human settlements, apparently on the margins of the lake. In these localities large quantities of broken pottery were found associated with the bones of domesticated animals, while the fresh-water gastropod shell, Melania tuberculata, was found to be abundant in some of the beds. Careful exploitation of one or two of these sites, about 6 kilometres south-west of Headquarters, enabled us to procure a number of complete earthenware vessels, the chief types of which are shown in one of our illustrations. A comparison of these with pottery of known age must be left until we have referred to the horizontal and vertical extension of the lake.
Judging from the still existing deposits, and utilizing (in the northern part of the oasis) a considerable number of levels, I believe the limits of the lake to have been as shown on the accompanying plan. From its most northerly point in lat. 25° 45′ N., in the neighbourhood of the modern Ain el Ghazâl, its western boundary trended S.S.W., passing about 1½ kilometres west of Meheriq village to the south-west end of Jebel Têr; thence its shore-line lay at the foot of Jebel Tarwan, rounding which it projected somewhat into the Bellaida district between Jebel Têr and Jebel Tarif. South of this it bore slightly west of south, passing about 2½ and 3 kilometres west of Kharga and Gennâh villages respectively. From the latter point the shore-line proceeded almost due south to lat. 25° 2′ N., in the vicinity of Ain Girm Meshîm.
Its eastern limit appears to have been about a kilometre east of Ain el Qasr, and some three times that distance east of Meheriq, so that on this latitude the lake had a breadth of 4½ kilometres. In the neighbourhood of Headquarters its margin lay 2 kilometres to the east, whence it ran almost due south for about 12 kilometres. Here, just to the south-west of Ain Harrân, the lake attained its greatest width—i.e., 15 or 16 kilometres, gradually diminishing southwards to Ain Girm Meshîm. The total length of this portion of the lake was just over 80 kilometres.
Both at Ain Girm Meshîm and Ain el Doum the lacustrine deposits are well seen; over the intermediate country they were not observed, and as this area lies at a somewhat high elevation, it seems probable that there was a break in the continuity of the lake of about 15 kilometres in extent.
The southern portion appears to have measured approximately 45 by 15 kilometres, its long axis lying along a line passing through Ain el Doum, Beris, and Maks Qibli. To the south-east the lake had a local extension in the neighbourhood of Dush. It is thus seen to have extended, with a possible break of a few kilometres in the district near Ain Girm Meshîm, almost throughout the length of the depression, over a distance of 136 kilometres, or 85 miles.
It proved a matter of some difficulty to determine the maximum height to which the lake had reached, as in most localities the deposits have suffered considerable denudation, and their margins are usually obscured by blown sand and superficial detrital material. The pottery to the south-west of Headquarters was ascertained to occur at 47 metres above sea-level, the uppermost limit of the deposits in that area being 62 metres. At Headquarters the lake clays occur up to between 65 and 66 metres; at Ain Terfai and Ain Mahmud, north of Meheriq, to 65 and 67 metres respectively. Still farther north I found there were stretches of similar clays at 76 metres near Ain el Qasr, and at 84 to 85 metres in the neighbourhood of Ain el Ghazâl.
On the west side a very well-defined plain formed of the lake beds occurs immediately to the east of the Necropolis, and was found to lie at 70 metres above sea-level. But the most valuable data of all were those obtained at the Gorn el Gennâh. There, as anticipated, the lacustrine deposits, containing Melania and Limnæa in abundance, were found to be well developed and exposed, being piled up on the flanks of the hill on its north, east, and south sides, the exact limits of the beds being best seen on the south-east side near the ruins of a columbarium. Immediately behind the latter the top of the stratified clays was determined as 66½ metres, a figure agreeing remarkably closely with the majority of the maximum heights farther north. Still higher up, however, are other clays, which, while similar in general appearance, are either very irregularly bedded or altogether unstratified. The upper limit of these clays was found to be 82·76, or, say, 83 metres. While these highest beds may possibly have been deposited by the waters of springs issuing from faults and fissures (the line of disturbance mentioned in a previous chapter passes through the Gorn at this point), one must, in the absence of any definite evidence to the contrary, regard them as probably representing the extreme marginal deposits of the lake.
We may, indeed, conclude that, while the lake presumably at one time reached to a maximum level of 85 metres, it stood for a considerable period at about 70 metres above sea-level.
COFFIN-MASKS FROM BELLAIDA.
ANCIENT POTTERY FROM THE LACUSTRINE DEPOSITS.
The next step was to ascertain the altitudes of the archæological sites and the relation of the latter to the lacustrine deposits. Up to the present time levels have not been carried through to the south end of the oasis, and aneroid determinations are not of sufficient accuracy for our purpose, so that we must confine our attention in this connection to the northern portion of the depression. The ground-level of the temple of Hibis was found to be at 75 metres and the lowest of the tombs of the Necropolis at 80·6 metres above sea-level. The columbarium already alluded to, on the south-east side of the Gorn el Gennâh, is built on the denuded slopes of the lacustrine series at a level of 57·2 metres, while the base of a number of brick ruins a little to the north was found to be just over 53 metres. Finally, the ground-level at the base of the slope on which stands Qasr Zaiyan was determined as 21 metres, a bench-mark being made on the southern door of the temple at 24·52 metres above sea-level.
There are several points in connection with the disposition of the archæological remains which cannot but strike one. In the first place, they are mostly on or near the extreme margin of the lacustrine deposits; secondly, they are absent altogether from the central portion of the lake site; and thirdly, the older monuments occupy the highest levels, while there are no representatives at all of the earlier Egyptian periods. While the disposition of the monuments may, of course, be entirely fortuitous, we are justified, I think, in assuming that the lake existed well into the historic period, and may have still stood at the 65 or 70 metre level when the temple of Hibis was erected by Darius, about 500 years before the commencement of the Christian era. In the time of the Ptolemies it was certainly considerably lower, while in still later days, when the country became a Roman province, the lake had very much contracted, and probably only existed as a marshy swamp occupying the lower portions of the depression.
What age, it may be asked, is indicated by the pottery, bones, and fresh-water shells which, as already mentioned, have been found in the lacustrine deposits? Unfortunately the shells belong to species which have a wide distribution, and have persisted from early Pleistocene times right up to the present day. They do not, therefore, help us to fix the age of the deposits, except within wide limits. The bones were submitted to Dr. Andrews, F.R.S., of the British Museum Staff, and his conclusion is that they belong to two domesticated animals—one a small, lightly-built ox, the other a small horse, donkey, or zebra; unfortunately they are not sufficiently complete to be determined with certainty. Finally, as to the pottery: the types do not differ in any important respect from those associated with the towns and cemeteries of Græco-Roman age in many parts of the oasis. The barrel-shaped pot has, indeed, persisted to modern times, being, in a slightly different design, the standard water-jar at the present day in the oasis of Dakhla. The pottery, therefore, bears out our conclusions that the lake continued to exist well into the historic period.
Although flint implements have never yet been detected in situ in the lacustrine deposits, I have collected a considerable number from the area originally occupied by the lake. Some of these were found lying on the denuded surfaces of the lake beds, in positions which lead me to suppose that they have weathered out from the deposits. They are decidedly Neolithic in workmanship and character, and were, in my opinion, used by people inhabiting the depression at the time of, and probably prior to, the existence of the lake. A number of examples are shown in one of the accompanying plates; the figure in the bottom left-hand corner is, however, that of a palæolith, a typical example of those which occur on the borders of the plateau, and on or near the eastern escarpments. In the right-hand bottom corner is figured an object of very common occurrence in the oasis—a sandstone hand-grinder, probably of Roman age. With the exception of these two the specimens illustrated are all implements from the site of the lake. Flint implements were evidently in use in Kharga at a very late period, as large numbers of worked flints, mostly in the form of flakes or tools of very poor finish, occur near many of the old sanded-up wells. A considerable amount of detailed work will have to be undertaken before the different flints of the oasis can be satisfactorily arranged in chronological order.
From what period did the lake date, and to what cause did it owe its origin, are questions which cannot, I fear, be definitely answered as yet. While it is quite reasonable to consider, in the absence of any decisive evidence to the contrary, that the lake originated in early prehistoric or Pleistocene times—that it dates possibly from the time of the formation of the tufas of the Nile Valley and oasis-escarpment, when the climate was certainly much moister than at the present day—we must not forget the possibility that it was formed by artificial means during one or other of the Egyptian dynasties between 3000 and 1000 B.C.
There is good reason to believe that the depression was inhabited previous to the formation of the lake, and although we have no information as to when the first deep borings were made, there is some evidence which leads me to suspect that wells existed prior to the time when the surface of the lake began to fall, if not very much earlier. The evidence to which I refer is the discovery of a portion of an earthenware pipe embedded in situ in the lake clays at a height of 42·85 metres, of the type used by the ancients for lining their water-channels. Is it possible, therefore, that, as the result of the industry of the ancient well-borers— following their initial discovery of these deep-seated sources—the long-confined waters welled up with irresistible force, and gradually flooded the country. At the present day, when the pressure throughout the artesian basin must be very much less than formerly, it is not uncommon for new bores to get out of control and flood considerable areas of country. The same thing may possibly have happened on a very much larger scale thousands of years ago, when the first bores were sunk into a previously untapped artesian basin, fully charged with water under great pressure.
FLINT IMPLEMENTS.
There is another explanation which it is advisable to keep in mind, though it has never hitherto, as far as I am aware, been advanced as a possible cause of the formation of lakes. The very existence of artesian water depends on the presence of porous strata overlain by impermeable beds. If one or other of the porous beds, charged with water under pressure, should, through the action of denudation on the overlying beds, become exposed at the surface, the waters would escape through natural springs in very large quantities. This might, indeed, continue for a long period of time, until the bed was nearly depleted and the pressure reduced to nil. There is little doubt that the beds which we have named the ‘Surface-water Sandstone,’ and which are now exposed in places on the floor of the oasis, were originally entirely covered by impervious clays, and contained artesian water under pressure; they may, in fact, have been in the same condition as is the Artesian-water Sandstone at the present day. It is conceivable, therefore, that when those beds became exposed at the surface, owing to the removal of the overlying confining strata, their contained waters escaped in such quantities as to have given rise to a lake of considerable dimensions, if not to one equal in size to that which we have been considering.
No one can be more conscious than myself of how much there is still to be learnt regarding the topographical aspects of the oasis in early historic times, and although the theory that the lake may have been formed by waters which escaped from the underlying water-charged beds (either artificially through bore-holes or naturally as springs) may at first sight appear fanciful, it is one which, in the present imperfect state of our knowledge, is at least worth bearing in mind. A more detailed examination of the lacustrine deposits would probably throw further light on the matter; and a minute analysis of the nature, composition, and arrangement of the individual grains would almost certainly show whether the beds have in the main been formed of sediment carried into the lake by streams from the neighbouring cliffs and plateaux, or whether they represent wind-borne accumulations of sand and clay-dust from the surrounding plains.
At whatever period and in whatever manner the lake may have been formed, it is quite clear that it existed well into historic times, and that on its bed were laid down thick deposits of clay and sand, which at the present day form the bulk of the cultivated lands of the oasis.
CHAPTER IX
THE UNDERGROUND
WATER-SUPPLY
The Water-bearing Strata underlying the Libyan Desert — Essential Conditions required to produce an Artesian Basin — The Surface-Water Sandstone — Collecting Pits — Fissures — Yield of Water — Flowing Wells from this Sandstone — Bores at El Dêr el Ghennîma — Variable Quality of Water — Ancient Subterranean Aqueducts — The Artesian-Water Sandstone — General Characters — The Headquarters Area avoided by the Ancients — Drilling Difficulties — Results of New Bores — Factors determining Discharges of Wells — Temperature and Chemical Composition of Artesian Waters.
When laboriously traversing the hot and arid plateaux of the Libyan Desert, our thoughts divided between the fertile plains of the Nile we have left behind and the still far distant oasis, it is difficult to realize the presence, within a distance of a few hundred yards, of an abundant supply of the purest water. Yet there is little doubt that the water-bearing beds underlie practically the whole of the Libyan Desert, though it is only on the floors of the depressions that they lie within accessible distance of the surface. On the high tablelands the cost of sinking bores to reach the sandstones would be prohibitive, and without the aid of powerful and costly pumps the water would not rise to the level of the ground. But although the subterranean waters of the great desert plateaux cannot economically be made available at the surface, it must not be forgotten that the deeply buried sandstones of these regions must act to a great extent as storage reservoirs capable of replenishing the beds underlying the oases-depressions, from which large volumes of water are continuously drawn by the numerous artesian wells.
The essential conditions required to produce an artesian basin, which, when tapped by borings, will produce self-flowing wells, are the presence of strata of sufficient porosity to carry water, enclosed above and below by beds of sufficient impermeability to prevent the escape of that water; the outcrop of the porous beds in some higher and distant region, with an adequate exposure to an abundant source of water, whether rain, river, or lake; and, finally, the absence of an easy escape at a lower level, unless at a considerable distance from the sites of the wells.
These requirements are well fulfilled in the Libyan Desert, where the Nubian Series at the base of the Cretaceous consists of highly porous sandstones, subdivided by impervious beds of shale, overlain by a great thickness of absolutely water-tight beds, and underlain by probably almost equally impermeable crystalline rocks. These porous sandstones rise gradually to the south, and presumably outcrop in Nubia and the Sudan, though whether, as we shall see later, they derive their water-supplies from the Nubian reaches of the Nile, from the great swamp regions of the Sudan, or from the rains of Abyssinia or Darfur, is still, to some extent, an open question.
AN ARTESIAN WELL (BORE NO. 39).
In Northern Kharga we find two similar but distinct sandstones, separated by a 75-metre band of Impermeable Grey Shale. The upper bed, which we have for convenience designated the ‘Surface-water Sandstone,’ is exposed at the surface, and contains standing or sub-artesian water; while the lower, from which the flowing wells derive their supplies, never approaches within 80 metres of the surface, and forms the true ‘Artesian-water Sandstone.’ It will be convenient to give these sandstones separate consideration.
The Surface-Water Sandstone.
The stratigraphical position of the Surface-water Sandstone will be seen by reference to the geological sequence given in a preceding chapter, and to the section drawn across the oasis. The beds forming this division have an average thickness of 45 metres, and consist almost entirely of fine sandstones or coarser grits, often containing an abundance of oxide of iron, and occasionally beds of alum and Epsom salts, or, to be chemically exact, hydrous sulphates of alumina and magnesia. Thin bands of shale are frequently met with, intercalated in the sandstones, generally near the top or base of the series. On the level or gently undulating floor of the oasis, to the east of the line of disturbance passing through Jebel Têr, the Surface-water Sandstone has a wide outcrop, while to the west, where the general level of all the formations is higher, the same stage forms the foot-hills of Jebel Tarif, of Jebel Têr, and of the high cliffs which rise to the north of Um el Dabâdib and Ain Lebekha. It is probable, moreover, that the sandstones which form the surface of the desert between Kharga and Dakhla, and which cover immense areas to the south of the oases, also belong to this group.
Over a portion of the floor in the north of the depression these sandstones have been entirely removed by denudation, so that in this area the underlying grey shales form the desert surface. At one time the sandstone was continuous across the depression, and entirely covered by an impervious mantle consisting of the Purple Shales. It was then, in all probability, fully charged with water under pressure, as is the true Artesian-water Sandstone at the present day; and it is possible, as we have already suggested, that when the sandstones in question were first laid bare by the active agents of erosion, innumerable springs broke forth, and gave rise to a lake of considerable magnitude, which may, indeed, have been that which persisted into the historic period.
In the district round Headquarters several pits have been sunk in this sandstone, from which the water is lifted by power for purposes of irrigation. In six pits the maximum level of the water varies from 55·38 to 56·52, the average being 55·74 metres. From Headquarters the general surface of the country falls to the north, south, and east, and curiously the water-level in the sandstone falls in the same directions. In a pit near Bore No. 43, about 3½ kilometres to the south-west, the water-level is 52·4 metres; at points 640 metres and 2 kilometres to the west it was found to be 52·16 and 50·21 metres respectively; while near Bore No. 33, 4 kilometres to the north, the surface-water stands at 52·71 metres above sea-level. The ground-levels at these points are 54·54, 57·90, 53·61, and 57·61 respectively, while that at Headquarters averages 59·57 metres above sea-level.
For irrigation purposes an ordinary bore-hole or small pit is quite useless, the inflow of water through the pores of this sandstone being too slow to yield a pumping supply. When a large pit is excavated, fissures, through which water is seen to be freely circulating, are nearly always exposed. Experiments show that—provided a sufficiently large collecting-tank is made, measuring, for instance, 5 by 4 metres, and sunk from 1 to 2 metres below the standing water-level—a supply sufficient to yield a continuous discharge of 8 gallons a minute (equivalent to 11,500 gallons per day of twenty-four hours) can frequently be obtained. Moreover, by sinking a bore to a depth of 7 or 8 metres from the bottom of the pit, preferably on one of the fissures, the supply can be increased threefold, the water emerging from the bore in considerable volume, though with insufficient pressure to carry it (in a length of well-casing fixed on the top of the bore-hole) above the level of 55·74. The latter figure may, indeed, be regarded as the static head in this neighbourhood of the water in the Surface-water Sandstone. The fact that from this sandstone we are unable to obtain an artesian well at the surface, but can get flowing water at a depth of a few metres, is an important illustration of the very slight difference in some cases between flowing and non-flowing wells, and of their close connection with, and dependence on, the absolute ground-level.
The extent to which this sub-surface source can be drawn on without lowering its level has not yet been determined, though, in a pit alongside Bore No. 2, a ‘saqia’ or Persian waterwheel (a native contrivance adapted for lifting water, worked by oxen or camels), has been working for about eighteen months without appreciably affecting the supply.
We have seen that a flowing well can be obtained (in a pit) a few metres below ground-level, and under certain conditions it may be possible to obtain flowing wells at the surface from the sandstone under consideration; the occurrence of artesian water at El Dêr el Ghennîma, on the east side of the depression, may, indeed, be a case in point. To the east of Headquarters, as may be gathered from the section, the Surface-water Sandstone dips gently under the Purple Shales, the thickness of the latter increasing as the eastern escarpment is approached. Running north and south through El Dêr is an anticlinal fold, and flowing water is obtainable from wells sunk on its crest through the shales to the underlying sandstone. The original depths of the ancient wells in this district cannot be determined with certainty, but when one of those to the north of the ruined fort was cleaned out and cased, flowing water was obtained when the drill reached a depth of 41 metres. Below this the ground appeared to be untouched, the bore being carried a few metres deeper into fresh sandstone, which yielded an increased supply. This well has given a steady discharge of about 40 gallons a minute for over eighteen months. Quite recently the flow has been augmented to just over 50 gallons per minute by its outlet being lowered about 1½ metres, to 92½ metres above sea-level.
The water here seems to be derived from the Surface-water Sandstone, though, considering that the well is situated on a line of folding, it would not be advisable to entirely disregard the possibility of the presence of fissures, through which the water might rise directly from the Artesian-water Sandstone below. If, as appears to be the case from the depth and position of the bore, the water does have its origin in the Surface-water Sandstone, the explanation may be that the necessary working head or pressure is furnished by the difference of level of the sandstone here and in adjacent districts. In the extreme north of the oasis the same sandstone lies at a considerably higher level, and, at the same time, holds large volumes of water, and it may be that the pressure of this water, acting on that contained in the beds at lower levels, gives rise to flowing wells when bores are sunk in favourable localities.
A very great drawback to the water of these upper sandstones is its variable quality. In the Headquarters district it is usually more or less ferruginous, and in some pits may contain as much as 63 grains of dissolved solids per gallon, the salts consisting of iron, potash, and soda, with traces of lime and magnesia, mostly in the form of sulphates and chlorides. Mr. William Garsed[9] has calculated that this water would, if used for irrigation at the rate of 3 gallons a minute per acre, effect an annual deposition of over 3 tons of sulphate of potash and common salt on each acre of land. Salts of this nature in such quantities would, of course, have a very deleterious effect on the crops, not to mention the mechanical binding action of the iron on the soil.
It appears that the want of uniformity in the quality of the water is due to local causes, chief of which may be the relative abundance of fissures, the purity of the sandstone, and the presence or absence of mineralized shales. In those areas where the water is moving only slowly—where, in fact, it tends towards stagnation in the strata—it is probably liable to become more or less highly charged with mineral salts; certainly the best qualities seem to coincide with relative abundance, and the largest supplies are undoubtedly found where the beds are traversed by fissures.
In many parts of the oasis perfectly sweet water is obtainable from the sandstones of this series, and this source, as an auxiliary to the artesian supplies obtained from deep borings, was taken full advantage of in olden times. The ancients constructed the most marvellous systems of subterranean aqueducts to tap these sources, more especially in the neighbourhood of Um el Dabâdib, Qasr Lebekha, and Qasr Gyb, where such works were especially applicable, owing to the fact that the sandstones in those districts form extensive hills above the general level of the surrounding cultivable ground. These underground works are, in many respects, of far greater interest than the ancient monuments, and they will therefore be fully described in a later chapter.
The Artesian-Water Sandstone.
The source of the great majority of the flowing wells of the oasis is the group of sandstones underlying the Impermeable Grey Shales. Although the beds of the series are nowhere visible to the eye, their general characters can be judged by an examination of the material brought to the surface during drilling operations. The samples prove that, in general lithological characters, the Artesian-water Sandstones do not essentially differ from those just described. Throughout the area over which boring operations have recently been carried out no well-defined, continuous, argillaceous bands have been met with, though lenticular intercalations of clayey strata are not uncommon. Up to the present time the base of the Artesian-water Sandstone has not been reached, although the deepest borings have been carried down to a depth of 122 metres below its junction with the confining shales above. The different bands vary considerably in coarseness and porosity, in hardness, and in the amount of cementing material between the individual grains of the rock, all of which characters have a marked influence on their capacity as water-carriers. Judging from their unfossiliferous nature, from the presence of thin seams of lignite associated with bands and nodules of iron pyrites, and from certain other considerations, we are led to infer that these sandstones were originally laid down on the bed of an immense inland fresh-water lake.
During the past half-century the natives have put down a considerable number of deep bores in this and the neighbouring oasis. No written records concerning these are, however, available, so that in seeking information one has to rely on the memory of the men who sunk the wells. By careful cross-questioning I have collected a large amount of interesting and valuable information, but still, in describing the artesian wells themselves, it will be more satisfactory to confine our attention to those which have been drilled on the Headquarters area during the last two or three years, and of which accurate and reliable records have been preserved.
The Headquarters area, occupying the central part of the depression between Kharga village and Jebel el Ghennîma, is one of the few large districts entirely devoid of old wells and traces of former cultivation. A combination of unfavourable circumstances appears to have led the ancient well-borers to avoid this district. Firstly, the general elevation is comparatively high, meaning small flows from wells of ordinary depth; secondly, the superficial alluvial deposit is clayey and heavy, necessitating a considerable expenditure of time and labour to bring it into satisfactory condition for cultivation; and, thirdly, and probably most important of all, the presence of a copious supply of sub-surface water, which would have greatly hampered, if not made impossible, the sinking of wells by the ancient system.
It may therefore be assumed that, owing to the entire absence of both ancient and modern wells, the sandstones of this district were practically fully charged with water at the time the first bore was sunk.
The junction of the Artesian-water Sandstone with the grey shales above is usually fairly abrupt, the first flowing water being obtained as soon as the drill strikes the top of the sandstone. Where alternating sandstones and shales occur at or near the junction, the former are generally charged with water under feeble pressure, yielding flows at the surface of from 1 to 5 gallons a minute. Sometimes, indeed, the piercing of these thin bands, prior to the main body of sandstone being entered, merely results in a rise of water in the bore-hole, without actual flow. On drilling into the sandstone proper, increments of the flow are obtained at fairly frequent, though irregular, intervals of depth. At times the discharge is seen to increase slowly but steadily, while a particularly porous bed is being passed through; at others the rate of increase is so rapid as to suggest that a fissure charged with freely flowing water has been struck. As a rule, hard beds of sandstone, (the ‘shells’ of American drillers) overlie the best water-carrying layers, and though these act locally as confining beds, there almost certainly is, nevertheless, an intimate connection between different parts of the sandstone, as no persistent argillaceous bands have been met with.
Loose uncemented sands may be encountered at any time, but do not seem to coincide with marked increases of flow. These ‘quicksands’ form one of the greatest difficulties with which drillers have to contend, and many bores have perforce to be discontinued owing to the impossibility of drilling through them. The loose sands ‘cave’—that is, run in from all sides—the whole wall of the bore at times falling in, throughout a length of 5 or 10 metres. The only remedy against caving is the insertion of casing, but this is generally undesirable, as it may effect the shutting off of water already obtained from the upper bands of the sandstone; in some cases, however, perforated lining may be satisfactorily employed.
Of thirty-one bores finished in this district, none has failed to strike water, though three have yielded such small flows that they may be regarded as comparative failures. The average flow of the thirty-one wells, the measurements being made in each case a week or two after completion, was approximately 100 gallons a minute, the maximum being 315 and the minimum 18 gallons per minute. All bores have shown a marked decline in discharge for some time after completion, when, if isolated, they have settled down to a fairly steady flow, or at least to a flow which decreases at a constantly diminishing rate.
Owing to the very adverse effect of some of the larger bores (situated on the lower parts of the area) their flows have been purposely reduced; and as a further precaution against over-exploitation, and as a remedy to the waste consequent on irrigation at night, all wells are, as far as possible, shut down between sunset and sunrise. The average discharge, therefore, at the present day is considerably less than the figure mentioned above, amounting, in fact, to approximately 70 gallons a minute per bore.
By far the most important factor determining the volume of flow is the absolute ground-level at the mouth of the well. The floor of the oasis in the district in question lies between 53 and 61 metres above sea-level, the general slope being to the west, in the opposite direction to the dip of the water-bearing sandstones. Although the actual difference of level is so little, amounting only to 7 or 8 metres, the difference of flows from wells of equal depth on either side of the area averages fully 100 per cent. This indicates that the surface of this area is very near the static head or limit to which water will rise from bores of this depth; in fact, if the ground were raised by a very few metres, not one of the wells would discharge at the surface. This I have proved by actual experiment, and it is, moreover, borne out by the observed pressure, which even in the best wells seldom amounts to more than 13 or 14 pounds to the square inch.
Before going further into this important matter of pressure, let us briefly notice the temperature and chemical composition of the artesian water. In Dakhla Oasis the temperature of the wells often rises as high as 90° or 95° F., the highest recorded being 105° F. in Bir el Dinaria, a bore sunk fifteen or sixteen years ago, and the deepest and most northerly in that oasis. In Kharga it is seldom that we meet with temperatures over 90° F., the well-waters at Headquarters varying from 86° to 88° F. Identical figures were obtained in the southern part of the oasis.
One of the most noticeable features of the artesian water is its highly effervescent character when it reaches the surface. In most of the newer bores the water is so strongly charged with minute bubbles of gas that it closely resembles the contents of a newly-opened bottle of highly aerated water, while in many of the older wells the gas rises to the surface in a slow procession of large bubbles.
Analysis shows the gas to consist almost entirely of nitrogen, only small quantities of oxygen and carbon dioxide being present; and it has been estimated by rough experiment that the volume of gas issuing from Bore No. 1 (internal diameter, 4¼ inches) amounts to half a pint per minute. My own opinion is that this nitrogen represents ordinary air deprived of its oxygen during the underground passage of the water, and this explanation seems confirmed by Mr. Lucas, F.C.S., Chemist to the Egyptian Survey Department, who refers me to several cases in which air is believed to have been depleted of its oxygen by pyrites, etc., during its passage underground.
The quality of the artesian water is in all respects excellent, and when taken direct from a cased well forms, after cooling, a palatable water free from all danger of contamination. Analyses by Mr. Garsed of water samples from four bores show the total dissolved solids to range from 43 to 47 parts per 100,000, equivalent to from 30 to 33 grains per gallon. In new bores the water is usually only slightly ferruginous, though, as already mentioned, in some of the ancient wells of certain districts it is so highly charged with ferric oxide that thick deposits of ochre have been formed along the irrigation channels.
The chemical composition of the dissolved salts, so far as determined, is shown in the following table:
ANALYSES OF TYPICAL ARTESIAN WATER OF KHARGA OASIS (HEADQUARTERS DISTRICT).
| Bore No. 1. | Bore No. 2. | Bore No. 5. | Bore No. 6. | |
|---|---|---|---|---|
| Total solids (grains per gallon) | 33 | 30 | 33 | 32 |
| Composition of dissolved salts, per cent. | ||||
| Silica | 4·2 | 4·5 | 4·6 | 3·4 |
| Ferric oxide | 1·7 | 0·8 | 1·2 | 1·3 |
| Lime | 6·5 | 7·0 | 5·4 | 5·6 |
| Magnesia | 2·9 | 3·1 | 2·7 | 3·8 |
| Sulphuric anhydride | 4·5 | 4·9 | 4·4 | 4·4 |
CHAPTER X
FLOWING WELLS: SOME
EXPERIMENTS AND OBSERVATIONS
Total Water Discharge of Oasis — Water-Pressures — Static Head — Importance of Systematic Observations and Records of Bores — Sensitiveness of Wells — Experiments showing Mutual Interference of Wells — Bores Nos. 5 and 6 — Bores Nos. 4 and 42 — The Wells at El Dêr el Ghennîma — Decline in Discharge of New Wells — Effect of Closing Bores — Rate of Flow of Water in Sandstones — Danger of Over-Exploitation — Holding Capacity and Porosity — Experiments on Porosity of Nubian Sandstone — Large Quantities of Water held in Storage Beds — Economically only partially available at Surface.
At the present day there are about 230 native-owned wells in the oasis, yielding a total discharge of some 295 qirats. We have seen that the qirat has not a fixed value, but represents a discharge varying from 22 to 38 or more gallons a minute. Applying these values as far as possible to the old wells, and adding the known discharge of the new, we shall not be very far from the truth if we estimate the total discharge of the oasis wells at 8,000 gallons a minute, or 11,500,000 gallons (53,000 cubic metres) a day. The largest well in Kharga Oasis is Ain Estakherab at Gennâh, with a discharge of between 700 and 800 gallons per minute. The average yield of those which might be described as the best wells probably does not exceed 150 to 200 gallons, while there are a great many which only discharge 20 or 30 gallons per minute.
In some parts of the world the discharges of artesian wells are measured by thousands, not hundreds, of gallons. In Queensland and other parts of Australia, for instance, there are numerous bores throwing over 1,000 gallons a minute; in these regions the depth of individual bores in many cases amounts to thousands of feet, the pressure frequently rising as high as 100 pounds to the square inch. It must, moreover, be borne in mind that the artesian basins of Australia have only been exploited during a comparatively short period, and that from the nature of the country the wells are, as a rule, at considerable distances apart.
The exploitation of the artesian basin of the Libyan Desert has been in progress for hundreds and thousands of years, and it is probable, therefore, that in the oases-depressions the general average pressure has been very much reduced. At the present time the water-pressures seldom exceed a very few pounds per square inch, so that the static head, or absolute height to which the water will rise, is seldom more than a few metres above the actual surface of the ground. The outlets of the native wells are, unfortunately, of such a nature that it is not possible to make even approximate determinations of pressure; but after taking into account the influence of ground-level on the volume of flow, we still find differences which point to there being considerable variation in the absolute static head in different parts of the oasis—that is to say, the water will rise higher in some places than in others. This is probably partly to be accounted for by variations in the level of the underlying strata and by the presence of faults—for instance, the static head to the west of the central line of disturbance is certainly considerably higher than to the east.
In the absence of accurate data, the static head in a district can be approximately gauged from the ground-level and flow of any one of the higher and more isolated wells. The maximum static head judged in this way appears to be 88 metres above sea-level in the Kharga district on the west side of the fault; but in the Headquarters area, to the east of the fault, it can be definitely proved to be very much less.
In order to determine the extent of the local variations throughout the district where the recent boring operations have extended, I carried out a number of experiments. For this purpose four bores in different parts of the area were selected, of similar diameters, and of approximately equal depths into the water-sandstone. By means of a flange the casing of each bore was carried vertically upwards, the ordinary outlet being kept shut until the pressure ceased to rise, as indicated by a pressure-gauge. It was then found that in Bore No. 36 the water had risen to 61·6 metres, in Bore No. 38 to 59·55, in Bore No. 42 to 64·26, and in Bore No. 44 to 62·0 metres above sea-level. The average static head in this district may therefore be taken as 61·85 metres. The positions of the four bores in question, with regard to Headquarters, are as follows: No. 36, 7·7 kilometres N.; No. 38, 2·6 kilometres N.W.; No. 42, 1·6 kilometres S.E.; and No. 44, 3·9 kilometres W.N.W.
To the north of Meheriq the static head appears to rise, as flowing wells are found up to 76 metres above sea-level (Ain Mohammed Delaib). The water-level at Ain el Ghazâl is even higher (84·56), but this well does not actually run.
In the development of an artesian basin this question is of the utmost importance; only by a knowledge of the static head and the ground-level can we, with any likelihood of success, estimate beforehand the discharge to be looked for in any particular district. If, for instance, we sink a bore in a locality whose surface is above the static head, the result, so far as a flowing well is concerned, can only be failure, however great the amount of water existing in the underlying strata. If a sufficient number of observations are available, it is possible to construct charts showing the isopotential lines, or lines of equal pressure, and these may be of great value when boring is contemplated in intermediate districts.
It is seldom that accurate records of bores are preserved in the initial stages of the development of new artesian basins, and to this neglect is due much of the doubt which frequently arises at a later period as to the extent and permanence of the underground water-supplies.