Schweinfurth’s report on the probable salt-content in Wadi Rayan Reservoir.In an appendix[23] to the above report Schweinfurth discusses the question as to how salt the water of such a reservoir would become. He points out that the exact valuation of the salt which would be contained in this reservoir when the water had risen to + 27 metres cannot be accurately determined, owing to the absence of information on certain points. The maximum quantity of salt in the desert soil is estimated at 2% and this figure is used in his calculation, which includes the amount of salt which would be brought into the reservoir, (1) from the Nile during filling and in the extra water entering to replace that lost by evaporation in the lake and canals; (2) from the ground forming the bed of the lake (far the largest item); (3) from the bed and banks of the inlet canal, both in the desert and in the Nile Valley; and (4) from infiltration. The figure obtained is 7,500 million kilogrammes, equal to 0·04 per cent, or almost one twenty-fifth per cent of salt. This amount is only equivalent to half the salt existing in many of the well waters used in the country for irrigation. As Schweinfurth is careful to point out his calculation is based on maximum and assumed data.

Willcocks’ “Assouan Reservoir and Lake Mœris”.The question of the utilisation of the Wadi Rayan as a reservoir has recently been again brought to the front, notably by Sir William Willcocks in a paper[24] read before the Khedivial Geographical Society, Cairo. The author, after pointing out the value of such a lake, working in connection with the Assuan reservoir, discusses at length the position, dimensions, and functions of the ancient Lake Moeris. It is suggested that the main canal should be cut through the desert opposite Mazana and crossing the so-called wadis Liernur and Masaigega enter the Wadi Rayan at its easternmost point. These wadis would in time become covered with alluvium and be converted into valuable cultivated land. After examining the big ravines of the Fayûm, where similar beds are exposed, the author comes to the conclusion that the maintenance of canals in the saliferous marls, which form part of the desert through which the inlet canal would pass, would offer no particular difficulties.

With regard to the questions of leakage into the Fayûm and of the water of the lake eventually becoming salted, Sir William Willcocks says, “When the old Lake Moeris, or the present Fayûm, was full of water and 63 metres higher than the bottom of the Wadi Rayan and remained so for thousands of years, there was no question of the waters having become salted or having escaped into the Wadi. The Wadi was as dry as it is to-day and the great inland sea was always fresh.” As to the question of leakage into Gharaq the author considers that if water found its way into that depression it would be a distinct advantage, as such water could be pumped into the Nezleh canal and utilized elsewhere; he maintains at the same time that no leakage will take place. Incidentally it is mentioned that the Wadi Rayan is separated from the Fayûm by a limestone ridge, a statement which, as will be shown later, requires modification.

Wadi Rayan not yet examined in detail by the Geological Survey of Egypt.Until a detailed geological examination of the Wadi Rayan and neighbourhood has been carried out it will not be possible to form reliable opinions on many of the questions raised in connection with the prospective reservoir. The writer’s acquaintance with the area is limited to a traverse in 1899 from the Nile Valley through Wadi Muêla to Rayan and thence to Gharaq, and subsequently to a stay of a few days duration in the neighbourhood of the Rayan springs, after mapping the extreme south-west of the Fayûm depression. While the accompanying maps may be taken as representing fairly accurately the bolder topography of the region, they do not replace the older contoured maps of the floor of the depression and the country between it and the Nile Valley to the east, accompanying the report on “Perennial Irrigation and Flood Protection in Egypt.”

The following description of this part of the district is based on a traverse from the Nile Valley through the wadis Muêla and Rayan to Gharaq; the detailed geological sections measured and examined along the line of route will be given later.

Traverse from Nile Valley through Wadi Muêla to Rayan and Gharaq.Between the village of El Gayat and the mouth of the Wadi Muêla (16 kilometres to the north-west) stretches a gradually rising undulating gypseous plain, superficially covered with loose sand and rounded pebbles of quartz and flint. In occasional small hills the white limestone which forms the underlying rock is visible. Near the entrance to the wadi stands a somewhat prominent conical hill composed of hard whitish fossiliferous limestone passing down into more sandy and clayey beds. The bottom of the wadi is cut out in soft green and brown clays, its surface being covered with blown sand, fragments of limestone, flints and gypsum. From the mouth of the wadi the Nile Valley cliffs run north and south in a winding irregular manner. On entering the valley several outstanding flat-topped limestone capped hills are passed on the right hand; they are in part joined to the regular bounding cliff beyond; the eastern cliff is steep and well-marked, while that on the west only outcrops here and there, buried as it is in immense accumulations of blown sand, rising in places into definite dune-ridges. Wadi Muêla has a length of some 18 kilometres and lies nearly N.W. and S.E. The central part of its floor is a sandy scrub-covered area, the lowest points lying at about + 25 metres; just at the southern edge of the scrub stands a small hill composed of hard shaly clays capped by white limestone, surrounded by a saline, superficially dry. Holes dug in this are at once filled with excessively salt water, and by evaporation of the brine in shallow troughs supplies of white fairly pure salt can be obtained. The area is known as Warshat el Melh in Wadi Muêla.Warshat el Melh. Banks of reeds were found growing on the north side of the saline, the surface of the latter being here composed of a soft brown sandy salty deposit, caking here and there into a hard earthy impure salt.

In the lowest spots the saline frequently consists of soft wet sludge; its area is about half a square kilometre but the depth of the deposit is unknown. In the middle of the scrub-covered area to the north lies Ain Warshat el Melh, a pool of water, fairly fresh and drinkable, although ferruginous, measuring 10 by 5 metres in size and from 2 to 2½ metres deep. The water evidently rises from a spring on the west side, round which are fifty square metres of green rushes, with some larger bushes. The ground around and above is very saliferous; between the spring and the ruins to the north the ground is sandy, with many bushes and much scrub. This ground extends two kilometres to the west, whence it gradually passes up into great masses of drift sand; an occasional small outcrop of the top of the plateau above the sand is all that serves to locate the position of the buried cliff. On the east side the sandy ground with scrub extends about a kilometre, beyond which the plain gradually rises for another kilometre to the base of the cliff beyond, which is fairly steep and well-marked, though with an entire absence of indentations of any kind.

Der el Galamûn.Close to the north end of the valley, and about 33 kilometres from El Gayat, lie the ruins known as Der el Galamûn bil Muêla. At the time of our visit a new square stone building was in course of erection and five or six persons were inhabiting the place. There are several small palms scattered about to the south of the monastery and an excellent running spring of clear water five hundred paces to the south-west. A new well is being sunk within the premises. To the north of the monastery the eastern cliff takes a marked trend to the west for some three kilometres, whence it resumes a northerly direction, always maintaining its character of a steep well-marked escarpment rising some 100 metres above the floor of the wadi. At the corner of the cliffs the lowest bed exposed is a white limestone; this is overlain by gypseous clays passing up into sandy beds, the latter being surmounted by the white limestone capping the escarpment.

Wadi Rayan.We are here on the summit of the divide between Wadi Muêla and Wadi Rayan, the height of the floor being about + 105 metres; to the north stretches a gradually widening bay descending to the lowest ground of the Rayan depression. Immense accumulations of sand almost block the defile and stretch away to the east, and the hitherto well-marked cliff on that side bends back and is lost to view. On the other side however, the bounding wall gradually emerges from the dunes, getting more distinct as it is followed northwards until it becomes quite clear of the sand. The first glimpse of this cliff is seen a couple of kilometres west of the pass in an outcropping headland, the next point visible being some five kilometres further west. Between these portions of the cliff are one or two outliers, surrounded by quantities of blown sand. A depression known as Wadi Korif is reported to lie to the west, and much scrub and some water is said to exist there; such a wadi is marked on Schweinfurth’s map but apparently has not been examined.

Continuing in a N.N.W. direction high rather steep dunes occur on either flank, running N.N.W. and S.S.E. Between the dunes is a fairly hard undulating sand-flat affording an easy route; further on a narrow defile between the dunes leads down to the centre of the depression. The main areas occupied by blown sand are shown in the accompanying maps. The most interesting part of the depression is the bay lying to the south of the narrow well-marked promontory jutting out from the southern plateau, a huge pointer, as it were, in the direction of Gharaq; this is the Cape Rayan of Schweinfurth.

Springs in Wadi Rayan.The bay is on three sides completely enclosed by cliffs and its floor is thickly covered by a luxurious growth of wild scrub—chiefly tamarisk and ghardag; numerous isolated palm trees occur, especially in the neighbourhood of the water which exists at several points. There are three particularly good springs,[25] the positions of which are shown on the accompanying maps. According to Colonel Western’s survey the water emerges at about + 20 metres. In 1899 the water of the northern spring was found to have a temperature of 26°C. On our last visit we found an artificially constructed pool of two metres diameter and a depth of 30 centimetres; on the west side of this were two springs, marked by the motion of the grey sand rising and falling in the vents, down which a stick could be easily pushed to a depth of two metres. The output of these springs together amounted to six litres a minute; the water was quite clear and although soft and rather ferruginous not by any means unpalatable (see analyses below). The pool lies on an open bare sandy spot and is surrounded by scattered bushes, none of which however are within fifteen metres; a sand dune lies 150 metres to the south-west, with bushes and seven or eight young palms. The southerly spring has an output of 21 litres a minute, and its water does not differ essentially from that of the northern spring. Rising at the foot of a palm tree it forms pools on either side; thence it flows a distance of 20 metres into an artificially constructed shallow basin 2 to 3 metres across, from which it runs away down the slope and disappears after five or six metres. The east spring, which is situated on the east side of the dunes bounding the mouth of the bay, consists of a small hole cut out in soft sand. The water seemed good, although analysis shows the salts content to be high; this spring does not run, but if emptied the hole soon refills. The remains of old buildings occur near the well, in the shape of loose roughly squared limestone blocks, broken pottery, and remains of old walls; the latter are nearly level with the ground and very thickly and solidly built.

To the south of the promontory lies the so-called Little Rayan. Here there is a good deal of scrub, and water can be obtained on the lowest ground at a few metres depth, although there do not appear to be any surface springs.

Geology of Wadi Rayan in broad outline.The geological succession of beds exposed in the cliffs of the promontory is given later. Broadly speaking it consists of two thirty-metre bands of hard limestone separated by 68 metres of softer sandy and clayey beds. The lower of the limestone bands in places forms the floor of the depression but more frequently the latter is composed of the overlying sandy or clayey beds. The depression is bounded on the north side by the same succession, and, as far as could be judged from observations made on the traverse, the bed of limestone capping the ridge, and forming the plain stretching away to the Birket el Qurûn and to Gar el Gehannem, is identical with that capping the cliffs to the south, i.e. is the uppermost of the two thick limestone bands. At the two points more particularly noticed, namely, the spurs projecting southwards into the depression, 23 kilometres west and 18 kilometres W.S.W. of Gharaq basin, the sequence seemed to be the same as in the southern cliffs, although, owing to the northerly dip, the upper bed of limestone lies at a much lower level and the basal beds are not exposed at all. In both these localities, however, some of the underlying clays were exposed, as well as on the lowest spots crossed between the most easterly spur (18 kilom. W.S.W. of Gharaq) and the extensive dunes lying immediately west of Gharaq cultivation. These dunes, though of no height, have remarkably steep sides. In crossing Gharaq to the Fayûm cultivation occasional beds of yellow sandy limestone were noticed, but their horizon was not determined. Numerous bored blocks, probably belonging to the marine Pliocene, were observed scattered about. Apparently the uppermost thirty-metre band of limestone passes continuously northwards under the cultivated lands of Gharaq and the Fayûm; in the ravines of the latter this limestone is not observed, the soft limestones exposed below the alluvial deposits almost certainly belonging to the overlying Ravine beds. The country to the east of Gharaq has not been geologically examined and the exact locality in which the thick bed of limestone dips underground and is overlain by the succeeding beds is doubtful. Further north, in the desert ridge east of Qalamsha, we have observed the Birket el Qurûn beds and a section measured at this point is given later.

Character of Ridge separating Wadi Rayan from Gharaq and the Fayûm.As it appears to have been freely assumed that the ridge separating the Rayan depression from the cultivated lands of Gharaq and the Fayûm is formed throughout of solid limestone, it is important to point out that, on our assumption of the identity of the beds of limestone capping the cliffs to the south and the plain to the north of the Wadi Rayan, the dividing ridge would in part be formed of the underlying arenaceous and argillaceous beds.

Question of leakage through dividing ridge.The absence of Nile deposit and freshwater shells in the Wadi Rayan will, when confirmed after a thorough examination of the area, afford the strongest evidence that the depression was never directly flooded by Nile water. The fact that the dividing ridge is probably everywhere above the highest level attained by Lake Mœris, and by the still more ancient prehistoric lake, is almost sufficient in itself as a proof of this. It does not however follow that there was not leakage through the ridge into the Rayan basin, as such leakage might conceivably have taken place to a considerable extent without the water ever having collected in sufficient quantities to form even moderate sized pools within the depression. The bottom of the depression is for the most part covered with soft porous sandy deposits overlying the Eocene bed-rock below, and at the present time the water of the Rayan springs, though continually running, at once disappears from sight, drains down to the lowest parts of the depression and is then gradually lost by evaporation or underground leakage. In the lowest parts of the depression this water is, as already mentioned, met with on digging to a very moderate depth.

A careful examination of the flanks of the ridge separating the Fayûm and Gharaq cultivated areas from Rayan might prove if such leakage ever took place. If such was the case the seepage was probably along the line of junction of the limestone and underlying clayey or sandy beds. Even if it were proved that there never was leakage from Lake Mœris into Wadi Rayan, it would not be safe to assume that the converse would not happen, as the dip of the beds is from south to north and this fact is one to be reckoned with. Judging from the nature of the Eocene beds forming the Wadi Rayan, my opinion is that leakage on a large scale would not take place, and that owing to the northerly dip any water that escaped from the reservoir would pass indefinitely northwards and would not find its way through the overlying limestone to the surface either in Gharaq or the Fayûm cultivation. A detailed examination of the local geology would, however, be necessary to prove or disprove this. As to the question whether the Wadi Rayan as a whole would hold water, as far as is known there are no faults or other fissures of any magnitude through which the water could escape. No doubt a good deal of water would be lost before the smaller joints and passages, which exist in all rocks, were silted up. Schweinfurth supposes that the freshness of the Birket el Qurûn is due to the existence of subterranean outlets, and such might also be found to exist in the Wadi Rayan. In any case the argillaceous deposits from such a lake would very soon form a bed to all intents and purposes impermeable.

Degree of Salinity.With regard to the extent of salinity of such a lake Dr. Schweinfurth’s figures are of considerable interest and value, although based wholly on assumed data. The greater part of the salt would be derived from the rocks and soil forming the bed of the reservoir and only by extensive sample collecting and analysis can reliable figures be obtained. We believe that in the lowest parts of the basin the salt content of the ground would be found considerably in excess of the two per cent used by Schweinfurth in his calculation, although his total estimate would probably be found well within the mark.

Section V.—CENTRAL AREA OF THE REGION.

Central Plain at the Fayûm Depression.The great central plain, forming the floor of the depression as a whole, is composed of a hard bed of limestone some thirty metres thick. This limestone, forming the uppermost member of the Rayan series, is, as already mentioned, almost certainly identical with that capping the cliffs to the south of the depression, and in all probability in the eastern extension of the plain under description underlies the whole of the cultivated lands of Gharaq and the Fayûm. The feature of the plain as a whole is its marked and constant, though low, dip to the north; so that its surface, bared by denudation of the overlying soft limestones of the Ravine series, over a distance of some twenty kilometres, is a true dip-slope, at the base of which lies a strip of low-lying country extending from beyond Gar el Gehannem through the Birket el Qurûn to the Nile Valley ridge east of Tamia. The central and lowest portion of this low-lying area is occupied by the Birket el Qurûn, the bed of which lies fifty metres below sea level and is thus the lowest known spot in the whole of the Libyan desert. Thirty kilometres south-west of the western end of the lake, at the base of the dip-slope of the central plain and immediately under the southern scarps of the great outlying hill-mass west of Gar el Gehannem, lies another low lying basin, which receives the drainage from a considerable area of the plain to the south-west. The latter, consisting of the limestone above-mentioned, is here superficially covered by gravel, and its dark undulating surface is scored by numerous shallow winding water-courses marked by an abundant growth of scrubby vegetation; some of the principal of these drain into the basin just mentioned and after heavy rainfall the water collects and forms a pool 600 metres in length by 100 to 150 metres wide. The base of the basin, at about 80 metres above sea level, is marked by a level deposit of silt of considerable thickness, the east end of the site being surrounded by great numbers of luxuriantly growing tamarisks. Other similar basins exist on the plain to the south, and under an isolated hill five kilometres W.S.W. several full grown acacias were noticed. On the low ground to the north-west of Gar el Gehannem, and at several points between it and the head of the Birket el Qurûn, similar silt covered areas exist, some being only from 30 to 40 metres above sea level.

In the extreme south-west of the region the limestone forming the central plain is gradually overlain by the succeeding beds, so that the ground rises imperceptibly to the level of the plateau separating the depression from that of Baharia, distant some two days march. On the eastern side, if the superficial alluvial deposits could be stripped off, the underlying surface of limestone, sloping from south to north, would not differ materially from the plain further west, except that here, at any rate north of Gharaq, the Rayan limestone is overlain by the basal beds of the Ravine series.

Section VI.—RIDGE SEPARATING THE NILE VALLEY AND THE FAYUM.

The desert ridge separating the Nile Valley from the Fayûm has, to the north of the Bahr Yusef, an average width of some ten kilometres; further south it narrows, until due east of Gharaq the ridge is barely 2½ kilometres wide. The highest points are situated to the east of Sersena and Qalamsha respectively.

In both these localities the Eocene rocks, consisting of clays alternating with beds of calcareous sandstone and sandy limestone (pp. 39, 40) are overlain by thick deposits of conglomerate and gravel, attaining altitudes of over 100 metres above the cultivated land below. From these summits the slope is usually very gradual on the Nile Valley side but much more rapid towards the Fayûm.

The ridge is cut down, however, to a comparatively low level in four localities; to the north-east of Tamia; to the east of Sêla, where the railway crosses; between Lahûn and Hawara, where the Bahr Yusef canal enters; and to the south of Qalamsha, where along the site of the proposed Wadi Rayan canal the highest point is only some 40 metres above the Gharaq basin and 27 metres above the adjoining Nile Valley cultivation.

Outline of earliest connection of Nile with Fayûm.One of the most interesting problems connected with the Fayûm may be briefly alluded to here—When did the waters of the Nile first obtain access to the depression?

As will be shown later the Fayûm was occupied by the sea in Pliocene times, when the great gravel accumulations and gypseous deposits were formed. Later the area became dry and denudation of the land surface completed the work of erosion already begun in earlier times.

In Pleistocene times drainage down the Nile Valley appears to have become definitely established and probably the river in the lower part of its course eventually washed up against and broke down the separating barrier of gravel between the Fayûm and the Nile Valley, so that part of its waters obtained access to the depression, formed a lake on the lowest part, and gradually rose until the whole basin, up to the level of the channel connecting it with the Nile Valley, became filled. Every year thousands of tons of sediment were carried in by the floods and spread out on the floor in the shape of a fan. Probably later, as the Nile level fell, the valley and the depression again became disconnected, until the more modern river, with its gradually rising bed, again attained the requisite altitude. In early historic times the alluvial deposits had probably silted up the lake in its southern central part, and when in the XIIth dynasty the district was first taken in hand by Amenemhat I this part of it must have had the character of a huge marsh, nearly surrounded by open water, rapidly deepening towards the north.

Section VII.—THE NORTHERN DESERT REGION.

The Plateau bounding the Fayûm depression to the north.All along the north-west and north sides the ground rises rapidly from the base of the dip-slope of the plain in a series of escarpments to the summit of the rim of the depression, averaging 340 metres above sea level. Northwards from the summit stretches a rolling pebbly desert, the prevailing character of which is a dark brown, relieved by lighter brown grey and yellow patches, and especially flecked by the light sandy slopes of the undulations. Although the latter seldom rise to any considerable height above the general level of the plain, from the top of the most modest eminence an immense view in every direction can frequently be obtained. The monotony of this desert is only relieved by the occasional belts of sand, which although extremely narrow in width, run for immense distances in almost absolutely straight lines, and in a N.N.W.—S.S.E. direction. Although none of these dunes actually reach the rim of the escarpment we may mention here the beautiful Ghart el Khanashat, an almost straight and apparently unbroken ridge of sand, extremely narrow but of great length. Near its southern extremity the width does not exceed 100 metres; the slopes on both sides are frequently as much as 30°. The commencement of the Ghart el Khanashat was observed on a march from Wadi Natrûn to Mogara; it lay some way to the south of a line joining those two localities but could not be accurately fixed from the line of route. The belt dies out 24 kilometres from the rim of the Fayûm depression, its termination being particularly abrupt, although the height of the ridge diminishes gradually throughout the last kilometre or two. The line of the belt if continued would almost strike the western extremity of the Birket el Qurûn; near its termination the desert is almost flat, the surface being finely gravelly, with numerous groups of silicified trees; tufts of coarse grass grow in some profusion on the sandy ground at the base of the ridge on either side. A fairly well-marked road from the Birket el Qurûn to the Wadi Natrûn passes the end of the ridge and continues northwards at a distance of 200 metres from the east side of the dunes, although apparently gradually diverging eastwards.

Except to the north and north-west of Tamia, where a somewhat extensive and fairly level plain exists, the ground, as already mentioned, rises from the limits of the central plain in a series of escarpments to the summit of the rim of the depression. These cliff lines are broadly speaking three in number and represent the escarpments of the three great rock-stages which build up the northern part of the Fayûm, i.e., the Birket el Qurûn series, the Qasr el Sagha series, and the Fluvio-marine series. It would serve no useful purpose describing these different cliffs in detail; their positions and characters are apparent on the accompanying maps. The intervening plateaux are for the most part dip-slope plains formed of hard bands of rock, which resisting denudation, are left protecting the underlying strata while the softer beds above are cut back at a comparatively rapid rate.

Desert west and south-west of Gar el Gehannem.In December 1902 and March 1903 a traverse was made through the unexplored country west and south-west of Gar el Gehannem, finally connecting up with Wadi Rayan. The highest escarpment, i.e. that of the Fluvio-marine series, dies out about 20 kilometres west of Gar el Gehannem, gradually merging into the undulating gravel-covered plain. The lower escarpments, those of the Qasr el Sagha and Birket el Qurûn series, continue to a considerable distance in a south-westerly direction, although gradually losing the characters of well-marked cliffs. In fact westwards of this the depression gradually shallows, until at a point some 50 kilometres south-west of Gar el Gehannem the floor has attained the level of the ordinary desert plateau, on which the outcrops of the beds of successive rock-stages follow one another in regular order from south to north, but without forming well-marked topographical features, as in the depression.

Hills, capped with dark hard ferruginous silicified grits and puddingstone, were met with in the extreme south-west extension of the depression; these deposits, which will be referred to more fully later, considered in conjunction with the similar beds occurring within the oasis of Baharia, and in the hills of Gar el Hamra, on the plateau immediately to the north-east of that depression, are of considerable interest and importance, especially in connection with the question of the position of the early rivers which in Eocene and later times brought down quantities of trees and animals, the remains of which are so abundant throughout the later Fayûm deposits.

Jebel el Qatrani and escarpments north of the Birket el Qurûn.The boldest part of the region is the area lying between the Birket el Qurûn and the summit of the depression to the north. All three lines of cliff are here high and precipitous, and the uppermost escarpment, well known by the name of Jebel el Qatrani, formed of a highly coloured series of sandstones and clays and capped for a distance of many kilometres by a thick bed of hard black basalt, is of a most striking character. The eastern extremity of Jebel el Qatrani is perhaps the most conspicuous point in the whole region; here the two conical black basalt-capped cliff-outliers, known as Widan el Faras, stand side by side, and from their summits the eye commands the whole region from the pyramid of Lahûn on the one side, across Rayan to the south, up to the extreme limits of the depression to the south-west. The rim of Jebel el Qatrani has a fairly constant level of about 340 metres above the sea. From Widan el Faras the escarpment trends northwards for a few kilometres before again resuming an easterly direction, which is continued till the well-marked bluff of Elwat Hialla is reached. From this summit the pyramids of Dashûr, Saqâra and Giza are visible to the north, as well as Cairo and the Nile Valley southwards, backed by the bluffs on the Eastern desert limestone plateau.

To the south the isolated peaks of Garat el Gindi and Garat el Faras form conspicuous landmarks on the more or less open plain which stretches to Tamia and the limits of the Fayûm cultivated lands. Eastwards the escarpments continue in a broken irregular manner; the upper ones are gradually lost in an undulating plain, while the lower eventually join those forming the northern part of the ridge separating the Fayûm from the Nile Valley.

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PART II.

TECTONICS.

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Section VIII.—FAULTING AND FOLDING.

The Fayûm Depression formed by subaerial Erosion.More extended examination of the Fayûm region supports my original conclusion[26] that the depression owes its origin to the same causes as have given rise to the other oases-depressions of the Libyan Desert, namely Baharia, Farafra, Dakhla and Kharga[27]. No evidence has as yet been met with which would suggest that earth-movements have played any important part in the formation of the Fayûm depression. Local faults, for the most part of short length and slight throw, occur at certain points, but the influence of these is strictly limited to their immediate neighbourhood. In fact, an examination of the desert margin of the Fayûm conclusively proves that the depression has been cut out through the action of ordinary subaerial denuding agents. The somewhat prevalent idea that the central portion of the depression, that covered by alluvial soil and the water of the lake, is faulted down, also rests on no foundation, all available evidence pointing in an opposite direction. Throughout the margin of the alluvial covered area the Eocene beds forming the surface of the desert can be observed to pass regularly under the cultivated lands; moreover, the same strata are frequently exposed in the bottoms of canals, drains, etc., far within the cultivation. The big drainage ravines of El Bats and El Wadi are, through a large part of their courses, cut down to the underlying Eocene rocks (Ravine beds), and in every locality examined the strata were found in the position they would be expected to occupy if undisturbed by tectonic movements.

Deep boring at Medinet el Fayûm.The evidence yielded by the deep boring at Medinet el Fayûm is, as far as it goes, to the same effect. The ground level at the site was at 23·40 metres above sea-level and the following beds were passed through[28]:—

			Metres.
Alluvial clays, clayey sands and sands, the latter in part coarse and pebbly			18·5
Yellow, brown, and grey marls and marly clays (probably belonging for the most part to the Ravine beds)			112·5
Cement coloured stone	⎫ ⎪ ⎬ ⎪ ⎭	Probably these limestones and occasional marls and clays belong to the Rayan series.	43·5
Yellowish stone			6·5
Light brown solid stone			10·5
Cement coloured soft clay			1·7
Cement coloured stone			12·5
			205·7
Bottom of boring 182·3 metres below sea-level.

The method employed in this boring was such as to bring up the material as a ground-up paste, an examination of which does not afford absolutely conclusive evidence as to the age of the rock. The absence, after the first 18·5 metres, of sand or pebbles, common throughout the alluvial deposits of the Fayûm, suggests that the base of these beds was reached at that depth, but from this evidence alone it would perhaps hardly be satisfactory to conclude that the underlying 112·5 metres were entirely Eocene. Considering, however that in the two deep ravines of El Bats and El Wadi the underlying Eocene is very commonly exposed at an average depth of some 15 metres below cultivation level, it is highly improbable that in the centre of the area, at Medinet el Fayûm, the alluvial deposits greatly exceed the same thickness. To classify the 112·5 metres of marly clays as alluvium would give the latter a total thickness of 131 metres and would mean that over an extremely restricted area the Eocene rocks had been denuded to such an extent that the floor of the depression lay 108 metres below sea-level. The ground-up samples of rock closely resemble what might be expected from the clays and marls forming the Ravine beds and in all probability the greater part of the 112·5 metres belong to that series. The harder stone met with at 131 metres, which, with the exception of a band of soft clay, continued down to the bottom, must be regarded as belonging to the underlying Rayan series.

Dr. Blanckenhorn’s Fault theory.Dr. Blanckenhorn, in a paper published in 1901[29] dealing with the Pliocene and Pleistocene of Egypt, describes the Fayûm as a triangular depression bounded on all sides by faults. The position of these bounding faults, as well as of numerous others more or less parallel to the north shore of the Birket el Qurûn, is shown on an accompanying map[30] and in a section drawn from Abshawai to the summit of the plateau north of the lake.[31] Stratigraphical evidence, based on the supposed identity of certain strata in different localities, is brought forward in support of these faults, the author finally stating that the production of the Fayûm is clearly and distinctly to be referred to tectonic movements.

Our conclusion, formed after an examination of the region in some detail, is so diametrically opposed to the above, that it may be worth while to state here the evidence which we consider sufficient to refute the existence of the particular faults described by Blanckenhorn.

Blanckenhorn’s fault-lines lie for the most part within the area covered by the alluvial deposits and the water of the lake, so that for want of exposures it is in most cases impossible to directly disprove their existence, although strong presumptive evidence against them can be adduced. The fault along the east side, however, is shown as closely following the junction line of the desert and the cultivated land, but everywhere along this line we found the marls and limestones of the Ravine beds passing regularly from the desert under the cultivated lands, without any sort of break or dislocation. Moreover, an examination of the desert ridge to the east disproved the existence of any faulting on the desert side, while the appearance of the same beds in the ravine of El Bats, a few kilometres to the west, proved the continuity of the beds under the cultivated alluvium in this direction. Certainly no fault exists along this side of the Fayûm. Similarly with regard to the fault shown as running from the west end of the lake along the west side of the Fayûm cultivation into the basin of Gharaq; although the desert margin along this side of the Fayûm cultivation has not been so closely surveyed as that on the east side, no evidence in favour of the existence of faults was met with in the particular localities examined. With regard to the third main bounding fault, considered by Blanckenhorn to run throughout the length of the Birket el Qurûn and to be continued eastwards, possibly to the Nile Valley and at least to join the fault on the east side of the cultivation, we need only say that an examination of the desert near Tamia disproves its existence at that end; while it is difficult to imagine that a fault could traverse the lake from end to end without revealing its presence in the island Geziret el Qorn or in one or other of the promontories which jut out so far into the lake from its northern shore. Everywhere the strata are undisturbed and occupy their normal stratigraphical level and position.

Let us finally examine the series of more or less parallel faults stated to exist between the island and the northern shore of the lake, and on the mainland to the north and south of Dimê. Dr. Blanckenhorn publishes a detailed section (op. cit., fig. 2., taf. XIV) showing the positions of these step faults and their effect on the various strata through which they cut. Fortunately, in this neighbourhood the stratigraphical succession is well exposed and the presence or absence of faults become matters of easy determination. The sequence of beds from south to north is normal and uninterrupted and our interpretation of the area is shown in the accompanying sections (Plates XIX, XXII, and fig. 4). We have no hesitation in saying that such faults as those shown on Blanckenhorn’s section do not exist. Their insertion appears to be the outcome of an error in the correlation of strata at the three points Abshawai, Geziret el Qorn and Dimê. The bed capping the island is not identical with that forming the plain to the north of Dimê, although shown to be such on the section under discussion.

In a later publication[32] Blanckenhorn admits being in error in his correlation of the different beds in the localities in question and completely withdraws his former statements that the depression owes its existence to fracture and subsidence. The faults shown on his detailed section from Abshawai to Qasr el Sagha are admitted to be non-existent and in this retraction we may presumably include the remainder of the faults described by the same author, as the evidence for them is of a still less satisfactory nature.

In a wind-swept desert area like the Fayûm the slightest dislocations are as a rule markedly obvious, and faults of any magnitude could scarcely escape detection. Over the greater part of the region every bed is laid bare on the surface and can be minutely examined; while the marked irregularity of the escarpments afford sections cut through the different series in every direction. Some areas, however, are covered with superficial deposits, which more or less effectually obscure the underlying rocks; for instance, on the east side a large part of the central floor is hidden by the cultivated alluvium and by the water of the lake; in the south a considerable proportion of the floor of Wadi Rayan is buried under accumulations of blown sand; and again large areas on the north, west, and south-west sides are obscured by a superficial covering of loose gravel. But as already mentioned, there is no reason to suppose that faults of any importance exist within the areas thus partly obscured. The cultivated lands and the Birket el Qurûn do not occupy low areas produced by faulting but, as shown above, owe their positions entirely to the original northerly dip of the strata and to subsequent erosion.

Numerous small faults effects local.We have already stated that small local faults occur in various parts of the Fayûm and some of these may be specially mentioned. The most important is about 10 kilometres N.N.E. of Qasr el Sagha; the line of fault lies nearly north-west and south-east, has a length of six or seven kilometres, and affects both middle and upper Eocene beds; at its northern end the fault passes into a fold before finally dying out. Some of the Upper Eocene sandstones are hardened and silicified and form a succession of black knobs along the line of disturbance. To the south of these the axis of dislocation bends slightly eastwards and takes the form of a sharp fold; further south it again becomes a true fault, flanked by a line of highly tilted beds along its south-west side. The effects of this fault are very marked locally but entirely restricted to a limited area. The most important is the breaking of the continuity of the escarpment of the Qasr el Sagha series; the line of cliffs formed by those beds is a very marked topographical feature and the fault in question causes a lateral displacement of seven kilometres.