[Illustration: PLATE I.
NORTH SIDE OF THE BIRKET EL QURUN, LOOKING WEST.]
SURVEY DEPARTMENT,
EGYPT.
* * * * *
THE TOPOGRAPHY AND GEOLOGY
OF THE
FAYUM PROVINCE
OF EGYPT
BY
H. J. L. BEADNELL, F.G.S., F.R.G.S.
[Decoration]
CAIRO
NATIONAL PRINTING DEPARTMENT
1905.
CONTENTS.
* * * * *
INTRODUCTION.
PAGES.
Surveying operations. Soil survey. History of discovery of
Fayûm vertebrate fauna 9
PART I.—TOPOGRAPHY AND STRUCTURAL GEOLOGY.
SECTION I.—CULTIVATED LAND—
Area. Composition and character of alluvial soil. Connection
with Nile Valley. Bahr Yusef and canal system. Ravines.
Alluvial deposits of Lake Moeris and prehistoric lake.
Increase of cultivated lands 11
SECTION II.—THE BIRKET EL QURUN—
Site, depth and dimensions. Remnant of Lake Moeris. Continual
shrinkage of lake. Deposition of sand in lake at present day.
Salinity of lake. Possible underground outlets. Currents 12
SECTION III.—THE SURROUNDING DESERT REGION—
Area and limits of Libyan Desert described. Rocks forming the
area. Importance of dip. Chief causes of origin of Fayûm 14
SECTION IV.—WADI RAYAN AND NEIGHBOURHOOD—
Colonel Western’s survey. Sir William Willcocks’ report.
Borings. Details of proposed reservoir. Schweinfurth’s
estimate of salt content. Willcocks’ “Assuan Reservoir and
Lake Moeris.” Detailed geological examination not yet
undertaken. Traverse from Nile Valley through Wadi Muêla and
Rayan to Gharaq. Warshat el Melh and springs of Wadi Muêla.
Der el Galamûn. Pass from Muêla to Rayan. Sand accumulations.
Wadi Korif. Springs of Wadi Rayan. Analyses and output of
water. Geological succession in Wadi Rayan. General geology of
floor and bounding walls. Ridge separating Rayan and Gharaq.
Apparent absence of Nile deposit and freshwater shells in Wadi
Rayan. Question of leakage through ridge. Permeability of Rayan
if used as a reservoir. Salinity of water 16
SECTION V.—CENTRAL AREA OF THE REGION—
Area and features. Dip-slope of surface. Drainage basins of
central plain. Pools formed by rainfall. Tamarisk growth. The
eastern area covered by alluvium. The bounding plateau to the
north. Ghart el Khanashat dunes 24
SECTION VI.—THE RIDGE SEPARATING THE NILE VALLEY AND FAYUM—
Width and highest points. Strata forming ridge. Gravel
terraces. Low points of ridge. Original access of Nile waters
to depression. Formation of lake and deposition of sediment
in Fayûm 25
SECTION VII.—THE NORTHERN DESERT REGION—
Escarpments and plateaux. Extreme west and south-west limits
of area. Ferruginous silicified puddingstone of ancient rivers.
Jebel el Qatrani. Widan el Faras. Elwat Hialla. Garat el Gindi.
Garat el Faras 26
PART II.—TECTONICS.
SECTION VIII.—FAULTING AND FOLDING—
Origin of depression. Evidence in drainage ravines El Bats and
El Wadi. Deep boring at Medinet el Fayûm. Dr. Blanckenhorn’s
theory that depression owes its origin to extensive fault
system. Fault theory disproved. Fault N.N.E. of Qasr el Sagha.
Numerous local strike faults of small throw. Occasional
influence of fractures in determining escarpments 29
PART III.—GEOLOGY.
SECTION IX.—GENERAL AND CLASSIFICATION OF STRATA—
Depression cut out in sedimentary rocks. Local lava flows.
Dip. Oldest beds the Nummulites gizehensis limestones of
Middle Eocene. Fluviomarine series of Upper Eocene and
Oligocene age. Absence of Miocene strata. Pliocene,
Pleistocene and Recent. Table showing succession and
classification of strata 33
SECTION X.—MIDDLE EOCENE—
A.—_Wadi Rayan Series._—Work of Schweinfurth and Mayer-Eymar.
Section at entrance to Wadi Muêla on Nile Valley side. Strata
of cliffs near Der el Galamûn. Detailed section measured at
Jebel Rayan. Mayer Eymar’s section in Wadi Muêla 35
B.—_Ravine Beds._—In ravines of El Bats and El Wadi. Relation
to underlying series seen at Gar el Gehannem. Section at Gar
el Gehannem. Fauna of strata. In ravines unconformably
overlain by Pleistocene, etc. Form plain bordering cultivation
on east side. Extension into Nile Valley. Occurrence at Sersena
and Tamia. Forming base of Geziret el Qorn and lower part of
northern escarpment of Birket el Qurûn. West end of lake. Hard
siliceous bands give rise to horns or promontories of lake.
Ravine Beds in the Medinet el Fayûm boring. Thickness 37
C.—_Birket el Qurun Series._—Homotaxial with quarried
limestones of Cairo. Foraminiferal beds. Extension of series.
Section at Ezba Qalamsha. Section north of Lahûn pyramid. East
of Sersena and north-east of Rubiyat. Section 17 kilometres
28° N. of E. of Tamia. Series characterized by large globular
concretions. Development and fauna in Geziret el Qorn.
Zeuglodon remains. Profile at Geziret el Qorn. Rich molluscan
fauna. Section on mainland opposite Geziret el Qorn. Section at
west end of Birket el Qurûn. Formation of earth-pillars.
Extension west of the lake. Development of the series in the
Zeuglodon Valley. Abundance of skeletons of whales. Molluscan
fauna. Pseudomorphs in celestine. Hill mass south of the
Zeuglodon Valley. Junction of Birket el Qurûn series with
overlying stage 41
D.—_Qasr el Sagha Series._—Equivalent of the Upper Mokattam
of Cairo. Greater development in Fayûm. Vertebrate fauna of
series. Schweinfurth’s original discovery of cetacean remains.
Recent discovery of land and marine mammals. Extension of
series generally. N.N.E. of Tamia. At Garat el Faras. In the
cliffs north of the Birket el Qurûn. Detailed section near
ruin of Qasr el Sagha. At Gar el Gehannem and westwards. Land
animals floated out from land by river currents. The series a
littoral deposit. Lignitic beds and thin seams of coal 49
SECTION XI.—UPPER EOCENE — LOWER OLIGOCENE—
E.—_Fluvio-marine Series._—Nature of sediments, Interbedded
basalts in upper part. Character of its invertebrate fauna.
Conditions of deposition of series. Continuance of similar
conditions to Miocene and even Pliocene times. Bone-beds at
base of series. Association of skeletons of animals and forest
trees. Preservation of remains. Analysis of fossil bones.
Relation of Fluvio-marine series to underlying stage.
Characteristics of the group. Its development in the field.
Its slight development at Elwat Hialla. Section near Elwat
Hialla. Constant northerly dip. Organic (molluscan) remains 9
and 14 kilometres north of Qasr el Sagha. Detailed section
from near Qasr el Sagha to Widan el Faras. Determinations of
mollusca from the series. Tripartite character of the series
west of Widan el Faras and Qasr el Sagha. Occurrence of
calcite, gypsum and chalcedony. Tabular chert and flint.
Ancient workings. Extent of basalt. Silicified trees 53
F.—_Age of the Fluvio-Marine Series._—Difficulty in the
determination of age owing to paucity of fossils. Zittel’s
tabulation of “Schichten von Birket el Qurûn” as Oligocene.
Mayer-Eymar’s age determinations. Schweinfurth’s comparison
of the series with the Scutella beds of Der el Beda near
Cairo. Blanckenhorn’s determinations. The stratigraphical
position of the series and relationship to Qasr el Sagha
series. Stratigraphically lower than the Lower Miocene of
Mogara. Whole complex in all probability of Upper Eocene and
Oligocene age, the transition being at or near the basalt
sheets 63
G.—_The Position of the Land Mass from which the Mammals
were derived._—Proximity of continental land. Absence of
branches on fossil trees. Massif of Abu Roash perhaps an
island to the north. Extension of Eocene sea. Continual
retreat of the sea northwards. Rivers emerging from the land.
Number and positions of such rivers doubtful. Evidence for
river passing from the modern oasis of Baharia through Gar el
Hamra to the Fayûm. Lacustrine and fluviatile deposits along
the course. Huxley’s theory of immigration and invasion of
animals into Africa. Fayûm animals belong to an extinct African
fauna of Tertiary times. Contains the earliest and most
primitive forms of elephants and other groups. Emigration and
immigration. Prof. Osborn’s theory of the African continent as
a centre of radiation. Confirmation by the Fayûm mammal
discoveries. List of new species obtained from the Fayûm 65
H.—_The Absence of Miocene deposits in the Fayûm._—The Fayûm a
land area in Miocene times. Miocene deposits of Mogara.
Lithological similarity. Probable persistence of geographical
conditions 71
SECTION XII.—PLIOCENE—
J.—_Marine deposits: Middle Pliocene._—Marine deposits of
Sidmant with typical Middle Pliocene mollusca. Relation of
these deposits to the gravel terraces as yet unknown though
important 71
K.—_Borings on Rock Surfaces; of doubtful age._—Apparently
due to marine boring mollusca. No exact evidence as to age.
(α) Low level borings from zero to 20 metres above sea-level.
(β) High level borings at 112 metres above sea-level. Limited
occurrences of borings 71
L.—_Gravel Terraces:? Upper Pliocene._—Well marked terraces
of gravel up to 170-180 metres above sea-level. East of Sêla.
Character of deposit. East of Sersena and Roda. N.N.E. of
Tamia, N.N.E. of Garat el Faras, east and north-east of Garat
el Gindi. Relation to different series. Character of gravels
at Elwat Hialla. West of Elwat Hialla gravel terraces almost
completely removed by denudation. Traces near Widan el Faras
and near Garat el Esh. Height of terraces in latter locality
determined as 170 metres above sea-level. Terrace marks shore
line of great sheet of water, whether freshwater or marine.
The great plains of the Fayûm possibly in part plains of marine
denudation 73
M.—_Gypseous Deposits: probably dating from the close of the
Pliocene._—Extension in Nile Valley and Fayûm. Section at
Medum. On the east side of the Fayûm. Gypsum cemented
conglomerate. Close connection with upper part of gravel
terraces 77
N.—_Summary of Pliocene Period_ 78
SECTION XIII.—PLEISTOCENE—
Earliest existence of a freshwater lake. Probably not a
remnant of the Pliocene sea or lake in which gravel terraces
were formed. Intermediate denudation of area. Date of earliest
entry of Nile waters doubtful. Freshwater lake of Nile Valley.
Drainage down the Nile Valley and establishment of river.
Breaking down of gravel ridge separating the valley and the
Fayûm. Entrance of flood waters. Formation of lake and
deposition of sediment. Subsequent disconnection of Nile Valley
and Fayûm owing to erosion of river bed. Rise of Nile in
prehistoric and historic times. Reconnection. Geological
evidence for the existence of great freshwater Pleistocene
lake. Position and dimensions. Fossil fauna of the lake, and
its difference from all other Egyptian faunas. Blanckenhorn’s
conclusions 79
SECTION XIV.—RECENT 81
O.—_Prehistoric._—Abundance of worked flints. Shores of lake
inhabited by Neolithic and probably prehistoric man. Tamarisk
remains. Probable age of flints anterior to Egyptian historic
period 82
P.—_Historic._—Relations of the Nile Valley river system and
the Fayûm. Lake Moeris a regulator of the Nile floods. Brought
under control in XIIth dynasty. Early references to Lake
Moeris. Its position disputed in modern times. Linant de
Bellefonds’ assertion disproved by Sir Hanbury Brown.
Archæological evidence for the site. Present day fauna of the
Birket el Qurûn. Modern deposits. Blown sand. Erosion 82
APPENDICES 87
1. Previous literature relating to the Fayûm 87
2. Fayûm lamellibranchs mentioned in Oppenheim’s “Zur Kenntnis
alttertiärer Faunen in Ægypten.” 89
INDEX 91
LIST OF ILLUSTRATIONS.
* * * * *
PHOTOGRAPHS.
PLATES. PAGE.
I. — North side of the Birket el Qurûn,
looking west _Frontispiece._
II. — Bahr Yusef at Lahûn before entering
the Fayûm _to face_ 11
III. — El Wadi, Ravine near Qasr Gebali „ 19
IV. — Western extremity of the Birket el Qurûn „ 29
V. — Alluvial deposits overlying marly
limestones (Ravine Beds) in El Wadi,
Ravine near Qasr Gebali „ 37
VI. — Escarpment of the Birket el Qurûn series
near the western end of the lake „ 41
VII. — Weathered concretionary sandstone
(Birket el Qurûn series) on north shore,
near Geziret el Qorn „ 45
VIII. — Middle Eocene escarpment (Qasr el Sagha
series) 12 kilometres west of Qasr el
Sagha „ 49
IX. — Upper beds of Fluvio-marine series with
basalt cap, looking west from the
eastern extremity of Jebel el Qatrani „ 53
X. — El Qatrani range from the south-east „ 57
XI. — Silicified trees of Fluvio-marine
series, 4½ kilometres north of Qasr el
Sagha „ 63
XII. — Raised Beach unconformably overlying
Middle Eocene limestones (Birket el
Qurûn series) in the desert east of
Sersena „ 69
XIII. — Borings in false-bedded sandstone, 2
kilometres south of Dimê „ 73
XIV. — Pleistocene lacustrine clays with
tamarisk stumps _in situ_ at 50 metres
above the present surface of the Birket
el Qurûn „ 77
XV. — Isolated sand-dune near Gar el Gehannem „ 81
XVI. — The Birket el Qurûn near the western end „ 85
PLANS.
XVII. — General Map of the Fayûm depression, with Wadi Rayan
and Wadi Muêla, 1/250000 end
XVIII. — Map of the area north-west of Qasr el Sagha, showing
principal bone-bearing localities, 1/50000 „
SECTIONS.
XIX. — From the Birket el Qurûn through Dimê and Qasr el
Sagha to the summit of Jebel el Qatrani end
XX. — From Wadi Rayan to the summit of the escarpment
north of Gar el Gehannem „
XXI. — The Desert Ridge separating the Nile Valley and
the Fayûm „
XXII. — From Sidmant el Jebel in the Nile Valley through
Medinet el Fayûm to the summit of Jebel el Qatrani,
near Widan el Faras „
XXIII. — Middle Eocene escarpment near Qasr el Sagha „
XXIV. — From Garat el Esh to summit of Jebel el Qatrani „
FIGURES (IN THE TEXT.)
1. — Fault near Qasr el Sagha 32
2. — Section at Gar el Gehannem, showing the relation of
the Wadi Rayan series to the Ravine Beds 38
3. — Sketch-section across El Bats, one kilometre west
of Sêla 40
4. — Profile of beds of Geziret el Qorn 44
5. — Section of cliffs, western end of the Birket el-Qurûn 47
6. — Probable course of chief river of Upper Eocene and
Oligocene times 67
7. — Block of sandstone pierced by numerous borings 72
8. — Sketch showing relations of the Eocene to Pliocene
gravel terraces on the east side of the Fayûm 74
9. — Sketch-section through the summit of the Fayûm
escarpment at Elwat Hialla 76
10. — Sketch-map showing approximately the site of
Lake Mœris 83
INTRODUCTION.
* * * * *
The geological survey of the desert surrounding the Fayûm was
commenced in October 1898. At that time the area, although so near
to Cairo, was little known; the Rohlfs Expedition maps marked the
region as “unexplored,” and in fact with the exception of a
publication by Schweinfurth, who had traversed the region from north
to south, _via_ Qasr el Sagha and Gar el Gehannem to Rayan, there was
little information obtainable. The area being of considerable size
(12,000 sq. kilom.) and almost unexplored, both geologically and
topographically, the primary object was to construct as rapidly as
possible a general map of the depression, at the same time laying down
in broad outline the chief geological formations and trusting to future
opportunity to examine in more detail places of special interest.
Commencing work at Sêla, on the eastern side of the depression, the
survey was carried northwards along the east side of the cultivated
lands and thence through the northern desert, up to the summit
of the depression. After mapping westwards as far as the isolated
hill-mass of Gar el Gehannem the work was temporarily suspended until,
in the spring, the narrow defile of Wadi Muêla, and the Wadi Rayan,
forming the southern part of the Fayûm depression, were provisionally
examined.
In January 1901, samples of soil and water from the cultivated lands
were collected as an experimental soil-survey, and the results have
been published.[1]
During the winter’s work of 1902-03 a traverse was carried from Gar
el Gehannem in a south-west direction through a hitherto unexplored
part of the depression. On reaching a point midway between Cairo
and the oasis of Baharia a connection was made eastwards to Wadi
Rayan. In the winter of 1903-04 further exploration was carried out
in the neighbourhood of Gar el Gehannem.
It will be convenient here to briefly relate the history of the
discovery of the remarkable series of new and extinct animal forms, the
recovery of which from the Fayûm deposits has created such widespread
interest in the zoological world. When Schweinfurth crossed the region
in 1879 he obtained fossil bones, which were examined and determined
by Dames to be the remains of cetacea of the genus _Zeuglodon_,
from certain beds of the escarpment west of Qasr el Sagha; these,
it is believed, were the earliest vertebrate remains obtained from
the Fayûm. During the early part of the survey of the district,
remains of fish and crocodiles were frequently found in one of the
beds of the Middle Eocene, probably on the same horizon as that
from which Schweinfurth had collected. Fragments of bone were also
commonly met with on a much higher horizon (_i.e._, near the base
of the Fluvio-marine series) but nothing of particular interest
was obtained, as no detailed search could be made at that time. In
April 1901, during the survey of the western end of the Birket el
Qurûn, some of the localities found to be bone-bearing in 1898 were
re-visited in company with Dr. C. W. Andrews, who was in Egypt at the
time and had accompanied the survey in order to obtain specimens of
jackals, hares, etc., for the British Museum, in connection with the
forthcoming work on Egyptian mammals. In one of these Dr. Andrews
picked up several vertebrae which turned out to belong to a new
species of _Pterosphenus_.
Further north, when descending the Middle Eocene escarpments at a place
not previously examined, we crossed the outcrop of the bone-beds at a
point where a considerable number of mammalian and reptilian bones lay
exposed on the surface, many in an excellent state of preservation. The
importance of the find was evident, and a short examination of the
material on the spot enabled Dr. Andrews to pronounce the discovery
to be of the highest importance from a palaeontological point of view.
Some three weeks’ work in the immediate neighbourhood resulted in
a very good collection of vertebrates from the Middle Eocene beds,
including several new genera afterwards described[2] under the names of
_Eosiren_, _Barytherium_, _Mœritherium_, _Gigantophis_, etc. Moreover,
a fossil tooth brought in by one of the camelmen from a point several
kilometres to the north led to a careful examination of the lower beds
of the overlying Upper Eocene formation, which resulted in obtaining
well-preserved remains belonging to a new genus, since described as
_Palaeomastodon_. All the material so far obtained was taken home to
be worked up and determined at the British Museum and a preliminary
description was published by Dr. Andrews in the Geological Magazine.
In the winter of 1901-02 the survey of the Fayûm was resumed
with the special intention of following up the highest beds,
those in which _Palaeomastodon_ had been found. Continued search
westwards eventually led to the discovery of the remains of a large
and remarkable horned ungulate (_Arsinoitherium_), a preliminary
notice[3] of which was published in the spring of 1902. Shortly after,
the remains of several new smaller mammals and reptiles (_Phiomia_,
_Saghatherium_), including the shell of a large land tortoise
(_Testudo Ammon_), were obtained[4]. Further work in the winters
of 1902-03-04 led to a great deal more material being obtained[5],
mostly of course belonging to the same species, but including some
new genera _Geniohyus_, _Megalohyrax_, _Pterodon_.
The amount of palaeontological material is now so large that the
Egyptian Government has arranged with the Trustees of the British
Museum for the publication of the whole in a monograph to be issued
by the Trustees. The present report, therefore, deals only with the
geology and topography of the district.
[Footnote 1: A. LUCAS, _A preliminary investigation of the Soil and
Water of the Fayum Province_; Survey Dep., P.W.M. Cairo, 1902.]
[Footnote 2: ANDREWS, _Extinct Vertebrates from Egypt_. Parts I
and II. Geol. Mag. N. 8. Dec. IV, Vol. VIII, Sept. and Oct. 1901,
pp. 400-409 and 436-444.]
[Footnote 3: BEADNELL, _A Preliminary Note on Arsinoitherium Zitteli,
Beadn._ Survey Dept. P.W.M., Cairo, 1902. See also _A New Egyptian
Mammal (Arsinoitherium) from the Fayûm_. Geol. Mag. N.S. Dec. IV,
Vol. X. Dec. 1903, pp. 529-532.]
[Footnote 4: ANDREWS and BEADNELL, _A Preliminary Note on Some New
Mammals from the Upper Eocene of Egypt_. Survey Dept. P.W.M., Cairo,
1902.]
[Footnote 5: ANDREWS, _Notes on an Expedition to the Fayûm, Egypt,
with Description of some New Mammals_. Geol. Mag. N.S. Dec. IV,
Vol. X. Aug. 1903, pp. 337-343. Also _Further Notes on the Mammals
of the Eocene of Egypt_ (Parts I, II, III). Geol. Mag. N.S. Dec. V.,
Vol. I. March, April, May 1904.]
[Illustration: PLATE II.
BAHR YUSUF AT LAHUN BEFORE ENTERING THE FAYUM.]
PART I.
=TOPOGRAPHY AND STRUCTURAL GEOLOGY.=
* * * * *
The Fayûm, a large circular depression in the Libyan Desert, is
situated immediately west of that part of the Nile Valley lying
between Kafr el Ayat and Feshn (Plate XVII.)
The depression, which has an area, roughly speaking, of 12,000
square kilometres, is primarily divisible into three distinct
parts—cultivated land, lake, and desert.
SECTION I.—CULTIVATED LAND.
The cultivated land has an area of about 1,800 square kilometres and,
with the exception of the lake and part of the Wadi Rayan, occupies
the lowest part of the depression. Cultivation is necessarily strictly
limited to the area covered with alluvial soil. The latter, for the
most part identical in origin and composition with the river-alluvium
of the Nile Valley, covers a leaf-shaped tract between the bounding
desert on the east side and the lake (the Birket el Qurûn) on
the north-west. The easterly and central part of the cultivated
area forms a more or less level table-land, from which the ground
slopes gently away, especially on the north side, where the slope is
towards the lake and very marked. The cultivated land of the Fayûm
is directly connected with that of the Nile Valley by a narrow strip
of low ground, a natural passage through the desert separating the
Nile Valley and the depression of the Fayûm. Through this gap runs
the natural canal known as the Bahr Yusef, which is practically the
sole source of water in the Fayûm and irrigates the entire district.
The canal leaves the Nile Valley at Lahûn (Plate II), and follows a
somewhat serpentine course through the desert for about 5 kilometres,
irrigating a narrow strip of land on either side, which at Hawara
rapidly broadens out into the wide cultivated area of the Fayûm. Once
within the latter, the Bahr Yusef gives off numerous subsidiary canals
which traverse the country in all directions, constantly splitting up
into smaller branches until the water-supply is divided throughout the
whole area. With the exception of the self-contained basin of Gharaq,
on the south side of the Fayûm, the entire district drains into the
Birket el Qurûn, which occupies the lowest part of the depression,
to the north of the cultivation. The basin of Gharaq is irrigated by
the Bahr el Gharaq, a canal which takes off from the Bahr Yusef soon
after the latter enters the Fayûm[6].
The cultivated land of the Fayûm is traversed by two main ravines,
cut down in many places to the Eocene limestone below the alluvium
(Plates III and V.) At the present time these ravines carry canals
for irrigating the lower parts of the district, and also act largely
as drains to the higher lands. They were probably initiated by the
escape of water through breaches in the Bahr Yusef during flood time,
and have since been deepened to their present dimensions.
In addition to the main central cultivated area, the soil of which,
as mentioned above, is essentially identical with that of the Nile
Valley, large tracts of the surrounding country, more especially on
the north, north-west, and west sides, are also covered with alluvial
deposits. These latter, which include sands, sandy clays, and clays
of a quite distinct type, represent the slowly formed accumulations
of the quieter and more remote parts of the ancient Lake Moeris (and
the earlier prehistoric lake). The material was mostly derived from
the Eocene strata which formed the shores of the lake, augmented no
doubt by a certain amount of very fine sediment drifted from the Bahr
Yusef, and by sand blown in by wind.
It is noticeable that the thickest and most sandy deposits occur near
the borders of the lake site; when close under the Eocene cliffs,
as along the north side above the Birket el Qurûn, the deposits
closely resemble those of the latter. The finer more calcareous beds
occur further out and the true marls were accumulated only at some
distance from the shores of the lake.
When in Ptolemaic times the lake became reduced to a fraction of
its former size, large areas covered by these lacustrine clays were
exposed and some portions were brought under cultivation. Subsequently,
however, all these outlying districts were abandoned and became
absorbed by the surrounding desert, until in modern times the
cultivation was restricted to the central portion of the old lake
bed, a portion almost identical with the area over which true “Nile
Mud” had been deposited.
The construction during recent years of extensive irrigation works
in the Nile Valley has made it possible to largely augment the
water-supply of the Bahr Yusef to the Fayûm. High level canals are
being cut in various parts of the district and already large areas of
desert covered by these lacustrine deposits have been brought under
cultivation, notably to the north of Tamia and in the neighbourhood
of Qasr Qurûn. The approximate area covered with lacustrine deposits
can be seen on the map and with a sufficiency of water probably the
greater part of this area could be utilized, though the exact value
of the soil compared with Nile deposit remains to be determined.
SECTION II.—THE BIRKET EL QURUN.
The lowest part of the depression, lying immediately to the north-west
of the cultivation, is occupied by a sheet of water of considerable
size, known as the Birket el Qurûn.[7] The lake, which has a length of
40 kilometres, and a maximum breadth under ten, covers at the present
time an area of about 225 square kilometres. Sir Hanbury Brown obtained
no sounding exceeding 5 metres in crossing the lake to Dimê, but
according to the fishermen the depth increases towards the south-west.
Its long axis lies nearly east and west, and while on the north it is
entirely[8] bordered by desert, along a large part of the south side
the cultivated land approaches its shore, although even here a large
area actually bordering the lake is waste salty land as yet unfit for
cultivation. As already mentioned, with the exception of the Gharaq
basin, the lake receives the whole drainage from the cultivated lands.
The Birket el Qurûn is the existing remnant of the ancient prehistoric
lake which covered a large part of the floor of the Fayûm depression,
and which in historic times was converted into an artificially
controlled sheet of water—the celebrated Moeris—by Amenemhat I
and his successors in the XII Dynasty.
Lake Moeris, being used as a regulator of excessively high and low
Nile floods,[9] was of the greatest importance in connection with
the irrigation of the Nile Valley. In more recent times, apparently
under the Persians or Ptolemies according to Flinders Petrie,[10]
Lake Moeris ceased to perform its function of regulator; since that
time all water, except that required for irrigation of the reclaimed
land, being carefully excluded, the surface of the lake has continually
and gradually sunk to its modern dimensions.[11]
Lacustrine deposits, showing approximately the actual limits of the
ancient Fayûm lake, can be traced over wide areas of now barren
desert; these will be more fully dealt with later. The present
lake-level is still continually sinking owing to an improved system
of irrigation, by which a constantly decreasing amount of waste
water drains into the lake. Its average annual fall has, during the
last decade, been nearly half a metre,[12] and the slope of the land
being very gradual, large areas have been reclaimed during the last
few years, though whether the advantages derived from this constant
lowering of the lake are not more than balanced by certain drawbacks
is somewhat doubtful.[13]
With the new areas now being brought under cultivation the amount
of drainage water finding its way into the lake will increase and
the fall be checked. At the beginning of 1904 the level was markedly
higher than in the previous winter, and a difference of even half a
metre alters the shore line to a considerable extent, owing to the
flatness of the land by which the lake is for the most part bounded.
Although under the present desert conditions practically no material
from the surrounding desert is washed into the lake, doubtless a
considerable amount of fine dust and sand is carried into it by the
wind, especially during the violent sandstorms which occur frequently
in the locality. The high cliffs which bound the northern shore of
the lake throughout a portion of its length probably have the effect
of checking the velocity of both north and south winds, thus causing a
considerable amount of sand, which would otherwise be carried across,
to be dropped on its surface. This material, together with the fine
mud brought down by the canals on the cultivation sides, must have
an appreciable effect in raising the level of the bed of the lake.
The phenomenon of the extraordinary freshness of the water of the
Birket el Qurûn has been commented on by Schweinfurth, who shows
that the degree of concentration of salt in a lake whose volume
has been continually reduced, and to which salt has constantly
been added, should be many times greater than the actual existing
amount. An analysis[14] of the water at the west end of the lake
(where the concentration is greatest, owing to the distance from the
feeder canals) showed that the total salts amounted to only 1·34%,
of which 0·92% was sodium chloride. Dr. Schweinfurth[15] concludes
that the lake has a subterranean outlet, which alone would enable
it to maintain its comparative freshness.[16] In this connection
it is interesting to note the existence of distinct currents, which
may possibly be caused by such outlets, in certain localities on the
north side of the lake; and it is just possible that a careful survey
of the lake itself would not only prove the existence, but show the
exact position, of such underground outlets.
Most probably, however, the currents are simply local movements
produced by temporary differences of level, which might conceivably
be caused in such a large and comparatively shallow sheet of water,
varying considerably in salinity in different localities, by wind
and evaporation.
The comparative freshness of the lake and the possible presence of
underground outlets are of the highest importance in their bearing
directly on two of the most important questions in connection with the
proposed utilization of the Wadi Rayan as a reservoir, i.e. what the
leakage from such a reservoir would be and to what degree of salinity
its water would attain.
SECTION III.—THE SURROUNDING DESERT REGION.
With the exception of the lake and the cultivated area the depression
is practically entirely desert. The southern and south-western parts
include the wadies Rayan and Muêla, where freshwater springs occur,
surrounded by areas covered by a good deal of wild scrub. Apart from
these, however, no springs occur outside the cultivated land.
The topography of the region is so intimately connected with its
geological structure that an adequate description of the former is
not possible without constant reference to the latter. Full geological
details will, however, be reserved for later consideration.
[Sidenote: Area and Limits.]
The part of the Libyan Desert dealt with in this report has, excluding
the cultivated land and the lake, an area of some ten thousand square
kilometres. While some portions have been examined and mapped in
detail, others are still very imperfectly known, especially on the
south and south-west sides. The irregular cliff-line forming the
southern boundary of Rayan and the adjacent wadis may be taken as our
limit in this direction, beyond lying an almost unbroken limestone
plateau rising gradually and continually to the south. On the north
and north-west the area under description is bounded by the southern
limit of the great undulating high-lying gravelly desert-plateau which
stretches with little change of character to the Mediterranean. On the
east side the Nile Valley forms a convenient though not altogether
natural boundary; while to the south-west our limit practically
coincides with the boundary of the depression, where the floor of
the latter insensibly merges into the general desert plateau.
[Sidenote: Rocks forming the Area.]
The rocks forming the area within the above limits are almost entirely
of sedimentary origin, the exception being a band of hard basalt
intercalated at the very top of the series and exposed only on the
extreme northernmost limit of the depression. The total thickness of
sediments, from the lowest beds exposed in the bottom of the Wadi Rayan
to the summit of the escarpments, a day’s march north of Tamia,
is some 700 metres. These beds include every kind of sedimentary
deposit—limestones, marls, clays, sandstones, sands and gravels,
forming an ever-changing succession of rocks, varying considerably in
hardness and capacity for withstanding the agents of denudation. It is
not too much to say that the coming into existence of the Fayûm, with
its plains, lowlying depressions, precipitous cliffs and escarpments,
was largely dependent on the existence of this variable series of
deposits.
Apart from the presence of sediments varying greatly in hardness
and durability, the fact that the whole of the rocks have an almost
constant northerly dip of two or three degrees is a point of prime
importance. So small a dip may be scarcely noticeable in any one place,
but over the large areas with which we have to deal its influence
on the position and level of any individual bed is very marked and
the topography of the region would have been essentially different
if the strata had been quite horizontal.
[Sidenote: Origin of the Fayûm.]
The unique character of the Fayûm is alone sufficient to show
that special causes have acted in its production. Two main causes
stand out:—(1) the presence of thick bands of comparatively
soft arenaceous and argillaceous strata breaking up the usually
continuous hard limestone of the Middle Eocene; (2) the effect of
the Nile Valley fault in lowering the whole of the western desert
(north of Assiut) relatively to the eastern. The former took place
as the result of changed geographical conditions on the continent
to the south at the time in question, with which however we need
not deal here. On a homogeneous mass of rock weathering has little
power to form depressions of any magnitude, and this is the cause of
the continuous unbroken plateau which stretches southwards from the
Fayûm, the underlying rocks being one continuous thick mass of hard
limestone. Wherever softer intercalations are present differential
weathering takes place, and all the great depressions of the Libyan
desert owe their origin to the presence of soft easily denuded strata;
if the great homogeneous mass of Nile Valley limestone had stretched
unchanged westwards, the oases of Farafra and Baharia would never
have existed. They owe their origin entirely to the presence of the
underlying saddle of softer Cretaceous rocks. Similarly if changed
conditions had not led to the deposition of soft beds of clay, marl,
and sandstone, the western plateau would have continued unbroken
northwards.
A comparison of the two sides of the Nile Valley between Cairo and
Assiut shows that the tectonic movements, which largely determined the
existence of the valley itself, resulted in a considerable lowering
of the rocks forming the western side. This was brought about by
differential movements along the north and south line or lines
of fault, and by the presence of an east to west monoclinal fold
which is especially well marked in the neighbourhood of Heluan. The
depressions of the Fayûm would doubtless have existed irrespective of
this general lowering of the western desert relative to the east, but
denudation would have required an additional period of many thousands
of years before the floor of the depression was low enough to allow
of its actual connection with the Nile river.
As it has been maintained that the Fayûm is an area let down and
enclosed by faults, it may be mentioned here that all available
evidence points in an opposite direction; this question of faults
will however be dealt with in detail later. The influence of the Nile
Valley fault has been explained above and it must be remembered it
is one affecting not the Fayûm alone but the northern part of the
western desert as a whole.
For purposes of description it will be convenient to divide the whole
region into three parts: first, the southern portion, including the
wadis Muêla and Rayan; secondly, the central area, comprising the
extensive plain forming the floor of the depression as a whole, and
including the areas under cultivation and the Birket el Qurûn, as well
as the desert separating the Fayûm from the Nile Valley. Thirdly, the
northern portion, embracing all the rising ground between the floor and
the northern rim of the region. These areas will now be taken in order.
SECTION IV.—WADI RAYAN AND NEIGHBOURHOOD.
This part of the Fayûm is of special interest in consequence of
its possible future as a reservoir. Although the area has not yet
been examined in detail by the Geological Survey it will be useful
to bring together all the information that is at present available.
[Sidenote: Colonel Western’s Survey.]
In 1882, as a counter-project to other irrigation schemes, Cope
Whitehouse suggested[17] utilising as a reservoir the Wadi Rayan,
a depression which had been referred to by Linant de Bellefonds.[18]
At the request of Sir Colin Scott Moncrieff the Government deputed
Colonel Western to make plans of the Wadi Rayan and surrounding country
and to ascertain the capacity of the depression and its capability
of being used as a reservoir. Liernur Bey under his direction
prepared a contoured map, and Colonel Western’s report, plans, and
estimates were published.[19] Some general details of the wadi and
surrounding hills are given and the detailed survey showed that the
30 metre contour line (above sea-level) enclosed an area of 706 square
kilometres (170,000 feddans). The lowest points of the depression were
found at 42 metres below sea-level. The sand, scrub and springs are
briefly referred to and the discharge of the latter is given as equal
to that of a very slow-going four inch hand pipe, the water running
out at about + 20 m. and disappearing in the sand. Wadi Muêla was
found to be separated from the Rayan depression by sandhills and rock
at a mean level of + 50 metres, the lowest point in Muêla being at +
25 metres. A line of levels was run from Rayan through Muêla to the
Nile Valley, the highest point crossed being at + 105 metres; for
fifteen kilometres the level was not below + 75 metres. In order to
find the most suitable passage for a canal to connect the Nile with
the Wadi Rayan two lines of level were made after a reconnaissance of
the hills near Sidmant el Jebel: the southern, from Ezba Menesi Ali,
near the Gharaq canal, to Mazana on the Bahr Yusef, being considered
the best. Along this line the highest point was only at + 44·7 metres
and the average + 35 metres along four kilometres. Borings were not
made here but judging from the surface excavation would be mostly
in soft limestone, sand, and conglomerate. A much shorter route is
from Deshasleh on the Bahr Yusef over the hills about 5 kilometres
to the south of Mazana or Sidmant into the Wadi Gharaq, a distance
of 30 kilometres. This route was not however levelled but is fairly
straight and apparently not much higher than the Mazana passage.
The survey of the + 30 metre contour line of the Wadi Rayan proved
that there were only two outlets into the Fayûm, both on the northern
side: these two openings are only from 400-500 metres wide and their
lowest points are not below + 25 or + 26 metres.
[Sidenote: Later Government Publications by Scott Moncrieff and
Willcocks.]
In 1889 Sir C. Scott Moncrieff published[20] a further note, in which
he briefly discussed the probable cost and benefits to be derived
from the suggested reservoir, concluding that at least the project
was one worthy of being thoroughly examined.
In 1894 the plans and designs in connection with the Wadi Rayan
were published[21] and the possibility of utilizing the Wadi Rayan
was examined by Sir William Willcocks, then Director General of
Reservoirs, from an engineering point of view, and the questions of
its probable cost and future utility were discussed. In this report
it is stated that the routes proposed by Colonel Western in 1888 pass
through salty marls and clays unsuitable for holding canals. Another
route is suggested, which after leaving the Nile Valley crosses the
high desert ridge in a straight line, passing through the so-called
Wadi Liernur (Wadi Lulu of Cope Whitehouse); this depression is 12
kilometres long and has its bed some 24 metres below the general
level of the desert. Plate 15 of the report shows the Wadi Rayan, the
deserts between it and the Nile Valley and the cultivated land. The
map was begun by Col. Western and completed by Willcocks. The lowest
point of Wadi Rayan is shown as − 42 metres and the depression is
separated from the Fayûm by a limestone ridge generally from + 34 to +
60 metres, except at two places where it falls to + 26 metres above
sea level on a length of 600 metres. Within the + 27 metre contour
line the wadi has an area of 673 square kilometres and a capacity of
18,743,000,000 cubic metres. Between it and the Nile Valley lie 30
kilometres of desert, of which 11 are occupied by a marked depression
discovered by Liernur Bey in 1887. At the extreme western edge of the
Nile Valley (here 20 kilometres wide) runs the Bahr Yusef. Comparing
the proposed Wadi Rayan reservoir and the ancient Mœris and allowing
for a difference of 4·5 metres between the levels of the Nile Valley
in B.C. 2,000 and to-day, Willcocks assumes that the high water mark of
Lake Mœris was at + 22·5 metres and its area 2,500 square kilometres,
against 673 square kilometres of the Wadi Rayan at + 27 metres. It
is pointed out that the ancient lake had the great advantage that in
those days the Bahr Yusef was an important branch of the Nile, if not
the main river itself, and the reservoir was connected with the Nile
by a natural ravine of great length and short breadth, across which
a massive embankment was thrown and destroyed annually, the surplus
water of high floods being stored for the deficiency of low floods.
The published sections along the lines of borings put down show the
different strata cut through by the proposed canal. The Nile Valley,
along the line of the inlet canal, consists of hard clay 6 to 10
metres thick, lying on coarse sand. Along the outlet canal sandy
clays and clays alternate to a depth of 10 metres. On entering the
desert sands and sandy conglomerate, with gypsum and salt, are met
with below the surface, then a yellow marl with salts, and finally a
plastic black clay overlying the Parisian limestone. These beds are
most extensive in the narrow neck of land between the Nile Valley and
the Fayûm and to some 10 kilometres to the south of it. They rise
to + 70 metres. There are some other marls inside the Wadi Rayan or
in the adjacent depressions and as they have to be traversed by the
canals form a serious factor, being easily dissolved in water; in
consequence Willcocks chose the alignment of the inlet canal along
the Bahr Belama where the extent of these beds would only be 2·5
kilometres against 9 kilometres on the alternative route marked on
the plan. A narrow neck of land, some 15 kilometres in length, runs
between the Fayûm and the depressions traversed by the proposed
Wadi Rayan canal; this neck is the continuation of the salty marls
and clays, but the limestone is near the surface and is overlain by
a thin deposit of sand and pebbles, with freshwater shells on its
northern slope at + 22·50 metres; the southern slope is entirely
devoid of them. Willcocks points out that it is evident the ancient
Mœris rose to + 22·50 metres but its water never penetrated into the
Wadi Rayan. The report goes into details of inlet and outlet canals,
discharge, necessary masonry works, cost, and compares the different
reservoir schemes.
After a careful review of the whole question, the scheme, while
considered perfectly feasible as far as available data went, was
abandoned by Sir William Garstin[22] in favour of the less costly
and more useful Nubian reservoir.
[Illustration: PLATE III.
EL WADI, RAVINE NEAR QASR GEBALI.]
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: Traverse from Nile Valley through Wadi Muêla to Rayan
and Gharaq.]
[Sidenote: Warshat el Melh in Wadi Muêla.]
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. 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.
* * * * *
[Footnote 6: For fuller details of the cultivated lands, water-supply,
etc., of the Fayûm, the reader is referred to the excellent description
by Sir Hanbury Brown in his work _The Fayum and Lake Moeris_, London,
1892.]
[Footnote 7: “The Lake of the Horns,” so called from the narrow
horn-like promontories which jut out into the lake on the north
side. Views of the lake are shown in Plates I, IV, XVI.]
[Footnote 8: This was the case until a year or two ago. At the
present time a limited amount of freshwater finds its way to the
area immediately north of the east end of the lake and small plots
are cultivated by the arabs.]
[Footnote 9: _Herodotus_, Book II; _Strabo_, Book XVII; and _Diodorus
Siculus_, Book I, Chap. LI. (See Brown op. cit. p. 19-22.)]
[Footnote 10: “_Hawara, Biahmu and Arsinœ_,” 1889.]
[Footnote 11: BROWN, op. cit. p. 95. As mentioned above in some areas
the cultivated land was formerly even more extensive than at present,
notably near the modern villages of Roda, Tamia, etc.]
[Footnote 12: For details of evaporation and level-records of the lake,
see Brown, op. cit. pp. 6-9, and P.W.M. annual reports.]
[Footnote 13: See WILLCOCKS’ _Egyptian Irrigation_, 2nd edition,
London, 1899.]
[Footnote 14: See _A Preliminary Investigation of the Soil and Water
of the Fayûm Province_, by A. LUCAS, Survey Department, Cairo, 1902.]
[Footnote 15: See Appendix II, _A Note by Dr. Schweinfurth on the
Salt in the Wadi Rayan_, in Willcocks’ _Egyptian Irrigation_,
pp. 460-465.]
[Footnote 16: The word “freshness” is used comparatively, as
the amount of salt is sufficient to make the water unpalatable or
unfit for drinking, except near the feeder canals. It is, however,
quite good enough for most culinary purposes, and camels will usually
drink from it, although it is not advisable to water the latter from
the lake either before or after a fatiguing desert march, as in such
cases the salinity of the water may have bad effects.]
[Footnote 17: “Bull. of the American Geographical Society, 1882,
pp. 22 and 24.”]
[Footnote 18: _Mémoires sur les travaux publics en Egypte_, Paris,
1873, pp. 53, 54.]
[Footnote 19: G. A. LIERNUR, COL. WESTERN and COL. SIR C. C. SCOTT
MONCRIEFF, K.C.M.G. _Notes on the Wadi Rayan_, Cairo, 1888.]
[Footnote 20: _Note on the Wadi Rayan Project_, Cairo, 1889.]
[Footnote 21: _Perennial Irrigation and Flood Protection in Egypt_,
by W. WILLCOCKS, M.I.C.E. Dir. Gen. of Reservoirs, with A Note by
W. E. GARSTIN, Under Secretary of State, P.W.M., Cairo, 1894.]
[Footnote 22: The engineering details of the Wadi Rayan reservoir
project have since been more fully discussed by Sir William Garstin
in his “_Report on the Basin of the Upper Nile_” Cairo, (pp. 6-9
Appendix I).]
[Footnote 23: A Note by Dr. SCHWEINFURTH on the Salt in the Wadi Rayan:
an appendix to _Perennial Irrigation_, etc.]
[Footnote 24: _The Assuan Reservoir and Lake Moeris_, London, 1904.]
[Footnote 25: The following analyses of the chief springs in the
Wadi Rayan, made by Mr. Lucas, Chemist to the Survey Department,
are of interest:—
-------------------------+---------------+--------------+-------------
| NORTH SPRING.| SOUTH SPRING.| EAST SPRING.
-------------------------+---------------+--------------+-------------
Matter In Solution | 398·8 | 350·8 | 811·6
| | |
Chlorine calculated as | | |
Sodium Chloride | 278·4 | 238·2 | 585·5
| | |
Sulphur Trioxide | | |
calculated as | | |
Sodium Sulphate | 62·9 | 53·9 | 126·2
The above figures are parts per 100,000 parts of water.
Although the above analyses prove the water to be of a very poor
quality for drinking purposes, compared with many of the wells
and springs of the oases, the water, which is quite clear, seemed
good. Except for its softness and somewhat ferruginous taste, it
is quite palatable, and on my last visit we used no other for five
days. The south spring was found to yield 21 litres and the north 6
litres per minute. The water of the third spring does not run.]
[Illustration: PLATE IV.
WESTERN EXTREMITY OF THE BIRKET EL QURUN.]
PART II.
=TECTONICS.=
* * * * *
SECTION VIII.—FAULTING AND FOLDING.
[Sidenote: 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.
[Sidenote: 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 } 43·5
}
Yellowish stone } Probably these 6·5
} limestones and
Light brown solid stone } occasional marls 10·5
} and clays belong
Cement coloured soft clay } to the Rayan series. 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.
[Sidenote: 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.
[Sidenote: 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.
[Illustration: FIG. 1.—Fault near Qasr el Sagha.]
In the neighbourhood of Qasr el Sagha and westwards for a considerable
distance, small strike-faults are of common occurrence in the beds
of the Qasr el Sagha series. As a rule these faults do not extend
more than a few hundred metres in length, while the down-throw seldom
exceeds two or three metres and in almost every case observed is to the
north. The hade may be 65° or more. Fig. 1 shows an example near Qasr
el Sagha. The most marked of these strike faults is seen to the east
of Garat el Esh; commencing a little to the north-east of that hill
it runs in a nearly due easterly direction till it cuts the cliffs of
the Qasr el Sagha series after some five kilometres. Its down-throw
is to the north and never exceeds a few metres; this small throw
is however sufficient to cause a marked displacement of the highest
bed of limestone forming the dip-slope surface of the plateau at the
summit of the Middle Eocene beds.
At first sight it might be suspected that the very irregular trend
of the different escarpments throughout the Fayûm was determined
or influenced by fault lines; an extended examination of the cliffs
however gave negative results, with one exception; the long narrow
hill-mass to the north east of Gar el Gahannem is bounded by faults
on both sides and that on the west can be easily traced for seven or
eight kilometres northwards, and throughout its length its influence
on the topography is very conspicuous.
[Footnote 26: BEADNELL. _The Fayûm depression: A Preliminary Notice
of the Geology of a District in Egypt containing a new Palaeogene
Vertebrate Fauna_. Geol. Mag. Dec. IV, Vol. VIII, No. 450, Dec. 1901,
p. 540.]
[Footnote 27: See reports on Kharga Oasis (1900), Farafra Oasis
(1901), Dakhla Oasis (1901), and Baharia Oasis (1903), issued by
Survey Dept. P.W.M., Cairo.]
[Footnote 28: Public Works Ministry Report. Cairo, 1899.]
[Footnote 29: BLANCKENHORN. _Geologie Aegyptens_, Berlin 1901, Pt. IV,
pp. 339-344.]
[Footnote 30: „ p. 341, Fig. 10. Skizze der Strukturlinien des
Fayûm.]
[Footnote 31: „ Taf. XIV. Querprofil durch den Fayûmgraben.]
[Footnote 32: BLANCKENHORN, _Neue geologisch-stratigraphische
Beobachtungen in Aegypten_, S.-Ber. d. math.-phys. Classe
d. kgl. bayer. Ac. d. Wiss. Bd. XXXII 1902, Heft III, München 1902,
pp. 428, 429.]
PART III.
=GEOLOGY.=
* * * * *