We have presumed that in Miocene times the Fayûm remained land, no
traces of deposits of that age having been recorded; possibly the area
underwent considerable denudation during the Miocene and early Pliocene
periods, but of this it is difficult to adduce definite evidence. The
records of Pliocene times in the Fayûm may be classed as follows:—
(J). _Marine deposits_ of Middle Pliocene age.
(K). _Borings_ on rock surfaces, exact age doubtful.
(L). _Gravel Terraces_, probably late Pliocene. } (or early
} Pleistocene).
(M). _Gypseous Deposits_, probably latest Pliocene. }
_J._—=Marine Deposits: Middle Pliocene.=
In Middle Pliocene times the area, which had probably undergone
considerable denudation, was again invaded by the sea, and we find
at Sidmant el Jebel, on the south-east side, definite evidence of
deposits of this age in the shape of sands containing such well known
forms as _Ostrea cucullata_ and _Pecten benedictus_.
The beds in question reach an altitude of from 60 to 70 metres and
were first brought to notice by Schweinfurth. Although they are in
reality on the Nile Valley side of the separating ridge or saddle,
there is little doubt that the same beds will, when looked for, be
found within the Fayûm depression in places where they have been
preserved. As has already been mentioned this south-eastern side of
the Fayûm yet remains to be examined and mapped in detail, and the
determination of the relation of these marine sands to the gravel
terraces shortly to be described is a matter of primary importance
for the proper interpretation of their relative ages.
_K._—=Borings on Rock surfaces; of doubtful age.=
There are within the Fayûm depression numerous rock-surfaces pierced
by borings, apparently the work of marine boring mollusca but naturally
offering no exact evidence as to their age and origin. These borings
are found at two distinct levels, approximately from zero to 20 metres
above sea-level, and at 112 metres above sea-level.
(α) _Low level borings._
Between Tamia and Dimê, near the eastern end of the Birket el Qurûn,
the lowest ground, consisting of poor sandy land with tamarisk scrub,
bordering the lake and cultivation, is bounded by a low escarpment
of beds of the Birket el Qurûn series. Along certain horizons one
or more beds of calcareous sandstone weather into large globular
masses, which as already pointed out are in reality huge concretions,
but which may have been further rounded by water-action. The chief
point is, however, the fact that these blocks are honey-combed in the
most remarkable way by beautiful examples of borings; their presence
was first noticed by Schweinfurth. The globular masses of sandstone,
often several feet in diameter, are worn on the surface into a number
of parallel ledges, each of which is perforated with countless numbers
of vertical holes, averaging 10 millimetres in diameter (maximum 15
millimetres), placed at right angles to the ledges; these holes are
not, as a rule, connected from one ledge to another. They occur in
every stage of perfection, from hollows as small as the finger tips
and only a few millimetres deep, to long completed chambers which
generally show considerable tapering, and are often placed so close
together that the dividing wall is pierced.
Fig. 7 and Plate XIII show the appearance of these bored rocks.
[Illustration: FIG. 7.—Block of sandstone pierced by numerous
borings.]
At El Kenîsa, a promontory jutting out into the lake, sandstones
showing shell-borings occur at a height of 14 metres above
sea-level. Between Dimê and the lake a calcareous sandstone contains
many borings, 66 metres above the lake-level, or about 22 metres
above sea-level.
[Illustration: PLATE XIII.
BORINGS IN FALSE-BEDDED SANDSTONE, TWO KILOMETRES SOUTH OF DIMÊ.]
(β) _High level borings._
Further west, but at a considerably higher level, borings are again
met with. In this case a hard compact limestone, forming a dip-slope
surface on the top of the lower cliff of the Qasr el Sagha series,
was found pierced with borings, similar in character to those of the
lower level. The exact locality where these high level borings were
observed is 14 kilometres west of the western end of the lake and 16
kilometres north-east of the eastern extremity of Gar el Gehannem. The
height was determined as 156 metres above the Birket el Qurûn,
or 112 metres above sea-level, and we have every reason to believe
these figures to be approximately correct. Up to the present time
borings at this altitude have not been met with in any other locality.
At first sight it seems surprising that the occurrences should be so
limited, but it should be remembered that only in those cases where
borings were made in the very hardest and most durable rocks could
they have been preserved to the present time. Considering the amount
of denudation which has taken place in the area since the Pliocene
period it is surprising that any of the rocks which formed the actual
surface of the country at that date should still be preserved; and
in all probability the comparatively few records that exist to-day
owe their preservation to the protection afforded by superficial
deposits. Under the present rigorous desert conditions, when the whole
surface is subjected to continual and rapid changes of temperature,
and every exposed rock is being worn down by the natural sandblast,
it must be admitted that in a comparatively short time every trace
of the borings now exposed will have been removed. At the same time
the denudation of superficial deposits will probably lay bare other
bored rock-surfaces, and the conserving nature of drift sand itself
where accumulated to even a limited degree must not be forgotten.
_L._—=Gravel Terraces: ? Upper Pliocene.=
On the north, east, and south-east sides of the Fayûm, well marked
terraces of gravel are found at certain levels up to a maximum of
about 170-180 metres above sea-level. Nine kilometres east of Sêla
the summit of the ridge separating the Fayûm and the Nile Valley is
formed of thick deposits of gravel, laid irregularly and unconformably
on the top of limestones belonging to the Birket el Qurûn series. The
lowest terrace occurs only 15 metres above the canal[86] running
along the outside of the cultivation. The main deposit of gravel is
laid on the top of the limestones and marls at 70 metres above the
canal; it is some 50 metres thick (summit 120 metres above canal)
and consists of a mass of well-rolled flint and quartz pebbles, with
blocks of limestone (frequently full of well-known Eocene fossils
such as _Carolia placunoides_). Large well rounded blocks of grey
quartzite and pebbles of black quartzite also occur, besides rounded
blocks of silicified wood. A certain amount of false-bedding occurs
and false-bedded sand was noticed in places. Numerous derived rolled
fossils are present, but no contemporaneous remains were found. On
the summit of the ridge is situated the remnant of an old pyramid-like
building.
Fig. 8 shows the relation of these gravels to the underlying rocks.
[Illustration: FIG. 8.—_Sketch showing relations of Middle Eocene
to Pliocene Gravel Terraces on the east side of the Fayûm._
_Birket el Qurun series._—(_a_) Clays, marls and limestone;
(_b_) Limestones with _Operculina_ (_O. discoidea?_). Pliocene
(to Pleistocene); (_c_) Coarse deposits of gravel, etc., with huge
blocks of derived Eocene limestone with _Carolia_, etc.; (_d_) sands
and sandrock with leaves of hard sandstone; (_e_) sand, gravel and
conglomerate.]
At the spur of the cliff immediately to the east the terrace is
laid on to limestones of the Birket el Qurûn series at a height of
32 metres above the canal. Enormous blocks of _Carolia_-limestone,
some exceeding 3 × 2 × 1·5 metres in measurement, are included in
this deposit; such blocks cannot have been transported far, and were
doubtless derived from formerly-existing higher beds in the immediate
neighbourhood. The matrix of the deposit is usually crushed limestone
with sand and gravel. Occasional fragments of silicified wood (and
further west large logs), evidently derived from the Fluvio-marine
beds, also occur.
In favoured localities the relation of the gravels to the Eocene is
still better seen; the lower beds of the terrace here are sometimes
formed of sands and sandy beds dipping 10° eastward.
At the little promontory 9 kilometres east of Sersena the same deposits
reach an altitude of 157 metres above the canal below.
Further north another cake of gravel caps the summit, attaining
here 60-70 metres above the canal-level. Probably these deposits
were originally more or less connected and continuous, but since
their deposition denudation must have removed the greater part, as
they are now only found here and there capping the highest points
of the escarpment along the east side of the Fayûm. Such isolated
gravel-capped hills occur notably 12 kilometres east of Roda, 16½
kilometres east and 17½ kilometres north-east of Tamia.
Along the north side of the Fayûm the same deposits are found,
in some cases covering large areas.
Twenty-five kilometres N.N.E. of Tamia the Eocene beds, here an
alternating series of clays and limestones, are capped by a deposit
consisting of coarse rolled gravel, with blocks of silicified wood
enclosed in a sandy gypseous base, some 10 metres thick. A larger
and similar deposit caps the next high ground four kilometres to the
west, and about 9 kilometres N.N.E. of Garat el Faras; in this case
it forms a round-topped gravelly hill-range, attaining a height of
about 165 metres above the canal to the south-east. The loose gravel
at many points passes into hard conglomerate, notably in the hills
9 kilometres east and 4 kilometres north-east of Garat el Gindi. At
the former spot the conglomerate is composed of blocks of limestone,
with round pebbles of flint and quartz, sandstone and quartzite,
and fragments of silicified wood, cemented by sand and calcareous
material. Blocks of silicified wood also occur strewn on the surface
of these gravel deposits.
In the hills north-east of Garat el Gindi the gravel deposits do not
occupy the summit of the escarpment but occur laid on to a platform of
beds belonging to the Qasr el Sagha series. Behind, another escarpment,
that of the Fluvio-marine series, rises to the plateau summit.
Fig. 9 will show the general relation of the different formations in
this part of the district.
Near Elwat Hialla the deposits contain numerous blocks of basalt
in addition to the usual constituents. The basalt is derived from
the sheets interbedded at the base of the Oligocene a little to the
north. As these gravels are here close to that formation, blocks of
sandstone, basalt, and silicified wood now form a large proportion
of the constituents.
Along the north side of the Fayûm depression, to the west of Elwat
Hialla, the gravel terraces are almost absent, having been removed
nearly completely by denudation. That the terraces once existed
throughout this region is however shown by the small patches met with
to the north-east of Widan el Faras, the eastern extremity of Jebel
el Qatrani, and at several points high up on the escarpments as far
west as the western end of the lake. Beyond the latter point these
terrace gravels have not been noticed; the slopes of the depression
become more and more obscured by loose superficial flints washed down
from the plateau, and the existence of underlying terrace gravels
could only be shown by detailed mapping.
[Illustration:
PLIOCENE (TO PLEISTOCENE) —1. Terrace of gravel and conglomerate.
UPPER EOCENE-OLIGOCENE —2. Sands and sandstones.
MIDDLE EOCENE —3. Clays, marls and limestones of the
Upper Mokattam.
FIG. 9.—Sketch-Section through summit of Fayûm Escarpment at
Elwat Hialla.]
Near Widan el Faras the terrace occurs at a level of about 220
metres above the Birket el Qurûn, or 175 metres above sea-level,
and consists of a 10-metre thickness of a semi-consolidated mass of
boulders and pebbles of sandstone, limestone, and basalt, with fine
gravel and sand, unconformably laid on to the variegated sandstones
of the Fluvio-marine series.
In the neighbourhood of the Survey’s main excavations for fossil
bones, to the north of Garat el Esh, several local remnants of the
formerly more or less continuous gravel terrace were detected[87]. The
height was probably more accurately determined here than elsewhere
and the upper limit of the deposits was found to lie at approximately
170 metres above sea-level; this figure may indeed be taken as the
average height of the Pliocene terraces throughout the Fayûm.
[Illustration: PLATE XIV.
PLEISTOCENE LACUSTRINE CLAYS WITH TAMARISK STUMPS IN SITU AT 50 METRES
ABOVE PRESENT SURFACE OF THE BIRKET EL QURUN.]
Briefly then we have shown the existence of the well marked remains
of a gravel terrace 170-180 metres above sea-level, throughout the
south-east, east, and north sides of the Fayûm depression, and the
first question that suggests itself with regard to these deposits
is, whether they are of marine or of freshwater origin? From their
position in part capping and in part perched on the flanks of the
escarpments, it is evident that the depression of the Fayûm must
have been partly formed before their deposition; probably it had
approximately obtained to its present form and dimensions, except as
to depth. The terrace certainly marks the shoreline of the sheet of
water in which its constituents were deposited, and the surface of this
water must have attained a height of nearly 200 metres above present
sea-level. It is not unlikely that some of the extensive plains of the
Fayûm may owe their existence in part to the presence in Pliocene
times of the sea or of a large inland lake, that they may in fact
be plains of denudation. The plain above the escarpment of the Qasr
el Sagha series, lying between 150 and 200 metres above sea-level,
and stretching throughout a large part of the north of the Fayûm,
has characters which tend to support this idea.
Unfortunately the gravels are entirely barren of contemporaneous
organic remains, with one exception; near Ez. Qalamsha some examples
of _Ostrea cucullata_ were discovered, and these we believe to
have truly belonged to the lower beds of the terraces and not to
have been derived from the undoubted marine Middle Pliocene beds
of Sidmant. If the existence of _O. cucullata_ in these terraces
could be confirmed we should undoubtedly class them as marine and of
Middle Pliocene age. But the single evidence of the Qalamsha shells
is not sufficient, and confirmatory occurrences must be obtained and,
if possible, the relation of the terraces to Schweinfurth’s marine
Sidmant beds determined, which has not been yet done.
_M._—=Gypseous deposits, probably dating from the close of the
Pliocene Period.=
Of distinctly later date than the gravel-terraces are the widely
distributed gypseous deposits of the Fayûm and Nile Valley. These
deposits are found covering the plain which separates the Nile Valley
cultivation from the Fayûm depression, gradually rising from the
level of the former until they overlie the gravels capping the summit
overlooking the Fayûm (Section XXI).
Near the Pyramid of Medum the following beds are seen at the edge of
the desert plain:—
_Top._ Metres.
Pure, gravelly, or marly gypsum 1-2
Clayey shales with gypsum and salt 1-1½
White marly limestone with much salt } probable {
and fish-remains (fish-scales, etc.) } part of { 2
} Ravine beds. {
Yellow sandstone with fish-scales, etc. } { 3
The gravel deposits along the east side of the Fayûm are always capped
by a gypseous bed. The latter is often 2 metres thick and frequently
occurs as solid and almost pure white crystalline gypsum; sometimes
it is calcareous and is frequently deposited in a tufaceous manner,
especially resembling a tufa on the weathered surface. At other times
it passes into a yellowish compact mass and may be very saliferous.
Frequently the deposit is full of rounded pebbles, the latter
being often in the greater proportion and forming a sort of
gypsum-cemented conglomerate. Not unfrequently it is impossible to
draw any divisional line between the terrace gravels and the gypseous
gravels above. Probably they are both closely connected and of Upper
Pliocene age.
_N._—=Summary of the Pliocene Period.=
From the above descriptions it is probable that the Pliocene period
is represented in the Fayûm by the following:—
(1) Marine beds of Sidmant, undoubtedly of Middle Pliocene age and
reaching a level of from 60 to 70 metres above present sea-level.
(2) Borings on exposed rock-surfaces at two distinct levels, the
lower 0-20 metres, the higher some 112 metres, above sea-level. These
borings appear to be the work of marine boring mollusca, and although
those on the lower level may perhaps be of Middle Pliocene age with
the Sidmant beds, the similar examples discovered at a much higher
altitude (112 metres), point to the sea having attained a much higher
level in later, perhaps Upper Pliocene, times.
(3) An extensive beach or terrace of gravel on the south-east, east,
and north sides of the Fayûm, attaining a maximum level of about
170 to 180 metres above sea-level.
All the known facts seem to be satisfied if we imagine that in
the Middle Pliocene the sea occupied the area, depression probably
continuing until the 112 metre level with the highest borings was
reached. Perhaps the lowest part of the terraces was formed during
this time. In the later Pliocene times we may infer that the area
was occupied, up to 180 metres above present sea-level, by a vast
inland lake, perhaps of brackish water, connected with the sea on
the one hand and the fiord or lakes of the Nile Valley on the other,
the deposits of which have been described elsewhere[88].
Along the margins of this gigantic lake, these great accumulations
of gravel might well have been formed, chiefly of material derived
from the immediate shores, augmented perhaps by a certain amount of
sediment brought by river-currents from the south.
Finally, from the way in which the gypsum and gypseous deposits are
laid on the terrace gravels, and from their extension and thickness,
we may presume that they were deposited on the bottom of just such
a lake on evaporation of its water, when the sulphate of lime in
solution, becoming more and more concentrated, may have been finally
precipitated.[89]