From an examination of the series in the field, there is no doubt that, in at least the centre of the area, the deposition of the lowest beds was continuous with those of the Qasr el Sagha (Middle Eocene) series below. Followed away from the centre (i.e. the district round Widan el Faras, the eastern extremity of Jebel el Qatrani) the series gradually thins out, and eastwards, at Elwat Hialla, some 23 kilometres north of Tamia, has a thickness of only 40 metres, the basal beds being apparently laid on to a bed of limestone of the Qasr el Sagha series about the horizon of Bed 12 in [Section XXIII.] The junction here is apparently one of perfect conformity as far as the individual beds go, and the peculiar sequence does not seem to be due to ordinary overlap; it appears as if the change from marine to estuarine conditions had set in earlier here than further to the west, with the result that the upper Qasr el Sagha beds are wanting. Moreover, the accumulation of estuarine beds went on so slowly in this locality that the series does not attain to nearly its normal thickness, while further east it dies out altogether. The slight dip to the north is identical in both series, their lithological characters being, however, very different.

Although the Qasr el Sagha series contains numerous bands of clay and sandstone, the continual recurrence of thick beds of limestone at once gives it a distinguishing feature from the group under discussion; the latter is in fact characterized by the highly-coloured sandy, and to less extent clayey, character of its beds. While the Middle Eocene is essentially marine, the succeeding formation marks the retreat of the sea and the incoming of estuarine and brackish water conditions.

Before discussing the age of the Fluvio-marine series it will be well to describe its development in the field. The beds of the complex are throughout the district always found following on above the Qasr el Sagha beds, although their thickness varies considerably, as might be expected in a series of this nature. The most easterly locality to which the formation was mapped is the scarp 23 kilometres due north of Tamia, known as Elwat Hialla. Here the beds form a separate escarpment, consisting of only about 40 metres of sands and sandstone grit (sometimes silicified) with pieces of silicified wood: some of the beds of sandstone have a concretionary stem-like weathering. From this point these beds extend westwards far beyond the western end of the lake, always forming the highest escarpments of the Fayûm depression. A kilometre or two from our most easterly point the first basalt sheets are seen, and these, preserving the same level as far as can be observed, continue some 60 kilometres further west, to a point nearly due north of the western end of the Birket el Qurûn. The series, only 40 metres thick at the eastern end, gradually thickens as it is followed westward, until it reaches its maximum development in the cliffs of Jebel el Qatrani, north-west of the temple of Qasr el Sagha, where a thickness of some 210 metres is attained.

Just 29 kilometres N.N.E. of Tamia (6 kilometres N.W. of the prominent western scarp of Elwat Hialla), a long hill offers a good section of these beds, which consist of a variegated group of green sands, red clays, coarse sandstones, red and yellow sand and sandstone, etc., capped by a band of hard impure yellowish limestone with numerous enclosed sand-grains (calcareous grit). Near the same place is an interbedded sheet of basalt, which is sometimes followed by another band of impure limestone and the latter by false-bedded sandstone. Huge logs of weathered-out silicified trees are seen strewn about.

The following is a detailed section of the series, measured from a point 3½ kilometres W.N.W. of Elwat Hialla, and about 28 kilometres N.N.W. of Tamia, to the top of the escarpment 4 kilometres further north:—

Undulating sandy, gravel-covereddesert[66] stretching northwards.
Top of escarpment.Metres.
1.False-bedded sandstones8
2.Band of impure limestone
3.Interbedded basalt sheet
4.Sandstone
(Section continued in hill ¾kilometre further north-east).
5.Hard yellow limestone with enclosedsand-grains; cavities full of calcite1
6.Greenish-white sand-rock1
7.Hard reddish-brown stem-weatheringsandstone1½
8.Greenish or white sand and sand-rock3
9.Variegated sandy clays; sand-rock withoccasional fragments of bone6
10.White sand-rock1
11.Rose-coloured sandstone2
12.Hard grey white marly clays2½
13.Coarse yellow sandstone5
14.Reddish, white, and variegated sands andsand-rock8
15.Grey, reddish and yellowish clays, withbands full of plant-remains3½
16.Brown clayey, sandstone2
17.Greenish sandstone1
18.Sandy grey clay1½
19.Hard grey sandstone½
20.Greenish sand-rock and clayeysandstone3
21.Dark red clay1
22.Sands, etc.; outcrop of bed covered withsilicified trees of large dimensions, 12-15 metres long10
23.Clays with hard grey false-beddedsandstone and showing fine mammilary weathering at top. Silicifiedlogs on surface8
24.Red clays, sandy clays and argillaceoussands4
25.Reddish sand-rock1
26.Yellowish sand-rock, in partfalse-bedded2
27.Red clays with thin sandy bands1½
28.Coarse grey sandstone2
29.Red and green sandy clays with thin bandof hard white sandstone at top1
30.Bright red clay4
31.Red clays with thin green sandybands3
32.Greenish sand-rock with thin red clayeybands1
33.Reddish white mottled clayey sandstonespassing up into red and white mottled clays and sandy clays8
34.Fine white sand3
35.Black ferruginous silicifiedsandstone
Total thickness90
Base.
Junction with Middle Eocene (Qasrel Sagha series).

Plate X.

EL QATRANI RANGE FROM THE SOUTH-EAST.

A little further west, at a point 25 kilometres north of the eastern end of the Birket el Qurûn, thick beds of white coarse sandstone form the upper part of the escarpment. Below comes a bed of yellowish impure limestone and below this an interbedded sheet of basalt 21 metres thick, underlaid by more white sandstone.