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 andfish-remains (fish-scales, etc.) | probable part of Ravinebeds. | 2 | |||
| 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.