Beyond the Bahr the desert is formed of a hard limestone much cut up by the action of wind-borne sand as already mentioned. This limestone is very unfossiliferous, occasional obscure nummulites seen on fractured or smooth surfaces being the only indications of its Eocene age.
The conical-peaked hills of Gar el Hamra on the left of the road at 151 kilometres were so striking that a detour was made specially to examine them. They were found to be composed of black ferruginous silicified sandstone or quartzite at top, with false-bedded sandstones below. They overlie nummulitic limestones forming the surrounding plain, and are not improbable Post Eocene lacustrine deposits, similar to those within Baharia Oasis (see [pp. 60-62]).
From here onwards up to the oasis-depression the plateau consists of hard brown limestone, more or less silicified, and contains nummulites and oysters. The Eocene strata, thus extend right up to the escarpment of the depression on the north side of the oasis. The geological structure within the depression will be found discussed in [Chapter V].
Road from Minia to Baharia.Road from Minia to Baharia.—The cultivated land extends for some 9 or 10 kilometres west of Minia town, and at the time of the Survey expedition (early in October, 1897) this area was mostly covered by flood-water. Boats were therefore taken to the edge of the desert, and the march west was commenced from Nasl Nadiub Lengat, a small village on the cultivation-limit in lat. 28° 6′ 24″, long. 30° 39′ 45″ E., bearing from Minia railway station 9° north of west, distance very nearly 10 kilometres. The road westward being ill-defined, and the party knowing that any course followed a little north of west would surely lead to the oasis, no attempt was made to follow the track precisely, the course being rather chosen to take advantage of commanding points so as to map as much topography as possible en route. As will be seen further on, however, the road was struck some distance before reaching the oasis, and was thence followed to Zubbo.
On leaving Nasl Nadiub Lengat the course first taken was about 32° north of west. The desert here rises very gradually from the flood-level, (i.e. about 40 metres above sea-level), there being no cliff bounding the Nile Valley on the West at this point. For about 6 kilometres the ground was sandy, with occasional patches of flood-water and some grass; then came a stretch of level gravelly ground, and at 11½ kilometres some low sand-dunes were crossed. The course was now changed to about 3° south of west, and at 14 kilometres a descent was made from the gravel-plain into a limestone-depression, with gravel-capped eminences on either side. At 22 kilometres the gravel-strewn plain was again come on, a few low mounds, also gravelly, being passed at 31 kilometres, and camel-tracks, doubtless part of the Minia-Baharia road, being noticed coincident with the survey line at 37 kilometres. Continuing following these tracks, another camel-road was found to branch off at 46 kilometres to the north-west. The march was continued along the same track going a little more south of west, over a monotonous gravelly plain, with limestone showing through it in small patches, till at 78 kilometres from Nasl Nadiub Lengat a conspicuous though small mass of fissile gritty limestone was come on, which afforded a good survey-station. North and west of this are low gravel-covered hills. Turning a little north of west, a large extent of low table-like hills was seen on the south. At about 90 kilometres low plateaux of limestone, capped by gravel, closed in so as to form a defile about a kilometre wide, through which the line of survey passed, and at 98 kilometres a large sandy and gravelly depression, bounded by limestone scarps and containing numerous large limestone hills, was entered. Within the depression the course followed was about 30° north of west, so as to map roughly the escarpments on either hand. About 10 kilometres from the point where the depression is entered a long stretch of heavy sand was crossed beyond which tracks going west were come on, and the edge of the limestone plateau on the left curved round so as to cross the road. Ascending this low scarp at 116 kilometres, the course lay over white limestone, with sharp angular flints on its surface, and low limestone hills on either side. At 124 kilometres the broad belt of sand-dunes, the Abu Moharik, was reached. The dunes, which are of considerable height, run nearly north and south, and have a total width of some 4 kilometres; they formed the most serious obstacle of the entire journey. Beyond the dunes is a hard limestone plain, crossed by a low ridge (forming part of a higher plateau) at 136 kilometres. Beyond this ridge are low limestone-hills on either side, the floor being generally of hard white limestone. At 151 kilometres an oval depression in the limestone plateau, with its longer axis (about 4 kilometres) running W.N.W., was entered; this depression is full of hills of white chalk, which also forms the floor here. Ascending the opposite scarp of the depression at 159 kilometres, a narrow strip of higher plateau of much harder limestone was crossed, the edge of the scarp of the oasis of Baharia being reached at 160 kilometres, after marching for 57 hours from Nasl Nadiub Lengat. Up to this point there had been a gradual rise of the ground, from 40 metres at the Nile Valley to 265 metres above sea-level at the edge of the oasis.
The descent into the oasis is not difficult, the scarp being sandy and the fall gradual. At about 4 kilometres W.N.W. from the edge of the scarp is the first well or spring of the oasis, Ain Gelid (lat. 28° 19′ 28″ N., long. 29° 8′ 40″ E. of Greenwich), a small pool surrounded by grasses and with a tree growing near it. The barometric observations gave for this point the level 134 metres above sea, so that the total drop from the edge of the scarp is about 130 metres. From Ain Gelid the village of Zubbo bears about 15° north of west, and is some 17 kilometres distant, but owing to the hills between the two places necessitating a slight detour, the actual distance to be traversed is a few kilometres greater.
Geology of the Minia-Baharia Road.The road from Minia to Baharia shows essentially the same geological features as the one from Maghagha already described. The gravel which strews so large a portion of the road to the east is mainly composed of quartzite and flint pebbles, of a prevailing brown colour. Some of the rounded flints show a concentric structure, and are evidently segregation-nodules derived from chalk-beds; a very fine specimen of these, measuring some 20 c.m. in diameter, of almost perfectly spheroidal form, was obtained. The gravelly covering is frequently very thin, the limestones underlying it showing through in numerous places. No evidences of the precise age of this gravel have come to the authors’ knowledge, but it is certainly Post-Eocene. It appears to be the same formation which is found covering the edge of the plateau west of Girga[24] and south of Assuan (east bank) and at various other points of the Nile Valley. It overlies beds of every age from the Nubian Sandstone to the Lower Mokattam.
The limestones which underlie the gravel near the Nile, and which are well exposed in the depression crossed 14 kilometres from the edge of the cultivation, are crowded with nummulites of various species, N. gizehensis and N. curvispira being specially common; these rocks belong therefore to the Lower Mokattam Series (Middle Eocene).
The limestone underlying the gravel further west (from about 30 to 80 kilometres west of the cultivation-limit) is only seen in small patches; it varies in character, being in some places loose and tufaceous in texture, and in others gritty and fissile, passing into a calcareous grit. The mass of gritty limestone at 78 kilometres, noted above, is about 6 metres in length by 2 metres high and broad; it shows a peculiar stalagmitic structure, the layers always parallel to the free surface. Several smaller masses found around all show a similar structure, and where the rock is exposed on the floor concentric fissuring is frequently seen. The sand which strews the surface here is largely calcareous, being doubtless in part derived from the gritty limestones.
The eastern part of the low hills lying to the left of the track at about 85 kilometres from the cultivation-limit show the following section (total height about 13 metres):—