SHRINE AT AKARAQ
The cliff of Tiggedi, with its continuation eastward for some way beyond the Eghalgawen hills, is the southern shore of a wide valley which serves as a catchment for all the waters of Southern Air that do not escape by the south-east corner of the plateau into the Azawagh valleys previously described. The cliff is a geological phenomenon of great interest. At the point where the Abellama road descends into the valley some forty miles south of Agades the cliff is sheer for a height of over 200 feet. The path down from the general level of the desert to the dry alluvial plain, which forms the bottom of the River of Agades, is steep and rough. Standing at the top and looking east and west, it seems like a cliff on the sea-shore broken by capes and small inlets; the illusion of maritime action is remarkable. Westwards at Marandet, though still a definite feature of the area, it is less abrupt; erosion has broken down the precipice, while the Marandet torrent has eaten away a ravine leading even more gradually up to the level of the desert. Eastwards, on the other hand, the cliff continues unbroken as far as the Eghalgawen and T’in Wana massif, where higher hills above the desert level take the place of the cliff itself. Though they form a salient in the line, their abrupt northern slopes continue the eastward trend until they come to an end near Akaraq, where the cliff reappears. Here again it is absolutely sheer, if somewhat less elevated; it is broken by a narrow inlet where the Akaraq valley, the only tributary[72] of any size on the south bank of the River of Agades, enters the main basin. At this point the cliff assumes the most fantastic form. The sandstone has been shaped by erosion into pinnacles and blocks of the strangest shapes. The Akaraq valley itself runs back like a cove in a cliffbound sea-coast; both banks are nearly vertical, decreasing in height as the level of the bottom gradually rises to the desert, where the bare rock has been deeply cut into by the water, lying in a semi-permanent pool in a very narrow gully. The bottom of the inlet is covered with luxuriant pasture and some fair-sized trees, while at the mouth, in the main valley, stands an island of rock with vertical sides to complete the illusion of a sea-coast.[73] From the top of the cliff you may look across the great broad valley toward the mountains of Air that are scarcely visible in the north. No defined bank appears to limit the far slope of the basin. There is deep green Alwat pasture[74] in the nearer distance, merging imperceptibly into yellow grass and bare sand further away. The blazing glare and shimmering heat wash the feet of the cliff where a shelving beach of loose white sand has been thrown up against the rocks. The plateau at the top of the cliff is quite flat, and covered with a layer of small hard gravel over the rock. It is without any vegetation.
The great valley bears several names. At the Akaraq inlet it is called Tezorigi. Opposite the Eghalgawen massif it is the T’in Dawin, and further west the Araten valley. West again it has no name, but where it finally leaves the mountains of Air for the Assawas swamp on the way to the T’immersoi basin, the natives call it the Ighazar n’Agades, or River of Agades, from the city which stands on its northern shore, and this is the name I have adopted for the whole. How far the cliffs extend eastward I do not know. A great fork in the valley is visible from Akaraq, the channel is divided by a bluff promontory, but the cliff continues along the southern bank of the southern branch until it is lost from sight. The ridge of Abadarjan which Barth crossed north of Tergulawen, I expect, is part of the same formation.
PLATE 7
RIVER OF AGADES LOOKING SOUTH FROM TEBEHIC IN THE EGHALGAWEN MASSIF
EGHALGAWEN MASSIF FROM AZAWAGH
Maritime action is highly improbable as the origin of the cliff. No traces of shells or beaches at different levels, to be accounted for by a receding sea, have been noticed. The supposition that all the Sahara was once a sea-bed is untenable, and in any case maritime action would hardly be limited to a few small areas such as this one. It seems easier to look for another explanation. The cliff and the Eghalgawen massif are a sandstone formation, but the Taruaji mountains of Air opposite the little Eghalgawen-T’in Wana massif are granitic. The cliff represents, I hazard, a fault north of which the igneous formation of the Air plateau has been extruded. The ground to the south slopes gradually away from the edge of the cliff, accounting for the virtual absence of any tributaries on the left bank of the River of Agades. There is apparently no igneous rock south of the basin, there is very little else to the north of it, with the exception of some Archean and very early rock. The fault, occasioned by the volcanic action which formed the massif of Central Air, erected a barrier to the southward drainage of the mountains, and the waters of Southern Air were diverted westward. A larger rainfall than now caused the gradual silting up of the area between the bottom of the fault and the southern part of the mountains. As the ground level rose and became an alluvial plain from which practically only Mount Gadé and the island off Akaraq emerge, the rain floods began to wash along the cliff and eroded the sandstone into the fantastic forms which are now seen. Wind-borne sand from the eastern desert completed the process of shaping the rocks. The accretion of alluvium diminished with a decreasing rainfall in Air, and the surface deposit of wind-borne sand formed what is now in dry weather a hard gravel-covered plain which, in the rainy season, turns into mud-flats and becomes almost impassable. The water flows aimlessly in the alluvium along deep-cut gullies with vertical sides that constantly change their course. The alluvial origin of the plain of the River of Agades is unmistakable.