Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/109

 reduced copper-ore in the clay. The inhabitants were, however, not entirely without metal, as a small bracelet of copper was found in a tomb, the only one remaining unopened, in Wady Sidreh, associated with lance- and arrow-heads of flint, and a necklace of beads formed of spiral marine shells bored through for stringing.

Alluvium of Ghenneh.—The alluvial deposits of the Ghenneh valleys have certain features of interest in connexion with the ancient mines. The downland at the foot of the granitic escarpment is covered with a gravel made up of pebbles of red, yellow, and white quartz, and brown sand from the waste of the Triassic sandstones; a few pieces of fossil wood were also found. The watercourses are bounded by steep and terraced cliffs, mainly of granitic detritus, of a coarse but comparatively uniform grain ($1⁄4$ inch); but in the central valley these are bordered at lower levels by a coarser gravel, with good-sized boulders, probably indicating the return of a more rapidly flowing stream in later times.

In the finer alluvium a single but unbroken shell of a large freshwater bivalve was found, which, on comparison, proves to be identical with the large Anodon-like form, Spatha Chaziana (Lea), now living in the Nile. Broken fragments of the same shell were also found in the mine, accompanying the stone and wooden tools already mentioned, and apparently having been carried in by the miners for food. These latter are well preserved, the nacre of the interior being fresh and brilliant; but the shell from the gravel is rough and white, having lost all trace of its original polish and colour. Unless, therefore, we suppose that these shells have been brought from the Nile, which is not very likely, as the distance is about 300 miles, we must admit that, in the days of the old miners, the Ghenneh plain and valleys were sufficiently well watered to allow of large fluviatile mollusca living in them. But even supposing the shells to have been imported, the inference is that a great part of the gravels have been deposited, and fresh channels cut through them, in the last 4000 years.

Alluvium of Wady Ferran &c.—The evidence, however, of the existence of lakes or slow-flowing rivers in Arabia Petræca is not confined to the somewhat doubtful case given above. In the upper part of Wady Ferran and the higher valley of Wady el Scheick, which are cut through a comparatively soft grey granitic gneiss, there are considerable accumulations of fine-grained well-stratified alluvium, forming terraced masses which, although much eroded by subsequent action of the weather, often attain a height of from 40 to 60 feet above the bottom of the valley. They have been attributed by a recent traveller to the action of glaciers, and described as moraines; but a close inspection proves them to be only ordinary lake- or river-alluvium, as in places they are full of calcareous nodules (race or kunkur), and also contain beds of calcareous tufa (incrusting the stems of carices or plants of a similar character), as well as freshwater shells, including Lymnoea truncatula and a species of Pisidium,