Page:Africa by Élisée Reclus, Volume 2.djvu/106

 84 NOETH-WEST AFEICA. forbidding aspect, but for the green fringe of palms partly concealing the town, and pleasantly contrasting with the surrounding yellow plain, furrowed here and there with grey or reddish strips. The powdery soil, in which the camel sinks at every step, is strewn with blocks of sulphate of lime, occasionally forming poly- hedric groups, which are intersjjersed with gypsum and quartzose sand iu nearly equal proportions. In the midst of the plain stand the so-called gitrs or kefs, isolated eminences 130 to 160 feet high, and terminating in a table of white chalk, the remains of an upper layer which formerly covered the whole district, but which has been gradually eroded by the ceaseless action of outward and subter- ranean physical agents. It is easy to detect the work of destruction still going on. The superimposed strata of sandstone, carbonate of lime, gypsum, marl, or clay, resist in different degrees the influence of heat and cold, which oscillate between such great extremes in these solitudes ; hence follow irregular movements of expansion and contraction, producing faults in the strata. Water also infiltrating through the porous soil expands and disintegrates certain rocks, the upward pressure causing fractures in the surface layers. Throughout the whole of the Ghadames plateau this action is evident. The ground is covered with small cones upheaved by the thrust of underlying forma- tions ; between these irregular eminences rising in fantastic disorder above the normal level are still visible the uniformly superimposed strata ; the rocks present the most varied aspects, from the solid and compact strata to one of the most complete disintegration. Certain hills still preserving their upper table have been fissured on one side, like burst flour-bags discharging through the rent a stream of sand from the inner rocks, which have been gradually triturated by the alternating temperature. Thus the plateau, at first cut up into isolated eminences, is being transformed into a system of dunes, some of which remain for ages disposed round a more solid central core, whilst in others the rock becomes completely ground to dust, drifting under the action of the winds and merging in the lines of dunes, whose long undulations cover certain parts of the desert. The rocks which best resist those weathering influences are the ferruginous sandstone deposits ; hence in many places the surface, already denuded of the limestone and gypsum formations, is still covered with hard and blackish sandstone masses, which yield a metallic sound under the wayfarer's footsteps. The Ghadames oasis is encircle^ by an earthen rampart 3 J miles in circum- ference, formerly raised against the marauding tribes of tlie desert, but now possessing no defensive value. Broken here and there by broad gaps at some points, especially on the west side, it serves to accumulate the sands, which are thence blown by the winds into the streets and gardens. The town, comprising several quarters, lies in the south-west part of the oasis, where have been sunk the wells on which the inhabitants depend for their supply of water. The chief spring fills a vast basin of Roman construction. Usually known as the fountain in a superlative sense [ain in Arabic, and tit in Berber), it is more specially named the Ain-el-Fers, the "Mare's Spring," or, in the local Temahaq dialect, the Arsh-Shuf, or "Croco- dile's Spring." Its slightly thermal water (85° to 86" F., or about 17° "higher