This mountain I perceived, from the foot to the summit, to be covered with detached stones, such as wholly constitute the lower hills. The small plain from which this mountain rose, was encompassed by rows of hills, such as above described, closely running into each other, and connected as a wall. The flat within was overspread with white quicksand, on which lay, irregularly scattered, large blocks of stone, of like nature and substance as that generally throughout this desert. With some trouble I procured a sample of the earthy stratum beneath the sand: it seemed to me, at the time, to have the appearance of ashes thrown out from a volcano; but I have since lost the paper which contained the specimen, and cannot further confirm the accuracy of my first observation. In the vicinity of this mountain, I found stones of smaller bulk and a reddish colour, resembling that of burnt bricks; some of these were one-half red, the other blackish; the red part had not the same weight or density, on fracture, as the black: the former is more porous and spongy, and bears a general resemblance to slags or scoriæ. The stony substance, of which the mass of these mountains consists, varies in colour and density; in some parts heavy and compact, in others having small holes and cavities. These species of stone are intermingled, and I could not discover in either, any extraneous matter or substance. The stratification or lay of these stones is perfectly horizontal, but often disturbed; parts of the first layer sinking into and mixing with the second below, and the second with the third. Sometimes the strata take an oblique direction; sometimes are promiscuously confused, and sometimes no strata appear at all; and a series of low hills is formed of one solid mass of rock, with fissures in direction to the north. The plain too shews occasionally level rock of the like nature and substance, in parts where bare of sand or soil. The whole of this region of hillocks, hills, rocks, and mountains, is, in parts, intersected by vales, occasionally having water; and though the soil is of white sand, yet it is so far fertile as to produce single trees, and pasturage for beasts; in these productive spots are frequently to be seen the tracks and slots of game. Often, when I thought I could so do without danger of losing my way, I struck into one of the narrow vales running apparently in the same direction as our caravan road; and occasionally led away to defiles becoming more narrow and rugged, I repented my indiscretion, whilst thus separated from my company, and exposed to attack from Bedouins, with dependence for safety on my single sabre and pistols. On regaining the caravan, it yet occurred that my danger had not been great, for what Arab robber could look for a traveller in such a tract, or suppose any hardy enough to wander therein from his troop, excepting, indeed, some wretched Moroccan pilgrim in search of water!