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Rh CENTRAL PLATEAU.] ARABIA 239 which the traveller must of necessity cross before lie reaches the inner region. It is this very desert that, having been often witnessed on its outer rim, but never traversed from one side to the other by Greek or Roman, or even, in the greater number of instances, by modern explorers, has given occasion to the belief that central Arabia was itself little better than an expanse of uninhabitable waste, an idea expressed by the Arabia Deswta of the ancients, and often repeated by later writers. .e north- This desert, on the north and north-east, where it extends i desert. f rom Syria and the Hejaz inwards, is a region of hard gravelly soil, from which circumstance it has derived the elastic title of &quot; Petraea.&quot; It is diversified here and there by belts of sand, with occasional patches of stunted bush and thin grass, indicative of moisture at some depth below; the sand, too, affords rooting for a feathery euphorbia, the &quot; ghada ; of the Arabs, a favourite browse of camels. The general height of this tract, backed up as it is by the Syrian plateau on the north, and the Sherd mountains on the west, appears to vary from 1000 to 2000 feet above the sea. Eastward it slowly slopes down to the level of the Persian Gulf. A long serpentine depres sion, beginning in the Syrian territory near Palmyra, traverses it in a south-easterly direction ; this is Wadi Seihan, or the &quot; Valley of the Wolf,&quot; leading to the deep oval hollow of Jowf, with its oasis of palms and gardens. A more extensive but shallower depression to the west forms the oasis of Teynia, known to Hebrew chroniclers. South of Jowf and Teynia the desert changes its stony to a sandy character, and its surface is heaped up by the winds into vast ridges, called the Nefood or &quot; passes,&quot; not to be crossed without some danger; for, besides the almost absolute want of water, a few scanty and brackish wells of which, separated one from the other by intervals of GO or more miles, alone exist, it is here that the ie &quot;simoom,&quot; or poison wind, often blows a phenomenon, noon. entirely distinct from the customary &quot; shelook,&quot; or sirocco, of the south, much as a hurricane differs from an ordinary gale, though the two have been occasionally confounded in popular writings. The simoom is a peculiar condi tion of the atmosphere, resembling in all essential points a cyclone. As in the cyclone, the central space, or the simoom itself, is calm, but is occupied by a gas unfit for respiration ; while round this as a centre, slowly travel ling on, there eddy violent gusts of heated air, Like those of a furnace, though it is not to them, but to the compara tive vacuum which they surround, that the simoom owes its suffocating quak ties. It approaches slowly amid the whirl of air currents that precede it for some distance; its violet colour announces it when actually near. During its presence the only chance of preserving life till the mephitic vapour has passed over, is found in covering the face with a cloth and lying prone on the sand, thus to inhale what little atmospheric air still exists in the upper ground stratum, and thus to maintain the breath till the period, varying from two to ten minutes, of the poison column be gone by ; meanwhile the feeling in the chest is that of suffocation, and that in the limbs as if molten iron were being poured over them. Camels instinctively bury their muzzles in the sand during the simoom; but horses are said not to possess the same preservatory instinct, and to perish in consequence. The precise nature of the phenomenon, and its origin, are subjects of conjecture; but its general character, that of an eddy of heated atmo sphere around a central space occupied by a deleterious gas, the whole travelling at a slow rate, and generally from south or east to north and west, is not to be mistaken, out tains South of the Nefood begins a series of granite hills, at Shomer. first cropping up as mere isolated rocks through the sand, then increasing in extent and height till they coalesce and form the two parallel chains of Jebel Aja and Jebel Solrca, both of which cross two-thirds of the peninsula from N.N.E. to S.S.W. The highest peak of either does not seem to exceed 4000 feet above the sea-level. Between them and around their base extend broad and well-peopled valleys. The irrigation is wholly artificial and from wells, which here yield an abundant supply. The water is brought up from an average depth of 20 or 30 feet. The climate of this region, though heated by the neighbouring desert, is remarkably healthy, and the air extremely pure. Passing this mountain-belt, we find a second depression, The still following the same general direction, namely, from Kaseem. N.N.E. to S.S.W., wide and fertile, a land of palm-trees, gardens, and wells; the soil is here and there streaked with sand, but no mountains or even rocks of considerable size occur anywhere. Towards the east the level of this region gradually rises upwards to the Toweyk range, by which it is ultimately shut in. Westward it slopes down wards, and at last opens out on the Hejaz near Medinah. The general level is low, not exceeding 1000 feet above the level of the sea, and the temperature hot; it is altogether the most productive, but at the same time the least healthy region of central Arabia. Water abounds throughout the greater part of its extent, at a level of only a few feet below the ground, and occasionally collects on the surface in perennial pools, none of which are, however, large enough to deserve the name of lakes. The most thickly peopled section of this valley is called Kaseem. North-east of it rises the mountain chain of Toweyk, Mountain running almost due south, and keeping at a distance vary- chain of ing from 100 to 200 miles from the Persian Gulf. This Towe &amp;gt; k - constitutes the backbone of the Arab peninsula, which rises up to it first by a rapid ascent from the coast, and then by a succession of more gently graduated plateaus and valleys from the east and west. Thus the wider half of the peninsula itself lies, not, as has been erroneously stated, to the east, but to the west of the principal water shed. The Toweyk or &quot;complication&quot; chain, so called from the labyrinthine character of its numerous gullies and Physical gorges, is a broad Limestone table-land, and at no point character rf exceeds, so far as has been roughly estimated, the limit of tie 5000 feet in height; it covers an extent of 100 and more miles in width; its upper ledges are clothed with excellent pasturage; and its narrow valleys shelter in their shade rich gardens and plantations, usually irrigated from wells, but occasionally traversed for some short distance by running streams. Except the date-palm, the &quot;ithel&quot; or larch, already described, the &quot; markh,&quot; a large-leaved spreading tree, the wood of which is too brittle for con structive purposes, and some varieties of acacia, the plateau produces no trees of considerable size ; but of aromatic herbs and bright flowers, among which the red anemone or &quot;shekeek&quot; is conspicuous, this region is wonderfully productive, so much that Arab writers justly praise the sweet scent no less than the purity and coolness of its breezes. The simoom or poison wind of the low lands and deserts is here unknown; even the sirocco, when it occurs, is comparatively bearable. No signs of volcanic action or hot springs are found within this region, and the mountain strata are ordinarily horizontal ; the sides of the plateaus are, however, very abrupt, often forming precipices of 200 to 300 feet in height, cut out in chalky rock. These are due to water action from torrential rains that frequently fall in spring and autumn. Immediately at the foot of. the eastern slope, which is much steeper than the western, lies a slip of desert, separ ating the highlands from the coast regions of Hassa and Kateef. The northerly part of the Toweyk plateau con tains the great province of Sedeyr, the healthiest district in all Arabia : the western slope is occupied by the pro-