Jôf and Meskakeh are still flourishing towns, but I have reason to think their population has been over estimated by Mr. Palgrave. I cannot put the total number of houses in Jôf at more than 500, nor in Meskakeh at more than 600, while 100 houses are an ample allowance for Kara and the other hamlets of the Jôf oasis. This would give us a census of hardly 8,000 souls, whereas Mr. Palgrave puts it at 40,000. I do not, however, pretend to accuracy on this point.
With regard to the geology of the Hamád and the adjacent districts north of the Nefûd, I believe that sandstone is throughout the principal element. In the extreme north, indeed, limestone takes its place or conglomerate; but, with the exception of a single district about 100 miles south of Meshhed Ali on the Haj road, I do not think our route crossed any true calcareous rock. The cliffs which form the eastern boundary of the Wady Sirhan are, I think, all of sandstone, south at any rate of Jebel Mizmeh, as are certainly the hills of Jôf and Meskakeh, the rocks of Aalem and Jobba, and all the outlying peaks and ridges north-west of Haïl. These have been described as basaltic or of dark granite, the mistake arising from their colour which, though very varied, is in many instances black. The particular form of sandstone in which iron occurs, seems indeed to acquire a dark weathering with exposure, and unless closely examined, has a volcanic look. I do not, however, believe that south of latitude 31° the volcanic stones of the Haura are really met with; unless indeed it be west of the Wady Sirhan. Jebel Mizmeh, the highest point east of it, is alone perhaps basaltic. The whole of the Jôf district reminded me geologically of the sandstone formation of Sinaï, both in the excentric outline of its rocks, which are often mushroom shaped, and in their colour, where purple, violet, dark red, orange, white and even blue and green are found, the harder rock assuming generally an upper weathering of black. I can state positively that nothing basaltic occurs on the road between Jôf and Jebel Aja. Of Jebel Mizmeh I am less certain, as I did not actually touch the stone, but, if volcanic it be, it is the extreme limit of the Harra southwards. The tells of Kâf I certainly took to be of basalt when I passed them. But I did not then consider how easily I might be mistaken. On the whole I am inclined to place latitude 31° as the boundary of the volcanic district east of the Wady.
The bed of the Wady Sirhan is principally of sand, though in some places there is a clayey deposit sufficient to form subbkhas, or salt lakes, notably at Kâf and Ithery. About three days’ journey E.S.E. of Ithery, I heard of quicksands, but did not myself cross any ground holding water. The sand of the Wady Sirhan, like that of all the hollows both of the Hamád and of northern Nejd, is nearly white, and has little to distinguish it from the ordinary sand of the sea shore, or of the Isthmus of Suez. It is far less fertile than the red sand of the Nefûd, and is more easily affected by the wind. The ghada is found growing wherever the sand is pure, and I noticed it as far north as Kâf. In some parts of the Wady which appear to hold water in rainy seasons, there is much saltpetre on the surface, and there the vegetation is rank, but of little value as pasture. In the pure white sand, little else but the ghada grows. Wady Sirhan is the summer quarters of the Sherarat.
The Harra is a high region of black volcanic boulders too well known to need description. It begins as far north as the latitude of Damascus, and stretches from the foot of the Hauran hills eastward for some fifty miles, when it gives place to the Hamád. Southwards it extends to Kâf, and forms the water shed of the plain east of the Wady Sirhan. According to Guarmani, it is found again west of the Wady, as far south as Tebuk. The eastern watershed of the Harra would seem with the Jebel Hauran to feed the Wady-er-Rajel, a bed sometimes containing running water, and on its opposite slope the Wady Hauran which reaches the Euphrates. The Harra is more plentifully supplied with water than the Hamád, and has a reputation of fertility wherever the soil is uncovered by the boulders.
The Nefûd.—A little north of latitude 29′, the Hamád, which has to this point been a bare plain of gravel broken only by occasional hollows, the beds of ancient seas, suddenly becomes heaped over with high ridges of pure red sand. The transition from the smooth hard plain to the broken dunes of the Nefûd is very startling. The sand rises abruptly from the plain without any transition whatever; and it is easy to see that the plain is not really changed but only hidden from the eye by a super-incumbent mass. Its edge is so well defined that it is hardly an exaggeration to say that with one foot a man may stand upon the Hamád, and with the other on the Nefûd; nor is there much irregularity in its outline. The limit of the sand for several hundred miles runs almost evenly from east to west, and it is only at these extremities that it becomes broken and irregular. Such, at least, I believe to be the case; and if, as seems probable, the whole drift of sand has been shaped by prevailing easterly winds, the phenomenon is less strange than might be thought.
The great Nefûd of Northern Arabia extends from the wells of Lina in the east to Teyma in the west, and from the edge of the Jôf basin in the north to the foot of Jebel Aja in the south. In its greatest breadth it is 150 miles, and in its greatest length 400 miles, but the whole of this is not continuous sand. The extreme eastern portion (and perhaps also the extreme western) is but a series of long strips, from half a mile to five miles in breadth, running parallel to each other, and separated by intervening strips of solid plain. Nor is the sand everywhere of equal depth; the intermittent Nefûds are comparatively shallow, and would seem to bear a certain proportion in depth to the breadth of the strips. Thus the highest sand ridge crossed by the Haj road is barely eighty feet, while others are but fifty and twenty feet. The continuous Nefûd on the other hand, between Jôf and Haïl, has a depth of at least two hundred feet. The intermittent ridges may possibly suggest an explanation of the original formation of the mass. It would seem as if the wind acting upon the sand drove it at first into lines, and that, as these grew broader and deeper, they at last filled up the intervening space, and formed themselves into a continuous mass at their lee end. If this be the case, the intermittent ridges show the direction in which the solid mass of sand is advancing, the direction, that is, contrary to that of the wind. I leave this deduction, however, to more competent persons than myself to draw, contenting myself with recording the fact.
The red sand of the Nefûd is of a different texture from the ordinary white sand of the desert, and seems to obey mechanical laws of its own. It is coarser in texture and far less volatile, and I am inclined to think that the ordinary light winds which vary sandy surfaces elsewhere leave it very little affected. A strong wind alone, amounting to a gale, could raise it high in the air. It is remarkable that whereas the light white sand is generally found in low hollows, or on the lee side of hills, the red sand of the Nefûd has been heaped up into a lofty mass high above the highest part of the plain. The Hamád where the Nefûd begins is 2,200 feet above the sea. No traveller can see this desert of red sand for the first time without acknowledging its individuality. It is as little like the ordinary sand dunes of the desert, as a glacier is like an ordinary snow field in the Alps. It seems, like the glacier, to have a law of being peculiar to itself, a law of increase, of motion, almost of life. One is struck with these in traversing it, and one seems to recognise an organism.
The most remarkable phenomenon of the Nefûd are the long lines of horse-hoof shaped hollows, called fuljes, with which its surface is pitted; these are only observable where the sand has attained a depth of from 80 to 100 feet, and are consequently seldom found in the intermittent portion of the Nefûd; while it is remarkable that in the very centre of all, where it might be supposed the sand was deepest, the fuljes are less deep than towards the northern and southern edges, while the lines in which they run become more regular. Indeed, for some miles on either side of Aalem, which marks the centre of the Nefûd, there are no large fuljes; but their strings are so regular as to form, with the intervening spaces, a kind of shallow ridge and furrow running nearly east and west, and not altogether unlike, on a gigantic scale, those ridges in which meadows are sometimes laid down in England. From the top of Aalem this formation was very distinct.
The fuljes themselves are singularly uniform in shape, though varying in size. They represent very closely horse tracks on an enormous scale, that is to say a half-circle, deep at the curved end or toe, and shelving up to the level of the plain at the square end or heel. The sides of the former are as precipitous as it is in the nature of sand to be, and they terminate abruptly where they meet the floor of the fulj. This floor, sloping downwards towards the toe at an angle of about 70°, and scored with water-courses converging to a centre, roughly represents the frog, so that in plan the whole hollow would appear as in the woodcut A; while in section it would appear as in woodcut B. It is necessary, therefore, in entering a fulj on horseback, or with camels, to approach it from the east; but on foot one can slip down the sand at any point. I noticed that just west of the deep fuljes there is generally a high mound of sand, which adds considerably to their apparent depth and to the delusion of their being artificial in their origin, as though the sand scooped out has been thrown up by a digger.