After marching about six miles, we entered a gorge called Umm el-Bíbán, "the Mother of Gates," formed by the stony spurs of the Wady bank: the number of birds and trees, especially in the syenitic valleys, showed that water could not be far off. At 10.10 a.m. a halt was called at the half-way place, a bay or hollow in the left cliff, El-Humayrah--"the Little Red"--an overhanging wall of ruddy grit some eighty feet high, with strata varying in depth from a few lines to as many fathoms, all differing in colour, and all honeycombed, fretted, and sculptured by wind and rain. Above the red grit, weathered into a thousand queer shapes, stood strata of chloritic sand, a pale yellow-green, and capping it rose the usual dull-brown carbonate of lime. Large fossil oysters lay in numbers about the base, suggesting a prehistoric feast of the Titans. Amongst them is the monstrous Tridacna (gigantea), which sometimes attains a growth of a yard and a half; one of these is used as a bénitier at the church of Saint Sulpice, Paris. Amongst the layers were wavy bands of water-rolled crystals, jaspers, bloodstones, iron-revetted pebbles, and "almonds," which, in the Brazil, accompany and betray the diamond.[EN#101] We had no time to make a serious search; but, when the metals shall be worked, it will, perhaps, be advisable to import a skilled prospecter from the Brazil or the Cape of Good Hope. At noon we met the "heaven-sent, life-sustaining sea-breeze;" and now the broad and well-marked Wady Makná, with its rosy-pink sands, narrowed to a gut, flanked and choked on both sides, north and south, by rocks of the strangest tricolour, green-black, yellow-white, and rusty-red. The gloomy peak, which had long appeared capping the heights ahead, proved to be the culmination of a huge upthrust of porphyritic trap. Bottle-green when seen under certain angles, and dull dead sable at others, it was variegated by cliffs and slopes polished like dark mirrors, and by sooty sand-shunts disposed at the natural slope. Crumbling outside, the lower strata pass from the cellular to the compact, and are often metalliferous when in contact with the quartz: at these Salbandes the richest mineral deposits are always found. Set in and on the black flanks, and looking from afar like the gouts of a bloodstone, are horizontal beds, perpendicular spines, and detached blocks of felsitic porphyry and of rusty-red syenite, altered, broken, and burnt by plutonic heat. In places, where the trap has cut through the more modern formations, it has been degraded by time from a dyke to a ditch, the latter walled by the ruddy rocks, and sharply cut as a castle-moat. And already we could see, on the right of the Wady, those cones and crests of ghastly, glaring white gypsum, which we had called "the Hats."