The ravine, up which the maherry had carried the old man-o'-war's-man, ran perpendicularly to the trending of the seashore, and almost in a direct line from the beach to the valley in which was the Arab encampment. It could not, however, be said to debouch into this valley. Across its mouth the sand-drift had formed a barrier, like a huge "snow-wreath," uniting the two parallel ridges that formed the sides of the ravine itself. This "mouthpiece" was not so high as either of the flanking ridges; though it was nearly a hundred feet above the level of the beach on one side, and the valley on the other. Its crest, viewed _en profile_, exhibited a saddle-shaped curve, the concavity turned upward. Through the centre of this saddle of sand, and transversely, the camel had carried Bill; and over the same track the three midshipmen had gone in search of him. They had seen the Arab tents from the summit of the pass; and had it been daylight, need have gone no nearer to note what was being there done. Even by the moonlight they had been able to make out the forms of the horses, camels, men, and women; but not with sufficient distinctness to satisfy them as to what was going on. For this reason had they descended into the valley, creeping cautiously down the slope of the sand-wreath, and with equal caution advancing from boulder to bush, and bush to boulder. On taking the back track to regain the beach, they still observed caution, though perhaps not to such a degree as when approaching the camp. Their desire to put space between themselves and the barbarous denizens of the desert, of whose barbarity they had now obtained both ocular and auricular proof, had very naturally deprived them of that prudent coolness which the occasion required. For all that, they did not retreat with reckless rashness; and all three arrived at the bottom of the sloping sand-ridge without having any reason to think they had been observed. But the most perilous point was yet to be passed. Against the face of the acclivity, there was not much danger of their being seen. The moon was shining on the other side. That which they had to ascend was in shadow, dark enough to obscure the outlines of their bodies to an eye looking in that direction, from such a distance as the camp. It was not while toiling up the slope that the dreaded detection, but at the moment when they must cross the saddle-shaped summit of the pass. Then, the moon being low down in the sky, directly in front of their faces, while the camp, still lower, was right behind their backs, it was not difficult to tell that their bodies would be exactly aligned between the luminary of night and the sparkling eyes of the Arabs, and that their figures would be exhibited in conspicuous outline.