It was full of sand now; but beyond all question it had once been full of water. It came, evidently, from the mountains over toward the northwest. We could trace its windings for a long way across the plain, thence through the ravine and on southward in a line parallel with the Nile. Here, beneath our feet, were the water-worn rocks through which it had fretted its way; and yonder, half-buried in sand, were the bowlders it had rounded and polished and borne along in its course. I doubt, however, if when it was a river of water this stream was half as beautiful as now, when it is a river of sand. It was turbid then, no doubt, and charged with sediment. Now it is more golden than Pactolus and covered with ripples more playful and undulating than were ever modeled by Canaletti’s pencil. Supposing yonder town to have been founded in the days when the river was a river and the plain fertile and well watered, the mystery of its position is explained. It was protected in front by the Nile and in the rear by the ravine and the river. But how long ago was this? Here, apparently, was an independent stream, taking its rise among the Libyan mountains. It dated back, consequently, to a time when those barren hills collected and distributed water--that is to say, to a time when it used to rain in Nubia. And that time must have been before the rocky barrier broke down at Silsilis, in the old days when the land of Kush flowed with milk and honey.[155] It would rain even now in Nubia, if it could. That same evening, when the sun was setting, we saw a fan-like drift of dappled cloud miles high above our heads, melting, as it seemed, in fringes of iridescent vapor. We could distinctly see those fringes forming, wavering and evaporating; unable to descend as rain, because dispersed at a high altitude by radiated heat from the desert. This, with one exception, was the only occasion on which I saw clouds in Nubia. Coming back, we met a solitary native, with a string of beads in his hand and a knife up his sleeve. He followed us for a long way, volunteering a but half-intelligible story about some unknown birbeh[156] in the desert. We asked where it was and he pointed up the course of our unknown river. “You have seen it?” said the painter. “Marrat ketîr” (“many times”). “How far is it?” “One day’s march in the hagar” (“desert”). “And have no Ingleezeh ever been to look for it?” He shook his head at first, not understanding the question; then looked grave and held up one finger. Our stock of Arabic was so small and his so interlarded with Kensee, that we had great difficulty in making out what he said next. We gathered, however, that some howadji, traveling alone and on foot, had once gone in search of this birbeh and never come back. Was he lost? Was he killed? Who could say? “It was a long time ago,” said the man with the beads. “It was a long time ago and he took no guide with him.”