The camels had halted at the foot of the hill, so we shouted down to Forsyth to bring them up, and presently we were all busy setting up camp for the night except Wrexham, who went wandering round the rocky basin. I wondered what he was doing, and when presently I saw him sitting down with a notebook I went up and asked him what he was at. “I was just calculating the size of this hollow. It’s a fine natural catchment area, as it slopes inward on every side except just the narrow south end, where it’s broken away. It forms a regular sort of trough. That probably explains why it’s so comparatively free of sand. The only sand that gets in is that blown up high by the wind, and then the prevailing wind sweeps it out at the south end again. If that end was blocked now and it did rain, we could catch enough water to give the camels a decent drink.” “Then let’s do it,” said I. “That’s just why I was figuring out the area. I make out that, if the end was blocked, this would give a yield of something like three hundred gallons from a couple of hours’ decent rain. Say two hundred, allowing for what would be sucked up by cracks. It wouldn’t require much of a stop at the end either, since the open part is narrow and the slope very gradual.” “Well, let’s do it quick. It would make all the difference to the camels if they could get a real drink. They’ve done well so far, but there’s no mistake about it they’re beginning to tire fast.” We got all hands on to it, and blocked up the end of the long, shallow, trough-like hill with stones mixed with loose sand. Not a very waterproof dam, but it might hold once it got wet. Then we sat down to wait for the rain. But none came, and at last we retired to bed, uncheered even by another glimpse of the distant snow. The air was still heavy with sand, and, though the little vistas of sky that we could see among the whirling dust were covered with lead-coloured clouds, never a grateful drop fell. That night we figured out that we should have to push on now, and trust to finding water at the end, or else turn back next day. The water--although it would have been just sufficient for men for the double journey--allowed nothing for the camels, and we had had to give them water, and realized now that they would have to be given more in future. It was three very grave-faced, unshaven men who sat discussing by the light of the hurricane-lamp. Said Wrexham finally: “If we start back to-morrow we’ve just the minimum to get us home. If we go on--assuming that we’ve passed the halfway line--we may just get to the hills as we finish our water. Then, if we don’t find it, or if the great-great-uncle’s stream has dried up--we’re done, finished. Apart from water, we’re chancing things a bit over the camels’ grub for getting back.” He looked at us as though seeking our thoughts, and for a moment or two neither of us spoke. Then I made up my mind.