That night our thermometer went down to five degrees below zero, but the morning rose clear, with the warmest sun we had known for a week past. The whole party set to work digging, with any tool that came to hand, but it was to the sun we owed our discovery. Brisk runnels of water began to tinkle away down the slope, the face of the snow sagged and caved, until there appeared, fully thirty yards from the scene of our blind efforts, a curious green blotch against the white. Philipson ploughed through the soggy mess towards it with a whoop of exultation, and a moment later the three of us were dancing round the _obo_, cheering like schoolboys. There was no doubt about it being the one we sought: you could see plainly the zigzag scratches where Philipson had scraped off the dead man's message. We were now in a regular fury to be gone. Perhaps not two days off was the end of our quest, the rim of that mysterious depression we had come so far to find. Philipson at once laid out his compass and set a course due west; but at that moment I observed a strange commotion among the bearers. They were gathered in a group at some distance from where we stood, and I saw one of them point to the sky with an expression of downright terror. Excited as I was, I half expected to see one of the monstrous birds of the legend flap out over the peak surrounding us, but it wasn't that. It was a black cloud, no bigger than the cloud of holy writ, but curiously distinct from anything I had ever seen before. It was expanding swiftly under our eyes, and looked, on a gigantic scale, exactly like a big blob of ink that has fallen on to a blotter. But the really astonishing thing about it was the speed with which it was approaching. 'Great Scott!' gasped Poyning. 'It's coming up as fast as a train!' If I hadn't seen this type of cloud before, Philipson evidently had, and recognised it for something dangerous. He instantly ordered the tents, which had just been taken down, to be opened out and erected again length-wise--one wall of canvas five or six-fold and about six yards long. Every rope and peg we possessed we used to secure this one shelter, and concentrated our whole camp under the lee of it. These preparations were rushed through, but none too soon. With a shriek the storm was upon us, first a terrific blast of wind, then a withering burst of hail, then thunder; and after a while, when the very snow was scoured off the barren steeps by the force of the tempest, blinding clouds of sand and grit that stung the skin like spirts of flame. It was a brand of storm, as I say, new to my acquaintance, and even in the rush and howl of it all I couldn't help noticing with astonishment that although the thunder crashed like the splitting asunder of mountains, we saw from first to last no sign of lightning.