The boys had resigned their turn at the chopping and returned to the shelf by now. Again Andy and Mr. Roebach were high above their heads, clinging to the slippery wall. For the ice on this side, while it was in the shade still, was becoming moist. The heat of the day was intense. Down the opposite wall of the crevasse tumbled a sheet of water which fairly hid the ice itself. Occasionally huge blocks of the melting crystal were broken off by the action of the water and fell into the chasm with thunderous crashes. There was good reason for the party being worried over their situation. The heat increased and over the edge of the wall they sought to climb the water began to pour. Andy Sudds and the oil man were driven down from their perch. The sun appeared, blazing directly down into the crevasse and the melted ice rained in torrents about them, falling upon the _Snowbird_ as though a heavy rainstorm was in progress. They fled to the roofed cabin to escape this downpour. But they were fearful that at any moment the flying machine, resting so insecurely upon the shelf of ice, would be washed into the depths. A terrible hour followed. The heat became torrid. The splashing of the water and thunder of huge pieces of ice falling into the crack almost deafened them. Just as the sun had crossed the narrow arc above the crevasse there came a thunderous roar. Used as they had been for some hours to explosions of sound, this one made all tremble. The ice-wall seemed to crack and stagger from base to summit. The flying machine shook as though it were about to take flight. But they all knew that the only flight it could take was to the bottom of the abyss. The thunder of falling ice continued for some minutes. A mighty avalanche had fallen into the depths. But whether it had fallen from their side of the crevasse or from the other, they could not at the moment tell. The sun was out of sight. Its rays, however, still played upon the wall above their heads, while from the lower part of the gulf there rose a steam, or fog, which wrapped the flying machine around and smothered all in its embrace. The light disappeared from above. The heat of the torrid sun departed. The chill of the fog bit in like a knife. They were glad in an hour to get into their furs, and there remained shivering in the damp, cold fog, while the streams of water which had poured down the ice-wall congealed again into the hardest of crystal. Roebach and Andy possessed themselves of two storage battery lamps and went cautiously to examine the wall up which they had climbed for more than a hundred feet. It was now as smooth as glass! The wash of the falling water had worn away the ice so that the steps of their ladder had disappeared. The work they had done toward escape had gone for naught.