The roaring had increased in both volume and intensity, and the machine-room had become unbearably hot. They turned toward the door, but just at the entrance into the passage a pile of debris had descended, making egress impossible. Behind them the roaring increased still more. "Come on, boy friend," called the dancer, tearing at the rocks. "Get these out of the road unless you want to be stewed in your own juice." Together they toiled over the blocks of granite, hurling them backward toward the wreck of the machine. One minute, two, three--the roaring behind them grew and spread, the heat became terrific. * * * * * "Ah!" cried Marta Lami at last. A tiny opening at the top of the heap was before them. Sherman tugged at a rock--one more, and they would be through. But it was too big, would not budge. "No, this one," shouted his companion and together they dragged at it. It gave--a cascade of smaller stones rolled down the heap to the floor. "You first," said Sherman and stood aside. The dancer wriggled through and reached back a hand to pull him after. He dived, grunted, pushed--made it. As they turned to slide down the other side of the heap, he looked back. A little rivulet of something white, hot and liquid was creeping through the ruins of the machine and into the room. Up the passage, strewn with wreckage, but with no more blockades, into the upper machine room. The machines here also were deserted and from one of them issued a minor variation on the roaring sound they had heard in their own room. The guard was not on duty. They turned, sped up the next passage to the place where the cars ordinarily met them. The car-track was dark; by the illumination from the passage they could see the rail on which it ran, a foot or two down from the level of the passage, and about a foot broad--a single shining ribbon of metal. Sherman looked in one direction, then the other. Nothing. The roaring behind them continued. "Drive on, kid," said Marta Lami. "The boojums are going to get us if we wait." "Stop, look, listen, watch out for the cars," he quoted as they leaped down and both laughed. The roadbed was as smooth as glass, the rail set flush with it. Judging that the best route was the one taking them upward Sherman turned to the right and they began climbing, hand in metal hand. The track was on a curve as well as an ascent. After a few steps they were in complete darkness and could only feel their way along, running into the wall every few minutes. They climbed for what seemed hours. The tunnel continued dark, without branches, simply winding on and on. Finally, so quickly that Sherman missed his step, they reached a level place, rounded one more curve, and saw ahead of them a band of light across the track from some side-tunnel. "Shall we try it?" he asked as they reached the opening.