Ralph gave a sudden gasp. He had watched every movement of the machinery. To his expert, careful ear every sound and quiver had conveyed a certain intelligent meaning. Now, however, No. 93 was emitting strange noises--there was a new sound, and it boded trouble. It came from the driving rod. Roberts caught the grinding, snapping sound, stared hard from his window, craning his neck, his eyes goggling, and then drew back towards the tender with a shout: "Go easy, Fairbanks; something's tearing loose--look out!" The warning came none too soon. Ralph slipped from his seat and dropped backwards into the tender just in time. A giant steel arm had shot through the front of the cab. It was the right driving rod. It came aloft and then down, tearing a great hole in the floor. It shattered the cab to pieces with half a dozen giant strokes. It smashed against the driving wheels with a force that threatened to wreck them. Then it tried to pound off the cylinder. The flying arms next took the roof supports, snapping them like pipe stems, and buried the fireman in a heap of debris. "Jump!" gasped Roberts. "I stay," breathed Ralph. And, stripped of everything except her cylinder, No. 93 dashed on--a wreck. CHAPTER XVI THE WRECK The battered locomotive continued its course for nearly half a mile, with engineer and fireman crouching back on the coal of the tender. There was a diversion of the circling driving rod as the pace slackened. Then a violent hissing sound told of a leak somewhere in the machinery. The great steel locomotive slowed down like a crippled giant. "She's dead," said Roberts, choking a queer sound way down in his throat. "Old 93!" Ralph jumped to the ground and the fireman after him. The latter went all around the stalled locomotive, shaking his head mournfully. Ralph hastened ahead out of the glare of the headlight and peered down the rails. For nearly two minutes he stood, shading his eyes with one hand to bring the disappearing runaway within focus. The wild engine had sped on its way untrammeled. He made out that she had slowed up. In the distance he fancied he saw a brisk form spring from the cab. Ralph figured it out that a switch had been set. Then the runaway started again. He fancied that some one jumped from the cab after the engine had got in motion. He could catch the sharp clack-clack of the flying wheels ringing in the distance. "She is running wild now," murmured the intent young railroader, and then started with a shock. A horrid clamor extended out. It must have been a mile away, but the air was death-like, it was so still, and the merest sound seemed to vibrate clearly. Crash, crash, crash! It sounded as if a building had collapsed against other tottering structures, tumbling them all into a mass of ruins.