Giddy, half fainting, she paused irresolutely, attempted, perhaps, to turn back, and sank upon the bridge with a sob of genuine terror, clinging to the smooth iron track and hiding her face in her hands. As she did so, she heard a peculiar, vibrating hum in the rail that sent the blood to her heart. Behind her, in their safe position on the embankment, the rest heard it, too, and, looking up, saw what was coming. The Boston express, with a long and heavily loaded train, was at that very moment rounding a curve not a mile above the trestle, and rushing upon them, a roaring, resistless avalanche of iron. [Illustration: “THE TRAIN, TOO, WAS ON THE BRIDGE.”] Lou felt as if she were in a nightmare. She tried to move, but was as motionless as if she were lashed to the bridge. As if in a bewildering dream, she faintly caught the sound of her companions’ cries of terror and warning; in a bewildering dream, she heard two shrill notes echoing and re-echoing from the mountains far and near, and knew it was the agonized shriek of the great, laboring locomotive, powerless to prevent what the rocks below were waiting for. She had read in books of people who, in extreme peril, saw the details of their past life like a flash; with the wet iron rails quivering and twanging more and more loudly under her hands, she knew what it meant. But even while the last accents of the whistle were sobbing themselves away in the distance, there came a sound of footsteps, light and swift. Two strong arms seized the girl about the waist, and, still, as if in a strange dream, she knew it was the languid, delicate Fred who was running with her in his arms along that fearful height. A few moments later, a hollow roar and tremulous movement under his feet told that the train, too, was on the bridge. When Fred leaped from the track, upon the farther side, the locomotive was not forty feet behind them. The engineer’s pale face stared at them an instant from the cab; then the train, with groaning brakes, smoking axles, and a shower of cinders, thundered past and was gone. Not one of the passengers knew of the escape, or even of the danger. It was afterward learned, however, that the appliances of the air-brake on the engine would not work that day, and the train, with its tremendous acquired momentum, ran to Bemis station, nine miles below, before it could be brought to a standstill. With half-closed eyes, Lou lay helplessly on the mossy plot where Fred had placed her, and, in the slow waking from her dream, she watched him as he went to and fro, at first beckoning and making motions for the rest to join him by crossing the bed of the brook, and then confining his attention entirely to her.