Taking a fresh grip on his quivering nerves, Nelson cautiously cocked the .38-55, cuddled the familiar stock to his shoulder. He sighted, then with his right hand pushed down the catch lever of the flashlight. Instantly a dazzling white beam shot forth to shatter the gloom. The hair on the back of Nelson's hands itched unbearably, while the cold fingers of madness clutched at his brain, for the sight which met his eyes all but bereft him of his wavering sanity. There, belly up, across a low ridge of basalt, lay a hideous reptile, which in form faintly resembled an enormous and fantastic kangaroo. Its scabby belly was of the unhealthy yellow of a grub, a hue which gave way to a leaden gray as the wart-covered skin reached the back. Two enormous hind legs, each thick as a man's torso and each equipped with three dagger-like talons, struck out in helpless fury at the air, while a long, lizard-like tail threshed powerfully back and forth, scattering ponderous boulders right and left as though they had been marbles. The flashlight being trained as it was, the monster's head and forequarters were invisible, all save two very much smaller and shorter front legs which, like the hinder ones, clawed spasmodically. "The D. T's!" gasped Nelson, conscious that he was trembling like an aspen. He suppressed a wild desire to laugh. "Yes, I've gone crazy!" * * * * * He glanced downwards and leaped swiftly back, for, creeping over the stones towards his fur outer boots, meandered a wide rivulet of bright scarlet blood. From its surface rose small curling feathers of steam which, drifting towards the tunnel's roof, merged with that gray, vaporous current flowing steadily towards the sunless Arctic expanse outside. It took Nelson a long five minutes to sufficiently recover his equilibrium for action. All he could do was to stare at that grotesque, gargoyle-like creature as it writhed in leisurely and persistent death throes. "Guess I winged it all right! My God, what a nasty beast! Looks like one of those allosaurs I read about in college. It couldn't be, though--that tribe of dinosaurs died out five million years ago." Cautiously he scrambled around among the high black stones, casting the search light beams before him and holding the Winchester always ready in his hand while trying to recall snatches of palaeontology studied at college long years ago. "Yes, it must be a survival of one of the carnivorous dinosaurs," he decided, then paused, increasingly conscious of that steady thudding noise. What caused it? * * * * *