All at once Nelson checked his pathetically slow progress, finding himself on the top of an eminence, looking down in what appeared to be a vastly deep natural amphitheater of snow and ice. At the bottom, and perhaps a hundred yards distant, was a curious black oval from which appeared to rise a dense, wind-whipped column of whitish vapor. "My eyes must be going back on me," muttered Nelson through stiffened lips. How intolerably heavy his fur suit seemed! His strength was about gone and that curious black mouthlike circle seemed infinitely far away. But, spurred by fears for his friend, he started downward for the precipitious trail leading directly towards it. Once he stepped inside the crater, he became conscious of a terrific side pressure which gripped him as a whirlpool seizes a luckless swimmer. The wind buffetted him from all angles, dealing him powerful blows on face and body, which, too strong for his weary body, sent him reeling weakly, drunkenly across the hard, glare ice towards the vortex. Twice he slipped, each time finding it harder to arise. But at last he approached what on closer inspection proved to be a subterranean vent of black rock. "Steam!" he gasped. "It's steam coming out of there!" * * * * * Swayed by a dozen conflicting emotions, he paused, the Winchester barrel wavering like a reed in his enfeebled grasp. "The whole thing's crazy," he decided. "I must be frozen and lying somewhere, delirious. Poor Dick! Can't help him much now." Like a man in a nightmare who advances but feels nothing under his feet, Nelson staggered on towards that huge, gaping aperture of black rock. On the threshold a pool of melted snow water made him stare. "Hell!" he said. "It's only a volcanic vent of some kind." Then dimly came the recollection of Eskimo legends concerning thermal springs beyond the desolate and unknown reaches of Grant Land. His mind in an indescribable turmoil, Nelson splashed across a hundred yards of sodden snow, then shivered on wading knee deep through a pool of melted ice. Now he stood on the very threshold of that awful opening, dense clouds of vapor beating warmly against his chilled features. His goggles fogged at once, blinding him effectively as, with reason staggering under the accumulated stress of starvation and the circumstances of Alden's disappearance, he groped his way a few feet into the vent. With his left hand he pulled up the glasses from his sunken, blood-shot eyes. "It's warm, by God!" he cried in astonishment as the skin exposed by lifting the goggles came in contact with the air. "Must be some kind of earth-warmed cave." * * * * *