By superhuman effort he worked out the largest rock at last, backed into the cave with it, and wriggled in again to the attack. Prying and digging with his knife, he burrowed on through earth that gave way more readily as he progressed. Sweat streamed from him unheeded; with each foot that he advanced the air in the tunnel grew warmer. A nauseating, steamy odour crept into it, so faint at first as to defy analysis, but increasing momentarily. Presently Mather drew his hand back with an exclamation of surprise. His fingers had touched a rock so hot that it almost burned them. “What the hell?” he growled, then lay still, thinking, his chest heaving as he gasped for breath. Crushingly the explanation came to him: The burrow was leading into the mountain, straight forward toward those infernal caverns of molten lava and steam which underlie that whole mighty continental backbone from Cape Horn to Panama. Already he had dug far enough through the mountain’s outer shell to reach the heat that radiated from them. Mather’s heart sank with the realization that all his work had gone for nothing. Then a great wave of hope swept over him as the thought came that out of this very failure sprang success, for since he had been digging toward the mountain’s centre, the opposite way must lead to light and life and freedom. He wormed his way backward, gulping with relief as he reached the cooler air near the tunnel’s mouth. A few more wriggles, and his knee struck something that crushed flabbily under the pressure. Across one hand dragged a fat, rough body, paused and sent a tingle of pain up his forearm as he shook it off with a jerk. The spider army had returned. Through the endless hours of that second night of horror John Mather clung to two things with the desperation of a wave-buffeted man whose arm is crooked across a slippery, floating spar: the knowledge that daylight would bring relief from his tormentors, and the hope that before another evening drove them scurrying back to shelter he would have won his way through the cave wall. Every atom of will power, every drop of that fine essence of determination which some men call upon to carry them against impossible odds he threw into the mental struggle, knowing that to lose sight of his goal would mean gibbering madness. And in the end he won. Taut and quivering as a plucked string, he sensed rather than saw that the crawling hosts were gone. “Now!” he rasped, the sound of his own voice grating across his nerves. “Now you dig.” He hurled himself savagely into the work, slashing and tugging at the hard-packed earth and stone opposite the mass of débris he had scooped out the day before. His knife wedged between two rocks and the blade snapped short off as he tried to extricate it. He cursed chokingly and hacked away with the haft, pitifully futile by comparison. “Got to make it!” he muttered. “Got to make it to-day! I’ll go crazy--_crazy_, I tell you!”