“We can’t go that way now,” said Alan “I am afraid it’s too large to tackle. Why it must be thirty feet long at least. We shall have to go back.” Then came the most horrible experience the cousins had ever had. The most awful. The most terrifying. “Run,” cried Alan. “If we can get into the passage beyond we may be able to block up the way and prevent it coming through after us.” They reached the narrow opening, and all around were huge blocks of rock and stone which they piled up one on top of the other. “Only one more is needed,” cried Alan triumphantly. But he spoke too soon—a large, flat head, perhaps a foot and a half in length, with ugly eyes glowing like live fire, shot through the opening, and watched them. The mouth was open wide and the forked tongue shot rapidly in and out in venomous fury. The smell was terrible, whether from its breath or permeating through its skin from its body, they could not tell, but it made them feel giddy, sick and ill. For perhaps ten minutes (if time could be measured in that awful place) it remained there motionless, and then gradually the stones came tumbling down as it forced its way through the barricade. The boys watched their horrible foe. They were powerless. Escape was impossible, for behind them was a narrow passage, perhaps a mile in length, that offered no shelter. Would it never attack them? Why keep them in this awful suspense? “Knife,” came suddenly from between Alan’s tightly compressed lips. Then after a moment, during which time he opened the well worn blade—“There are plenty of stones behind?” “Plenty.” Swiftly followed the instructions. “Pick up the largest you can handle—both of you—when I give the word dash them at the brute’s head. It is our only chance—then rush past the head.” “But—” commenced Desmond. “Don’t argue—it’s our only hope. The thing is too big to turn round in this small space. It _must_ go on. Once we get past it we may stand a chance.” Alan never relaxed his watchful gaze. Suddenly the reptile lowered its head and an ugly hiss came from its mouth. “Now,” cried Alan, and as he hurled the knife, harpoon-like into the open mouth two heavy stones came crashing down on its skull. The sudden onslaught dazed the creature, and its head dropped to the ground. Quickly they rushed past it, but they all realized that they were not yet out of danger. The passage they were in was very narrow and the serpent was so immense that it was impossible for them to stand without feeling the clammy skin next to them. Jez-Riah shuddered. “What will become of us?” she moaned “It is too big to kill.” And indeed, it seemed to be, for Alan had not exaggerated. The length was quite thirty feet, and the girth of its middle was perhaps ten feet, narrowing to two at the tail.