"It could not be thunder," said Jack. "Oh yes, it could," said the captain. "I've heard short sharp cracks like that often out here, but I don't think that was thunder." "Must have been," cried the doctor. "Why, I saw the flash. There! Look!" A bright light suddenly appeared from somewhere inland, followed at a few seconds' interval by a heavy detonation, exactly like the firing of a great gun. "Now what do you say, Captain Bradleigh?" cried Sir John. "That it is what I thought at first, sir. The mountain yonder is firing a shot or two. If we had been out at sea, I dare say we should have seen a great red-hot stone flying up and falling back." "Then there is going to be an eruption," cried Jack in excited tones. "That does not follow at all. Some of these volcanoes do no more perhaps than make a rumbling, and send up a few red-hot stones now and then. Forward now, gentlemen. Close up, my lads, and follow two and two." The mountain, if the captain was right, made no farther sign, and now began the most interesting part of the journey. With the exception of having to be careful not to stumble over the blocks of coral limestone which lay here and there in their road, it was easy walking in spite of the darkness, while this latter was modified by the brilliant stars overhead, the dazzling scintillations of the fireflies, which flittered out whenever any of the bushes which fringed the sands were approached-- and the soft, luminous, oil-like appearance at the edge of the lake. But the sand was soft, and it seemed to Jack as if they would never reach the boat. In the darkness Edward edged up close to his young master, and whispered-- "Tired, Mr Jack?" "Dreadfully." "Makes one's legs feel as if they were made of cast lead." "Or stones," said Jack. "Well, p'r'aps you're right, sir. Stone is more like it. Let me carry your gun, sir. Seems to get heavier every step, don't it?" "Yes; and the cartridges too. Thank you, Ned. I should be glad to get rid of them. No, you've got your own to carry, and--I say, how do you feel now? I mean, after your fall." "Oh, bit stiff, sir. There's nothing broken; but I don't go quite so well as usual. Shan't be sorry to get back to the yacht. Better give me your gun, sir." "Better give me yours to carry, Ned." "What, sir? Well, 'pon my word, Mr Jack, you do talk. I do wonder at you." Just then Jack started, for a hand was laid on his gun. "Who's that?" he cried. "Only me, sir--Lenny," said a dark figure behind him. "Let me carry your gun, and pouch too. I heerd what you said. Take hold of t'other's weapon, mate," continued the man to the sailor by him, and Jack and his man tramped the rest of the way relieved of their loads, heartily glad to hear at last a hail from somewhere away in the darkness. It came from the boat; and directly after a bright light flashed out over the calm lagoon, like a star just rising to shine across the sea, and the men gave a cheer.