"Then shoulder arms: march!" They made for the ridge of lava, climbed upon it without much difficulty, and began to ascend the gradual slope it formed, till they were shut in by the trees rising on either side, when the darkness became so intense that their progress was very slow, and they had to depend a good deal upon their spears used as alpenstocks. But one great need urged them on, and it chased away the thoughts of pursuit, and of the risks they were running. This need acted as a spur, which kept them crawling up the solidified river for fully a couple of hours, which were diversified by slips and falls more or less serious. At last, as the lava flood took a bend round toward the north, they became aware of a bright glow high above their heads, where the summit of the volcano must be, and after a remark from Ned that it looked as if a bit of the sunset was still there, Jack grasped its meaning. "It's the reflection of the fire that must be burning up at the top of the mountain." "Think so, sir? Well, I suppose it's too far off to hurt us. That's miles away." "Yes; but we are walking on one of the rivers which ran down, and these stones we keep kicking against were once thrown out." "Ah, you've read a lot about such things, sir; I haven't. Then you say it's all fire up there?" "Yes, Ned; look, it's getting brighter." "Then what's the good of our expecting to find water?" "Because so many springs rise in mountains, and so much water condenses there. Hark! what's that?" Ned listened. "Can't hear anything, sir." "Not that?" cried Jack, whose senses seemed to be sharpened by his needs. "No, sir, nothing at all." Jack made no remark, but pressed on with more spirit than he had before displayed. Then he stopped short in the darkest part they had encountered, a place where the trees encroached so much from the forest on either side that they seemed to be completely shut in. "Now can you hear it, Ned?" cried the boy triumphantly. "Yes, sir, I can hear it now--water, and a lot of it falling down the rocks. It must be there just below." Ten minutes after they had lowered themselves down amongst the trees, to where in the darkness they could lie flat at the edge of a rocky basin, scooping cool, sweet water with one hand, and drinking with a sense of satisfaction and delight such as they had never experienced before. "There, Mr Jack," said Ned joyously, "I don't know what you think, but I say that it's worth going through all the trouble we've had for a drink like that. Here goes again." He bent down over the stone basin, scooping up the water with his hand. "Have another, Mr Jack, sir," he cried. "That first one was nothing. It's coming down over the fall sweeter and fresher than ever." Jack, nothing loth, went on drinking again, but in a more leisurely manner.