“I think we are somewhere in the Atlantic; but your finding that heel-tap does puzzle me.” “We are going to have an adventure, beside which all others of our lives will pale into insignificance. I feel it in my bones. See how evenly this road has been worn and it is leading toward the centre of the island.” In a few minutes the two adventurers came to a point in the road where tall cliffs on either side stood up perpendicularly. It was dark and cold, and but a faint light from the moon shone down to them. “I don't like this,” said Johnston, who was behind the Englishman; “we may be walking into the ambush of an enemy.” “Pshaw!” and Thorndyke plunged on into the gloomy passage. Presently the walls began to widen like a letter “Y” and in a great open space they saw a placid lake on the bosom of which the moon was shining. On all sides the towering walls rose for hundreds of feet. Speechless with wonder and with quickly-beating hearts they stumbled forward over the uneven road till they reached the shore of the lake. The water was so clear and still that the moon and stars were reflected in it as if in a great mirror. “Look at that!” exclaimed Thorndyke, pointing down into the depths, “what can that be?” Johnston followed Thorndyke's finger with his eyes. At first he thought that it was a comet moving across the sky and reflected in the water; but, on glancing above, he saw his mistake. It looked, at first, like a great ball of fire rolling along the bottom of the lake with a stream of flame in its wake. Chapter II. The two men watched it for several minutes; all the time it seemed to be growing larger and brighter till, after a while, they saw that the light came from something shaped like a ship, sharp at both ends, and covered with oval glass. As it slowly rose to the surface they saw that it contained five or six men, sitting in easy chairs and reclining on luxurious divans. One of them sat at a sort of pilot-wheel and was directing the course of the strange craft, which was moving as gracefully as a great fish. Then the young men saw the man at the pilot-wheel raise his hand, and from the water came the musical notes of a great bell. The vessel stopped, and one of the men sprang up and raised an instrument that looked like a telescope to his eyes. With this he seemed to be closely searching the lake shores, for he did not move for several minutes. Then he lowered the instrument, and when the bell had rung again, the vessel rose slowly and perpendicularly to the surface and glided to the shore within twenty yards of where the adventurers stood. “Could they have seen us?” whispered Thorndyke, drawing Johnston nearer the side of the cliff. “I think so; at all events, they are between us and the outlet; we may as well make the best of it.”