"Suppose we take a walk all round on the beach," proposed the Englishman; "there is no telling what we may find; we may run on something that has drifted ashore from some wrecked ship."Johnston consented. They had encompassed the entire island, which was oval in shape, and were about to ascend to the rock to put fresh fuel on the fire before lying down to sleep for the night, when Thorndyke noticed a road that had evidently been worn in the rock by human footsteps.

"Made by feet," he said, bending down and looking closely at the rock and raking up a handful of white sand, "but whether the feet of savage or civilized mortal I can't make out."Johnston was a few yards ahead of him and stooped to pick up something glittering in the moonlight. It was a tap from the heel of a shoe and was of solid silver.

"Civilized," he said, holding it out to his companion; "and of the very highest order of civilization. Whoever heard of people rich enough to wear silver heel-taps.""Are you sure it is silver?" asked the Englishman, examining it closely.

"Pure and unalloyed; see how the stone has cut into it, and feel its weight.""You are right, I believe," returned Thorndyke, as Johnston put the strange trophy into his pocket-book, and the two adventurers paused a moment and looked mutely into each other's eyes.

"We haven't the faintest idea of where we are," said Johnston, his tone showing that he was becoming more despondent. "We don't know how long we were unconscious in the balloon, nor where we were taken in the storm. We may now be in the very centre of the North Polar sea--this knob may be the very pivot on which this end of the earth revolves."The Englishman laughed. "No danger; the sun is too natural.

>From the poles it would look different."

"I don't mean the old sun that you read so much about, and that they make so much racket over at home, but another of which we are the original discoverer--a sun that isn't in old Sol's beat at all, but one that revolves round the earth from north to south and dips in once a day at the north and the south poles. See?"The Englishman laughed heartily and slapped his friend on the shoulder.

"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.