We stared at the stone in silence.  The top was covered with short moss that had gathered there through the centuries, and instead of being flat as we had surmised there was a noticeable slope, so that the part that was directly behind the camp was fully two feet higher than the rear.  This was the only peculiarity in its construction, and although we sat in silence, staring at its moss-covered surface, we were utterly unable to put forward the slightest supposition that would account for the disappearance of the watcher.  The incident was an extraordinary one.  The man could not have dropped from the table before we reached the supporting piers, and we were equally certain that he had not slipped down the pillars while we stood guard beneath.

“I’m going up there,” muttered Holman.  “We can get the rope from the camp.  Come along!  I’d like a look at that place at closer quarters.”

We climbed hastily down the tree, crept cautiously back to the camp and took the stout rope which we had used in reaching the Ledge of Death.  The camp was quiet.  The curious nasal sounds produced by the natives, together with the rather high-toned snore of Professor Herndon, were the only sounds that came through the still night.

Holman flung one end of the rope over a projecting corner of the flat slab, twisted one half of it round and round the pillar to make occasional grips which we could use in the ascent, then clutching the hanging end he worked himself slowly up.  I followed him, only to find the upper surface of the table as bare of any signs of life as we had previously noted from our perch in the chestnut tree.  The tough moss upon the stone was fully four inches long, and covered the slab completely.  In vain we stamped around looking for a possible hiding place.  The massive block didn’t offer a cranny that a lizard could hide in, and with an unsolved mystery upon our hands we descended to the ground.

“What do you make of it?” asked Holman.

I shook my head.  The enigma baffled me.  Our suspicions regarding the honesty of Leith made the strange appearance of the figure on the table of stone more perplexing than it would have been under ordinary circumstances.  Leith had asserted that the island was uninhabited, yet we were not inclined to rush to him with the news of the discovery.  We felt that it was another of the small discoveries that made us pile up suspicions against the big bully at the head of the party.  We had no proof of the midnight visitor, and the story of his sudden disappearance while we watched below would only provoke an unbelieving grin from Leith, and an idiotic laugh from the foolish old Professor.

“Better keep it to ourselves,” growled Holman.

“For the present at any rate,” I remarked.  “If Leith knows that there are others upon the island, and if those others are friendly to him, it will only make him more careful of his actions if we tell what we have seen to-night.”