observation."

He darted across to the big Pacific chestnut and climbed hurriedly,
while I walked round and round the square pillars and strained my ears
for the slightest sound that would give a hint that the person on the
roof of the mysterious table was preparing to descend.

A low whistle from Holman pierced the silence, and I answered.

"Come up here," he cried softly. "He's given us the slip."

I climbed the tree to the branch where the young fellow sat awaiting me.
From his position he had a clear view of the top of the big table, and
as I reached him I looked through an opening in the thick leaves. The
top of the stone was empty!

"Do you think he slipped down while I was climbing the tree?" asked
Holman.

"I'm certain he didn't," I answered. "It would have been impossible."

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