The youngster’s eyes opened as he looked again at the circular pit with its brilliantly tinted sides.  The answer perplexed him, and he waited anxiously for an explanation.

“But how can we?” he asked.

Leith stood for a moment before replying, then he moved closer to the edge of the crater and pointed down.

“The road is directly beneath you,” he remarked.  “If you come closer to the edge you can see it.”  Holman glanced at me in amazement, and moved by the one impulse we stepped toward the ledge.  The rim of the vast pit, at the point where Leith was standing, was composed of porphyry of a dark-green shade, and as we neared the edge we noticed that this had been worn to that peculiar velvety smoothness that one notices on the pillars of Indian temples, where the sweaty hands of millions of worshippers have helped in the polishing process through unnumbered centuries.

Leith noticed that our glances were directed upon the peculiar polished portion of the rim, and his grin broadened.

“You won’t be the first to go over on to the track below,” he drawled.  “If I had a dollar for every man who slipped over here since the world began I wouldn’t bother with specimens for American and European museums.  See, the ledge is directly beneath, and it leads away to the right.”

We stretched out our necks and looked, and I tried to thrust back the exclamation that came to my lips.  Directly beneath the polished part of the rim, and about four feet below it, was a ledge barely three feet wide, and this narrow path wound away to the right and disappeared through a cavernous opening in the brightly tinted walls of the crater.  The ledge was bare and unprotected, polished to the same velvety smoothness as the spot on the rim near which we stood, and when one looked at it and then let his eyes glance over the infernal depths that were immediately beneath, the brain reeled with thoughts of the danger to which a climber would be exposed while making his way along it to the cavern in the wall.

Holman took a great breath of air and turned savagely upon Leith.

“What sort of a fool game are you up to?” he cried.  “What do you mean?”

Leith’s lower jaw came forward menacingly.  “You had better hold your tongue!” he roared.  “If you don’t I’ll—­I’ll——­”

He stopped and glared at the young fellow, a murderous expression creeping over his sallow face.  The half-voiced objection to the route had stirred all the sleeping devil in him, and the big stubby fingers crooked as if certain they would be called upon to grip Holman’s throat.

“You’ll do what?” asked the youngster coolly.

“I’ll bundle you back to the yacht!” screamed the giant.  “You’ve been allowed to come on this trip through the good nature of Professor Herndon, but you mustn’t think you have any voice in the direction of affairs.”

Holman did not reply.  The dangers of the path over which it was evident that Leith intended to take us dazed him, and he looked at me as if asking confirmation of his opinions.