“They may have an hour’s start of us,” came Harry’s voice at my side.

“Or five minutes,” I returned.  “We have no way of knowing.  But I’m afraid we’re on the wrong trail.”

Still as I had said, one chance was as good as another, and we did not slacken our pace.  The passage went straight forward, without a bend.  The roof was low, just allowing us to pass without stooping, and the walls were rough and rugged.

It was not long before we found that we had taken the wrong chance, having covered, I think, some two or three miles when a wall loomed up directly in our path.

“At last, a turn!” panted Harry.

But it was not a turn.  It was the end of the passage.  We had been following a blind alley.

Harry let out a string of oaths, and I seconded him.  Twenty minutes wasted, and another twenty to return!

There was nothing else for it.  We shouldered our spears and started to retrace our steps.

“No use running now,” I declared.  “We can’t keep it up forever, and we may as well save our strength.  We’ll never catch up with ’em, but we may find ’em.”

Harry, striding ahead two or three paces in front, did not answer.

Finally we reached the cavern from which we had started.

“And now what?” asked Harry in a tone of the most utter dejection.

I pointed to the exit in the middle.  “That!  We should have taken it in the first place.  On the raft we probably descended altogether something like five hundred feet from the level where we started—­possibly twice that distance.  And this passage which slopes upward will probably take us back.”

“At least, it’s as good as the other,” Harry agreed; and we entered it.

We had not proceeded far before we found ourselves in difficulties.  The gentle slope became a steep incline.  Great rocks loomed up in our path.

In spots the passage was so narrow that two men could hardly have walked abreast through it, and its walls were rough and irregular, with sharp points projecting unexpectedly into our very faces.

Still we went forward and upward, scrambling over, under, round, between.  At one point, when Harry was a few yards in front of me, he suddenly disappeared from sight as though swallowed by the mountain.

Rushing forward, I saw him scrambling to his feet at the bottom of a chasm some ten feet below.  Luckily he had escaped serious injury, and climbed up on the other side, while I leaped across—­a distance of about six feet.

“They could never have brought her through this,” he declared, rubbing a bruised knee.

“Do you want to go back?” I asked.

But he said that would be useless, and I agreed with him.  So we struggled onward, painfully and laboriously.  The sharp corners of the rocks cut our feet and hands, and I had an ugly bruise on my left shoulder, besides many lesser ones.  Harry’s injured knee caused him to limp and thus further retarded our progress.