At times the passage broadened out until the wall on either side was barely visible, only to narrow down again till it was scarcely more than a crevice between the giant boulders.  The variation of the incline was no less, being at times very nearly level, and at others mounting upward at an angle whose ascent was all but impossible.  Somehow we crawled up, like flies on a wall.

When we came to a stream of water rushing directly across our path at the foot of a towering rock Harry gave a cry of joy and ran forward.  I had not known until then how badly his knee was hurt, and when I came up to where he was bathing it in the stream and saw how black and swollen it was, I insisted that he give it a rest.  But he absolutely refused, and after we had quenched our thirst and gotten an easy breath or two we struggled to our feet and on.

After another hour of scrambling and failing and hanging on by our finger nails, the way began to be easier.  We came to level, clear stretches with only an occasional boulder or ravine, and the rock became less cruel to our bleeding feet.  The relief came almost too late, for by that time every movement was painful, and we made but slow progress.

Soon we faced another difficulty when we came to a point where a split in the passage showed a lane on either side.  One led straight ahead; the other branched off to the right.  They were very similar, but somehow the one on the right looked more promising to us, and we took it.

We had followed this but a short distance when it broadened out to such an extent that the walls on either side could be seen but dimly.  It still sloped upward, but at a very slight angle, and we had little difficulty in making our way.  Another half-hour and it narrowed down again to a mere lane.

We were proceeding at a fairly rapid gait, keeping our eyes strained ahead, when there appeared an opening in the right wall at a distance of a hundred feet or so.  Not having seen or heard anything to recommend caution, we advanced without slackening our pace until we had reached it.

I said aloud to Harry, “Probably a cross-passage,” and then jerked him back quickly against the opposite wall as I saw the real nature of the opening.

It led to a small room, with a low ceiling and rough walls, dark as the passage in which we stood, for it contained no light.

We could see its interior dimly, but well enough to discover the form of an Inca standing just within the doorway.  His back was toward us, and he appeared to be fastening something to the ceiling with strips of hide.

It was evident that we had not been seen, and I started to move on, grasping Harry’s arm.  It was then that I became aware of the fact that the wall leading away in front of us—­that is, the one on the right—­was marked as far as the eye could reach with a succession of similar openings.

They were quite close together; from where we stood I could see thirty or forty of them.  I guessed that they, too, led to rooms similar to the one in front of us, probably likewise occupied; but it was necessary to go on in spite of the danger, and I pulled again at Harry’s arm.