I took the slip of bark to the firelight and we examined it together. It was about a foot square, and on the inner side there was a singular arrangement of lines, which I here reproduce:
They were neatly done in charcoal upon the white surface, and looked to me at first sight like some sort of rough musical score.
“Whatever it is, I can swear that it is of importance to us,” said I. “I could read that on his face as he gave it.”
“Unless we have come upon a primitive practical joker,” Summerlee suggested, “which I should think would be one of the most elementary developments of man.”
“It is clearly some sort of script,” said Challenger.
“Looks like a guinea puzzle competition,” remarked Lord John, craning his neck to have a look at it. Then suddenly he stretched out his hand and seized the puzzle.
“By George!” he cried, “I believe I’ve got it. The boy guessed right the very first time. See here! How many marks are on that paper? Eighteen. Well, if you come to think of it there are eighteen cave openings on the hillside above us.”
“He pointed up to the caves when he gave it to me,” said I.
“Well, that settles it. This is a chart of the caves. What! Eighteen of them all in a row, some short, some deep, some branching, same as we saw them. It’s a map, and here’s a cross on it. What’s the cross for? It is placed to mark one that is much deeper than the others.”
“One that goes through,” I cried.
“I believe our young friend has read the riddle,” said Challenger. “If the cave does not go through I do not understand why this person, who has every reason to mean us well, should have drawn our attention to it. But if it does go through and comes out at the corresponding point on the other side, we should not have more than a hundred feet to descend.”
“A hundred feet!” grumbled Summerlee.
“Well, our rope is still more than a hundred feet long,” I cried. “Surely we could get down.”
“How about the Indians in the cave?” Summerlee objected.
“There are no Indians in any of the caves above our heads,” said I. “They are all used as barns and storehouses. Why should we not go up now at once and spy out the land?”
There is a dry bituminous wood upon the plateau—a species of araucaria, according to our botanist—which is always used by the Indians for torches. Each of us picked up a faggot of this, and we made our way up weed-covered steps to the particular cave which was marked in the drawing. It was, as I had said, empty, save for a great number of enormous bats, which flapped round our heads as we advanced into it. As we had no desire to draw the attention of the Indians to our proceedings, we stumbled along in the dark until we had gone round several curves and penetrated a considerable distance into the cavern. Then, at last, we lit our torches. It was a beautiful dry tunnel with smooth gray walls covered with native symbols, a curved roof which arched over our heads, and white glistening sand beneath our feet. We hurried eagerly along it until, with a deep groan of bitter disappointment, we were brought to a halt. A sheer wall of rock had appeared before us, with no chink through which a mouse could have slipped. There was no escape for us there.
We stood with bitter hearts staring at this unexpected obstacle. It was not the result of any convulsion, as in the case of the ascending tunnel. The end wall was exactly like the side ones. It was, and had always been, a cul-de-sac.
“Never mind, my friends,” said the indomitable Challenger. “You have still my firm promise of a balloon.”
Summerlee groaned.
“Can we be in the wrong cave?” I suggested.
“No use, young fellah,” said Lord John, with his finger on the chart. “Seventeen from the right and second from the left. This is the cave sure enough.”
I looked at the mark to which his finger pointed, and I gave a sudden cry of joy.
“I believe I have it! Follow me! Follow me!”
I hurried back along the way we had come, my torch in my hand. “Here,” said I, pointing to some matches upon the ground, “is where we lit up.”
“Exactly.”
“Well, it is marked as a forked cave, and in the darkness we passed the fork before the torches were lit. On the right side as we go out we should find the longer arm.”
It was as I had said. We had not gone thirty yards before a great black opening loomed in the wall. We turned into it to find that we were in a much larger passage than before. Along it we hurried in breathless impatience for many hundreds of yards. Then, suddenly, in the black darkness of the arch in front of us we saw a gleam
