“How do you know it is the south?” asked Percival.
“Because the trees are more worn on this side, from frost and exposure. Look on the other side and you will see a difference.”
“Yes, I see it. The other side is smooth, while this is rough and of a different color. And that is the north side, is it? I have noticed trees looking like that, but did not think of settling direction by it.”
“Yes, you can, and you will never go wrong. Come on, I think we can find the boys all right,” and with a look at the sun, which could be seen above the treetops, Jack started off, Percival following.
Jack knew from the position of the sun and from the exposed side of the trees which way to go, and he pushed on in a straight line without deviating a foot to either side toward where he judged he would find the boys, keeping an eye for ledge rock and listening for any sounds which would tell him that he was nearing the other end of the cave.
In the meantime, unknown to the two chums, the boys remaining at the gully were having a bit of excitement of their own, and were seriously alarmed about the two in the cave.
The sound that Dick and Jack had heard in the cave was not thunder, as Jack had suggested, but something entirely different.
When the boys had been in the cave a short time, there came a sudden rustling on a part of the ledge Billy had aimed his camera at, and all of a sudden a great boulder fell into the gully.
“Hello!” exclaimed Arthur. “That’s bad. Who would have thought of it? Jack and Dick are shut in there!”
A considerable mass of earth had been carried down with the boulder, and now the entrance to the cave was completely filled by the rubbish.