A small stone fell in front of the cave. In the silence, broken only by the murmur of the stream and the sighing of the wind in the pines it sounded as startlingly loud as a rifle shot. Presently another fell.
Could it be a signal of some kind?
But suppose it was—who could it be? Certainly not Mr. Chillingworth or the boys’ uncle, or——
At this point of Tom’s meditations another small stone fell. There could no longer be any doubt. Somebody on the cliff above was trying to attract their attention. But there did not seem to be any way of showing him that they heard and understood.
All at once, both boys, who had been painfully wiggling toward the front of the cave—moving with difficulty in their tight bonds—gave a surprised gasp.
Something that at first glance seemed like a strand of spider’s web, with an immense spider hanging on the end of it, was swinging in the cave mouth, between them and the red glow of the dying watch fire.
But it was not a spider, nor a web. It was a thin string, and as Tom struggled to the front of the cave and neared the object dangling at the end of the cord, he almost fell backward with astonishment.
It was an opened clasp-knife.
CHAPTER X.
IN DIRE STRAITS.
Moving with the utmost caution so as not to arouse the sleeping Indian, Tom attempted to reach the knife with his bound hands. But he found this impossible to do. After a dozen efforts he realized that it was hopeless. It began to look as if their unknown benefactor might have striven in vain to aid them. But Tom’s mind was not one to be overcome by an obstacle, however insurmountable it might seem at first blush.