As before, the grumbling began with an earth tremor. It was as though some giant, whose mighty limbs were shackled, was trying to break loose; and in so doing made things near him tremble.
Rapidly the noise increased, until it became terrifying. Bob had dropped flat, and cowered there, almost holding his breath with awe. Not so Frank, in whose care was the burning torch.
He had whipped off his coat at the first sign of the disturbance. This he hastily arranged so as to partially protect the burning brand. Of course in such a violent draught the suction was enough to make the flame flare and flicker until at one time Frank feared it could not stand the struggle. But just as he was ready to give up the attempt, the furious wind seemed to slacken.
Bob raised his head to see the torch still burning, and it soon recovered its full capacity for illumination.
"Bully!" he exclaimed, beginning to rise from his position of hugging the rocky floor of the cave; "you did it that time, Frank. But hurry up, and get your coat on. Gee! but this air feels chilly in here, and damp too!"
Frank had found that out for himself. He was even shivering; and made haste to don his jacket.
"Now let's be moving while we have the chance," he said. "I hope that before the next rush comes we'll sight what we're looking for."
Perhaps his sharp eyes had discovered certain signs that told him they were near the working part of the cave. Men cannot mine a lode of precious ore without leaving many traces behind to tell of their presence. And the stream of clear water that passed across the place seemed to offer a splendid chance for panning any golden treasure that might be found in the shape of soft quartz.
Now and again Frank would place the torch behind him. Bob wondered what he did this for until he saw his chum bending his head forward as though endeavoring to discover what lay ahead. Then he realized that the light blinded him while it was before his eyes, and he sought to avoid the trouble in this way.
"There's another bend ahead, Bob," Frank remarked, presently.