"Remember, Nick has the best of the jewels," went on Merwell, rather spitefully.
"I am not likely to forget it," answered Dave, grimly. "Now, the sooner we get out of this hole the better."
Merwell was just as anxious to see daylight, even if he was to be held a prisoner, and together the boys hunted around for some exit from the underground watercourse. But the only way out seemed to be far overhead, and to climb up the smooth, sloping rocks proved impossible.
"Oh, what shall we do?" groaned Merwell, after they had attempted to climb up and had failed. "We are caught like rats in a trap!"
"Perhaps we'll have to swim for it," answered Dave. "This water is very salt, which proves it comes from the ocean. Moreover, it is gradually going down, showing it is affected by the tide. Let us follow the stream for a short distance and see where it leads to."
Merwell demurred, but he did not want to remain behind alone in the semi-darkness, so he followed Dave, and both waded and swam a distance of several hundred feet. Here the underground river made a turn around the rocks, and both boys were delighted to see a streak of sunlight resting on the water.
"An opening of some sort!" cried our hero.
