All divers practice this art, for possible use should anything become the matter with their diving outfits while at work. He felt in his clothing and found his water-proof matchbox still safe. Soon he had a tiny light, and seeing some dry driftwood at hand he set it on fire. The blaze threw grotesque shadows on the rocky walls around him, but revealed nothing to his gaze but those same walls and the silent, underground stream flowing between them. He was entombed alive! Gradually this conviction forced itself upon him, causing him to shiver as if with the ague. Again he called out the name of his late companion, and again only the dull echoes answered him. He reckoned that he must be at least a hundred yards from the hole made by the sunken driftwood. To get back to the hole, therefore, was out of the question. He thought the matter over for a while, and then, taking up some driftwood for a torch, walked slowly along the sandy shore of the black stream. Presently he came to a bend, and here found that the stream shot downward, forming an underground waterfall. "I can't go in that direction," he reasoned. "I want to go up, not down." The stream was less than twelve feet wide, and did not run so swiftly but what he could cross it without much danger. Obtaining a fresh firebrand, for the first was now burnt out, he swam over to the opposite shore and began an investigation on that side. "Hurrah!" The exclamation escaped from his lips involuntarily. The firebrand had dropped from his hand into the stream, leaving him in darkness. Looking at the rocks, he had beheld a thin shaft of light striking down from some opening above. "An opening! May it prove a way of escape!" With a prayer for aid on his lips, Dave began to climb the rocks as best he could until he reached a hollow ten feet above the stream. Here the light was stronger, and by applying his eyes to a long, narrow slit in the rocks he made out a broad cave beyond, the further end of which was wide open to the sunlight. But how was he to get into the cave? The opening was not over six inches wide, too narrow for the passage of his body. The rocks were large, weighing several hundreds of pounds apiece. To move them would take tools, and he had nothing. Again in a state bordering on despair, he sat down to review his situation. At last he leaped up, and clenching his hands, cried loudly: "I must get out! I simply must!" The cry was an inspiration, for, getting on his knees, he felt around and found that two of the big rocks were unsteady upon their resting places. He pulled away at the smaller stones beneath, and soon had them loosened. He continued his labors, and presently, with a mighty crash, one of the rocks slid down into the stream, disappearing beneath the surface with a splash. At once the light from beyond shot into the opening. He was free! His heart gave a bound of joy, and quickly he scrambled through the hole and into the cave beyond.