“Shure, I don’t know, sor.” “Well, that is odd!” exclaimed the young inventor, with a laugh, in spite of the possible seriousness of the situation. “How did you get there?” “I don’t know that, sor.” Frank was puzzled. The voice of the Celt seemed to be within a few yards of him, and yet was dull and muffled. It occurred to Frank of a sudden that Barney had wandered into a parallel passage and was now opposite him, beyond a thick wall of stone. Satisfied of this, Frank said: “I thought you were right behind me, Barney.” “Shure, so I was.” “But you are in another passage. You must have deviated back here a ways.” “Very loikely, sor. Pwhat shall I do about it?” “Why, go back, of course, and get into the right passage and come along with me.” “All roight, sor.” “Be sure and take the first turn to the right. Then keep straight along the wall until you reach me.” “Will yez wait, sor?” “Of course I will.” “All roight. Here goes thin.” Frank heard a distant shuffling sound and then all was still. What seemed like an age passed. Barney did not appear. Frank listened in vain for some sound of his approach. All was tomb-like stillness. “Well,” muttered the young inventor, “that is queer.” Finally Frank raised his voice and shouted: “Barney! Where are you?” Again and again he shouted. No answer came back. Now Frank was really alarmed. Cold perspiration burst out upon him. “My soul!” he gasped. “It cannot be that he is lost.” Fearful that this was the case Frank lost no time, but started to retrace his steps. He kept carefully and closely to the wall of the passage and at intervals shouted loudly. But each time no answer came. Only the dull, muffled echoes. It was certainly an alarming matter. Frank did not credit any assumption that Barney had fallen into the hands of the greasers. He reckoned, correctly enough, that the Celt had been misled further away into other passages and was lost. Indeed, the mine was a veritable labyrinth, akin to the fabled one of Crete. Frank was not sure that he would ever find his way out of the place, and was oppressed with dismay. On for some distance he went. It was easy enough to follow the passage wall. It seemed certain that it must sooner or later bring him into the one in which Barney had gone astray. But the darkness was so very thick that any course was rendered deceptive. It was almost impossible to tell, with any degree of certainty, just where any one would come up. For that matter, it would be easy to keep up a perpetual circuit until death from sheer exhaustion should come to end the struggle. It was a situation not without grim terrors. CHAPTER XIII. A STRUGGLE IN THE DARK. The further Frank went along the cavern wall, the more fearful he became that he would not be able to find Barney again. This was most dismaying and the young inventor’s heart sank. But he set his lips firmly.