The fact was, a cave had originally occupied the spot and the galleries and passages had been added by man. It was certainly a wonderful spectacle. The floor was full fifty feet below, and as our adventurers looked down from the gallery they saw a large number of the greasers lounging about the place. Many were rolled in blankets and sound asleep. Others were playing dice or talking and smoking their cheroots, and the hum of conversation came upon the air. “By Jove!” exclaimed Frank, with a thrill, “I tell you, Barney, we have found the den of Costello and his gang.” “Begorra, that’s thrue,” agreed Barney. “It is certainly a place well suited for the purpose.” “I should say so, sor. But however will we get out of here?” “That is a question.” “Shure, sor, I think we’d betther get out as soon as possible.” “Right you are, Barney. If those miners return and discover our escape from the shaft they will be quickly after us.” “Shure enough, sor.” “Let us move cautiously along and see where this gallery goes to.” Frank led the way along the gallery. It terminated in a flight of steps cut in solid rock. There were none of the greasers, apparently, in any of the galleries or passages above the floor. So Frank felt safe in descending these steps. He went down them until a gallery below was reached. They were now quite near to the floor. Frank and Barney here paused. It was, of course, decidedly unsafe to venture down within the circle of the firelight. “If they would only all go to sleep,” said the young inventor, “then we could be sure of slipping by them.” But the greasers seemed to have no such idea in view. There was no doubt but that many of them would remain up all night. What was to be done? Frank pondered the question seriously and long. He saw what he believed was the passage which led out of the mine. But men were constantly passing in and out, and it would be utterly impossible to escape in that direction. Meanwhile, the risk was great in staying where they were. At any moment some one of the greasers might come upon them. It was clear that desperate action had got to be taken at once. Frank considered every daring move which he could think of. He even thought of a break for liberty through the outer passage. But second thought showed that this was suicidal. But he noted that there was a line of shadow under the galleries. Perhaps by keeping in this he could find another outward passage. It was a terrible risk to take, but Frank did not hesitate. “Come, Barney!” he said, “let us go down below.” The Celt, without a word, followed Frank. But they had not descended three steps when the young inventor came to a startled halt. A thrilled exclamation escaped his lips. CHAPTER XII. THE PURSUIT UNDERGROUND. “Heavens!” he gasped. “We cannot go down now. Back for your life, Barney.” The Celt, who would have followed his master anywhere, obeyed this command.