The next minute the boys felt a great billow of wind coming toward them and a queer rushing sound as of a great river flowing between rocks. Frank’s candle was blown out instantly and they were enveloped in total darkness.
Frank and Harry felt their faces beaten against by countless leathern wings and Billy was fairly knocked over by the onslaught,—which had scared him not a little. It was all over as quickly as it had begun almost.
“Jimminy crickets, what on earth was that?” demanded Billy, picking himself up.
“Bats,” laughed Frank, “no wonder they were in a hurry to get out. They must have been imprisoned in here since last that stone swung into place.”
“I hope they’ve all taken their walking, or rather flying papers,” commented Billy, sputtering and coughing as were the other boys from the terrific dust the creatures had fanned up with their wings, “anything more like that would get on my nerves.”
Frank soon had his candle relit and they resumed their descent. The stairway did not continue very much further, however. When they had reached a point which Frank estimated must have been back underground about half a mile from the face of the cliff their feet suddenly encountered a hard level floor. It was a welcome change from the monotonous downhill march.
“We have a few tons of mountain on top of us now,” remarked Harry, who had also taken careful note of the direction the stairway followed.
“Yes,” agreed Frank, who had verified his guess of the direction in which they had been proceeding by his compass. “Just think of the work those fellows—or rather their slaves—accomplished when they dug this tunnel through solid rock without powder or dynamite, so far as we know.”
“It must have been well traveled,” exclaimed Harry, “look here.” He called his brother’s attention to the narrow walls of the stairway by which they had descended. They were grooved on each side, at a height of about three and a half feet, with a smooth, worn, shallow sort of trench.
“What did that, do you suppose?” asked Billy.