The Irishman, somehow or other, had formed the idea that the outlet of the water would show them a way of getting out of the cavern.  Despite his careless and indifferent disposition, he showed considerable anxiety, as he led the way along the bank, holding the smoking torch far above his head, and lighting up the gloom and darkness for a long distance on every hand.

“When your eye rists on anything interesting, call me attention to the same,” he cautioned him.

“I’ll be sure to do that,” replied Fred, who let nothing escape him.

The scenery was gloomy and oppressive, but acquired a certain monotony as they advanced.  The dark water, throwing back the light of the torch; the towering, massive rocks overhead and on every hand; the jagged, irregular roof and floor—­these were the characteristics of the scene which was continually opening before and closing behind them.  In several places the brook spread out into a slowly flowing pond of fifty or a hundred feet in width; but it maintained its progress all the time.

At no point which they examined did the depth of the water appear greater than three feet, while in most places it was less than that.  It preserved its crystal-like clearness at all times, and in all respects was a beautiful stream.

When they had advanced a hundred yards or so, the camp-fire which they had left behind them took on a strange and unnatural appearance.  It seemed far away and burned with a pale yellow glare that would have seemed supernatural, had it been contemplated by any one of a superstitious turn.

As near as Mickey could estimate, they had gone over a hundred and fifty yards when the point was reached where the stream gathered itself and passed from view.  Its width was no greater than four feet, while its rapidity was correspondingly increased.

After Mickey had contemplated it awhile by the light of the torch, he handed the latter to Fred, and told him to go off so far that he would be left in total darkness.  This being done, the man set to work to study out the problem before him.

His theory was that, if the passage of the stream from the cavern to the outside world were brief, the evidence of it could be seen, perhaps, in the faintest tinge of light in the water, The sun was shining brightly on the outside. and unless the stream flowed quite a distance under ground, a portion of the refracted light would reach his eye.

Mickey peered at the base of the rock for a few minutes, and then exclaimed, with considerable excitement: 

“Be the powers! but it’s there!”

It was dim and faint, as light is sometimes seen through a translucent substance, but he saw it so plainly that there could be no error.  When he looked aloft at the impenetrable gloom, he was sensible of the same dim light upon the water.  He tested his accuracy of vision by looking in different directions, but the result was the same every time.