Through the air, over the heads of Rick, Chot and Ruddy, now seemingly on one side and now on the other—surrounding them, as it were—the mysterious noise came and went. Now it almost died away—an expiring groan¹ it might be from some unseen inhabitant of the tunnel. Then again, it would fairly howl around them. And at the conclusion of one of these weird² howls Ruddy again joined his voice to that of the unseen one, making so nerve-racking a combination of notes as to cause cold shivers to run down the spines³ of the lads.  
“Whew!” whistled Chot, as the sound seemed to vanish into the mysterious black recesses⁴ of the place, “this is too much for me!”
 
“You’re not going to quit; are you?” cried Rick, for he saw the light of Chot’s lantern drawing away.
 
“Why not?” demanded Chot. “This is fierce! You aren’t going to stay; are you?”
 
“I’m going to stay and I’m going on!” declared Rick firmly.
 
“Well,” went on Chot, “I’m not going to desert, but when Ruddy howls like he did—that’s enough. There’s something unhuman here, Rick.”
 
“It doesn’t sound very pleasant,” admitted the boy. “There it comes again!” he cried, as, once more, the mysterious noise filled the black tunnel, which the lanterns of the boys seemed to make only the darker.
 
Around them, above them, on all sides of the lads circulated that weird sighing, howling, groaning⁵ and yelling noise, as though hundreds of imps⁶ of blackness were calling to each other in the gloom, laughing in fiendish glee at the plight⁷ of the boys.
 
Ruddy once more howled dismally⁸, ending with such a queer note of protest in his voice that, in spite of his fears, Rick laughed.
 
“What’s the matter, old fellow?” he asked, as he patted the dog’s head. “Can’t you stand a little groaning?”
 
“If we only knew what it was,” spoke⁹ Chot in rather a chattering¹⁰ voice. “Do you reckon that’s just the wind making echoes in here, Rick?”
 
“First I thought it was the wind, maybe blowing through holes in the rocks,” said Rick. “I remember reading in the book ‘Tom Brown’s Schooldays’ how there was a ‘blowing stone’ as it was called. A man in an inn blew through a hole in the stone back of the fireplace and the sound came out of a hill half a mile off. I thought maybe it was like that here, but there’s no wind.”
 
“No,” agreed Chot, “or, anyhow, there isn’t enough wind to make all those howls. It blows a little, but not enough for that.”
 
The boys, as I have told you, noticed a wind blowing toward them through the tunnel as soon as they opened the closed end by removing the barrier stones. And after entering the black horizontal shaft¹¹ they had been aware of a constant current of air in their faces, showing that there was an opening at the farther end which they had not yet reached. But, as Chot remarked, there was not enough of the wind, or air current, to account for the noises.
 
“If the wind made it,” said Chot, “we’d feel a sudden breeze as soon as the sound came.”
 
“That’s right,” agreed Rick.
 
Again echoed the howls and wails¹², like those of the fabled¹³ banshee of Ireland, but the boys only felt the same gentle air currents in their faces.
 
“It might be there is a current of air higher up, away over our heads, that we don’t feel,” suggested Chot. “That might cause it.”
 
“We’ll see,” said Rick. He carried a long pole, and on the end of this he put the handle of an oil lantern, raising the light as high as he could toward the roof. “If there’s a current there it will flicker¹⁴ the light,” Rick told his chum.
 
The two boys watched the lantern. It’s flame burned as steadily^{15............}