On and on they went, the darkness illuminated only by the torches they carried. But they noticed that the air was still fresh, and that a gentle wind blew toward them. The passage was undoubtedly artificial, a tunnel made by the hands of men now long crumbled into dust. It had a slightly upward slope, and this, Professor Bumper said, indicated that it was bored upward and perhaps into the very heart of the mountain somewhere in the interior of which was the Beecher party.
Just how far they went they did not know, but it must have been more than two miles. Yet they did not tire, for the way was smooth.
Suddenly Tom, who, with Professor Bumper, was in the lead, uttered a cry, as he held his torch above his head and flashed it about in a circle.
"We're blocked!" he exclaimed. "We're up against a stone wall!"
It was but too true. Confronting them, and extending from side to side across the passage and from roof to floor, was a great rough stone. Immense and solid it seemed when they pushed on it in vain.
"Nothing short of dynamite will move that," said Ned in despair. "This is a blind lead. We'll have to go back."
"But there must be something on the other side of that stone," cried Tom. "See, it is pierced with holes, and through them comes a current of air. If we could only move the stone!"
"I believe it is an ancient door," remarked Professor Bumper.
Eagerly and frantically they tried to move it by their combined weight. The stone did not give the fraction of the breadth of a hair.
"We'll have to go back and get some of your big tunnel blasting powder, Tom," suggested Ned.