"All hands follow me. There's no danger," called the guide, shouldering his pack and leaping and sliding down the sharp incline. He was followed by the boys with shouts of glee. They went tumbling head over heels, laughing, whooping, letting off their excess steam. The Professor's grim face relaxed in a smile; Dad's eyes twinkled.
"We'll take it out of them by and by," he confided to the Professor.
"You don't know them," answered Professor Zepplin. "Better men than you or I have tried it. Remember, they are young. We are old men. Of course, it is different with you. You are hardened to the work, still I think they could tire both of us out."
"We'll see about that."
"Whoop-e-e!" came the voice of Tad Butler far below them. "I'm at the bottom. Any wild animals down here, Dad?"
"Only one at present. There'll be three more in a minute."
"Six, you mean," laughed Tad.
The others had soon joined him.
"How far are we from the surface?" asked Walter.
"About five hundred feet down. We're in the bowels of the mountain for sure, kid," answered the guide.