“The same thing.  Cinders and lava,” answered Tad.  “What would you expect to find in a volcano?”

“I’d never expect to find Stacy Brown in one, and I’m not sure that I’m going to.”

“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.

“That’s pretty tough on the mountain.  I’m afraid it will have a bad case of indigestion,” laughed Tad.

“You needn’t be.  It has swallowed tougher mouthfuls than you are,” returned the guide, ever ready with an answer.

“Dad’s able to give as good as you send,” laughed Ned.

“That’s good.  All the better for us,” nodded Tad.  “What about some light?”

“Unload the wood from your packs.  This is where you are glad you did pack some stuff.”

In a few minutes a fire was blazing, lighting up the interior of the crater.  The boys found themselves in a circular opening of almost terrifying roughness and something like a quarter of a mile across.  Here, in ages past, the forces of Nature had been at work with fearful earnestness.  Weird shadows, mysterious shapes, somewhat resembling moving figures, were thrown by the flickering blaze of the camp fire.  While the boys were exploring the crater Dad was busy getting the supper ready, talking with Professor Zepplin as he worked.

The voices of the boys echoed from side to side of the crater, sounding strange and unreal.  The call to supper put an end to their explorations.  They sat down with keen edges to their appetites.  It was their first meal in the open on this journey.  All were in high spirits.

“I think we should agree upon our work for the future,” declared the Professor.

“Work?” exclaimed Chunky, opening wide his big eyes.

“Yes.  It is not going to be all play during this trip.”

“We are willing to do our share,” answered Ned.