"You mean it?"

"Of course I mean it."

"I guess I can walk. I'm not quite so big a baby as that."

"I thought so. Have your fun. If you get into trouble you know your friend, Tad Butler, is always on the job."

"You bet I do. But this is an awful climb."

It was all of that. One step upward often meant a slide of several short steps backward. The Professor's face was red, and unuttered words were upon his lips. Jim Nance was grinning broadly, his whiskers bobbing up and down as he stumbled up the side of Old Sunset.

"I reckon the tenderfeet will get enough of it before they get to the Canyon," chuckled the guide.

"Say, Mr. Nance, we don't want to Mister you all the time. What shall we call you for short?" asked Tad Butler.

"Anything you want."

"What d'ye say if we call you Whiskers?" called Stacy.

"Stacy!" rebuked the Professor sternly.

"Oh, let the little tenderfoot rant. He's harmless. Call me Whiskers, if it does ye any good."

"I'm no tenderfoot," protested Chunky.

"Nor be I all whiskers," returned the guide, whereat Chunky's face turned red.

"I guess we'll call you Dad, for you'll have to be our dad for some time to come," decided Tad.

"That'll be all right, providing it suits the fat little tenderfoot."

Stacy did not reply to this. He was having too much trouble to keep right side up just then to give heed to anything else.

"Go zig-zag. You'll never get to the top this way," called Tad. "You know how a switchback railroad works? Well, go as nearly like a switch-back as possible."

"That's a good idea," agreed Dad. "You'll get there quicker, as the young gentleman says."

Tad looked at his companions, grinning broadly. As they got nearer to the top the color of the cinders changed from black to a brick red.

They began to understand why the peak of Sunset always presented such a rosy appearance. It was due to the tint of the cinders that had been thrown from the mouth of the volcano ages ago.

"We have now entered the region of perpetual sunset," announced the Professor.

Chunky took advantage of the brief halt to sit down. He slid back several feet on the treacherous footing.

Still further up the mountain took on a rich yellow color, but near the rim it was almost white. It was a wonderful effect and caused the Pony Riders to gaze in awe. But darkness was approaching rapidly. The guide ordered them to be on the way, because he desired to reach the rim of the crater while they still were able to see. What his reasons were the boys did not know. They took for granted that Dad knew his business, which Dad did. He had spent many years in this rough country and knew it well. The Grand Canyon was his home. He lived in it the greater part of the year. When winter came, Dad, with his mustang, his cattle and equipment would descend into the Grand Canyon far from snow and bitter cold into a land of perpetual summer, where, beside the roaring Colorado, he would spend the winter alone with his beloved Canyon.

Dad's was a strange nature. He understood the moods of the great gash in the plateau; he seemed literally to be able to translate the mysterious moans and whispers of the wind as it swirled between the rocky walls and went shrieking up the painted sides of the gulches.

But of all this the boys knew nothing as yet. It was all to be revealed to them later.

"You'll have a look over the country tomorrow," said Dad.

"Where is the Canyon?" asked Tad, eager for a view of the wonderful spot.

"You'll get a glimpse of it in the morning. You'll know the place when you get to it. Here we be at the top. There's the hole."

Chunky peered into the crater rather timidly.

"How do you get down?" he asked.

"Slide," answered Ned.

"I can do that, but what's at the bottom?"

"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."