Finally, urged on by this same enthusiasm, Professor Zepplin ventured in as far as the first chamber one afternoon, and what he found there raised his hopes to the highest pitch.

"I must be careful. I must be cautious. No one must know of my discovery just yet," he breathed, glancing apprehensively about, as he emerged from the cave on hands and knees.

Yet, as he came out, the Professor failed to observe two pairs of eyes that were watching his every movement from the rocks above the entrance to the cave.

Believing himself entirely alone, the Professor spread the ore he had just gathered on the ground before him, taking up each piece of mineral, fondling it and gazing upon it with glowing eyes.

"Gold! Bright yellow gold! A fortune, indeed!"

With a deep sigh of satisfaction, he gathered up the specimens, replacing them in his bag with great care. He drew the mouth of the bag shut, tying it securely.

So thoroughly absorbed was he with his great discovery, that he was all unconscious of the fact that a man had been creeping up to him from the rear while he had been thus engaged.

In one hand the fellow carried a stout stick, the free hand being employed to aid him in his cat-like creeping movements.

"I wonder if anyoue suspects," mused the scientist, sitting with a far-away look in his eyes. "Well, we shall see. We shall----"

The words died on the Professor's lips, as the tough stick, which had been raised above him, was brought down with a resounding whack, squarely on the top of his uncovered head.

Sudden darkness overwhelmed Professor Zepplin. He sank down with a moan, into utter oblivion.

When finally his heavy eyelids had struggled apart, night had fallen. At first, he could not imagine where he was nor what had happened. Shooting pains throbbed through his head and down into his arms and body.

The Professor uttered a suppressed moan, closed his eyes and lay back, vainly groping about in his disordered mind for a solution of the mystery.

Step by step he went back over the occurrences of the afternoon, which gradually became clearer, until at last he reached the point where he had finished his examination of the specimens of ore, in front of the cave entrance.

"And that's where I am now," decided Professor Zepplin, sitting up. "But, what happened then? I have it. Something hit me."

His hand instinctively went to his injured head. Then, with trembling fingers he began searching for the bag of minerals.

It was nowhere to be found. The Professor marveled at this for some minutes.

Like a blow, the answer came to him.

"Robbed!" he exclaimed.

Struggling to his feet, the German staggered down the rocks toward the camp, calling for Jose with the full strength of his voice. The Professor having been a.s.sisted to his tent and a lotion prepared for his aching head, Jose was hurried off to the cabin of Ben Tackers with an urgent demand for his presence.

When Ben responded, and had listened to the full account of Professor Zepplin's mishap, he sat grave and thoughtful.

"Bad lot," he growled. "Ab Durkin's one of the most lawless critters on the Park Range; and I've got all I'm goin' to stand from him. The sheriff will settle him when he gits here----"

"I don't care anything about the sheriff. The coward shall suffer for this, if he is the one who attacked me. I'll drive him out myself, if you won't help me. I'll----"

"I'm with you all right, pardner."

"Then, come. I'm ready now," urged the Professor rising.

"What you going to do?" "I am going back there to take possession of that claim. That's what I am going to do. And it will be worse for the man who tries to stop me," declared Professor Zepplin, taking a revolver from his kit, and examining it to see that all the chambers were loaded. "I'd like to see this man, Ab, attempt to interfere with my rights--I mean, interfere again."

Yet, had he known what was in store for him, the Professor might have hesitated before taking the step that he had determined upon.

CHAPTER XXIII

THE PONY RIDERS UNDER FIRE

With many a whoop and hurrah, the boys dashed into the home camp in the early forenoon of the following day.

Lige had left them three miles down the trail, that he might make a short cut to Eagle Pa.s.s for the purpose of getting word to the parents of the boys, that their trip had been concluded, and asking that directions for their further journeys might be sent to them at Denver, where they were to travel by easy stages.

The trail to camp being clear and easily followed, he felt no apprehension in allowing them to go on alone.

"Halloo the camp!" shouted Ned, hurling his sombrero on high, riding under and deftly catching it as it descended.

"Why, there's no one here!" exclaimed Tad Butler, looking about inquiringly, as they rode in.

Walter swung from his pony, and, hurrying to the tents, glanced into each in turn.

"That's queer. Looks as if no one had been here in a month. Well, suppose we unpack and wait."

"Somebody has been through these tents in a hurry," declared Tad after having made a hasty examination on his own account. "Did you notice that everything in the Professor's tent had been fairly turned inside out? There are our bows and arrows lying out there near where the camp fire was."

Now, the boys began to feel real concern.

"Tether the ponies and we will go out and see if we can find them,"

commanded Tad Butler.

"Shall we take our guns?" asked Stacy.

"Better not. Take your bows and arrows if you wish. We are going on the trail of two-footed game now, and we do not want to have guns. We might use them and be sorry for it afterwards."

Realizing the wisdom of his words, the boys laid aside their rifles, grabbed up their bows and quivers, and following Tad, who immediately struck off in the direction of the cave. Tad's own experience there was still fresh in memory.

At the entrance, they halted.

"Look at that! What do you think of that?" exclaimed Tad.

Above the entrance to the cave hung suspended a broad strip of sheeting. On it had been scrawled, evidently with a piece of blunt lead, the words:

THIS CLAIM BELONGS TO AB DURKIN. KEEP OFF!

The boys gazed at each other in amazement.