Frank and Joe examined it curiously. “What is it?” Frank asked.
Cap spoke triumphantly. “Unless I'm very much mistaken, it's a bone from the leg of an ancient horse. It was turned up by the boulder when it ripped down the hill.”
“An ancient horse? You mean that there were prehistoric horses in this country?” Joe asked.
“I thought the horse was a comparatively recent animal,” Frank chimed in.
“Oh, no, the horse has been part of the earth as far back as man can tell. As a matter of fact, the evolution of the horse is one of the interesting mysteries of paleontology.”
“What do you meanâmystery?”
“No one has figured out why the horseâa much smaller one than the present kindâlived here from prehistoric time until the Pleistocene period, then became extinct. The horse as we know it today was imported.”
“If this fossil is from one of the earlier breed,” Frank observed, “it must be mighty valuable.”
Bailey nodded. “If I'm right, it could mean there may be many valuable fossils here besides the prehistoric camel my uncle discovered.”
Cap was so excited that all thoughts of his brush with death were forgotten. When the boys told him of the two riders they had seen in the distance, he merely nodded.
“If they did tip the boulder, actually they did us a favor. Look at the digging they saved us.”
“But if they continue to make attempts on our lives,” Frank said, “we'll have to be on guard every second.”
“Is there any possibility of getting help in this excavation job?” asked Joe.
Cap shook his head impatiently. Elated by the discovery of the fossil, he was ready to start work immediately.
“If those men were trying to stop us by toppling the boulder, they probably think we're dead, and won't be coming back,” he added.
Frank and Joe, eager themselves to see what other fossils might be turned up, fell to work in earnest.
For several hours they sweated as they dug deeper into the sand and hardpan.
“I've hit something!” Frank suddenly called out. When it was uncovered, Cap Bailey was enthusiastic.
“Boys, I'd bet my last shirt that this bone was once part of the shoulder structure of the ancient camel Uncle Alex thought he'd found!”
“Looks like an oversize ham bone that some prehistoric dog buried here,” Joe said wryly. He sat down in the sand and propped his weary head on one grimy fist. “You really have to be interested in fossils to work this hard,” he groaned. “I'll never think of geologists and scientists again as old fuddy-duddies.”
Cap and Frank burst into laughter.
“Better buck up, Joe, we've barely started.” Cap clapped him on the back and asked him to carry the ancient bones up to their permanent camp, and to put the fossils under a protective tarpaulin.
“What are we bothering to cover these things for?” Joe queried. “Nobody's been taking very good care of them for a couple of million years.”
“Except nature,” Cap said. “She's been protecting them from the weather all this time.”
Joe nodded and set off across the slippery sand and through the defile.
Cap and Frank picked up their shovels and resumed work, chopping out large chunks of near-petrified sand. The pit grew deeper and deeper. They were working in silence, intent upon the task at hand, when Frank began to feel uneasy.
Where was Joe? He had been gone much too long for a mere trip to camp. Frank climbed out of the excavation and scanned the slope. He could not see his brother.
Worried, Frank hurried toward the plateau. Had something happened to Joe?
Sensing trouble, Cap followed Frank, reaching the camp a few minutes later.
“Joe doesn't answer,” Frank said. “But,” he added, pointing to a tarpaulin wrap, “there are the fossils. He's been here.”
“How about the horses?” Cap asked, and quickly investigated the tiny meadow where they had tethered the animals. All three horses and the pack mule were grazing contentedly.
“I'll try our distress signal.” Frank gave a long, piercing birdlike whistle. It was the secret whistle he and Joe used when in trouble.
But no answer came, and again Frank gave the shrill, high-pitched call. Listening intently after it ended, all he and Cap could hear was the breeze as it gently moved a few leaves high above them.
“But what could have happened to Joe?” Cap asked. “If he met with any sort of trouble, we should have heard some kind of sound.”
After discussing the situation, they decided on a systematic search of every foot of ground between the camp and the slope. They had got as far as the ledge when Cap held up a warning hand.
“Do you hear something?”
For a moment there was only silence. Then, almost as if from under their feet, in the depths of the earth, they heard:
“Frank! Fra-a-a-a-nk!”
The voice was so low and indistinct that Frank thought he might have imagined it. But a look at Cap's excited face convinced him that his companion had heard the call too.
Where was it coming from?
After several minutes of frenzied search they had the answer. A flash of light from between two huge rocks just below them at the very edge of the slope caught Frank's eye.
“Down there!” he cried excitedly.
He and Cap peered into the crevice. This time a light shone squarely in their eyes, and they realized that they were staring into the beam of a flashlight.
“Hey! Come on down!” It was Joe's muffled voice. “It's a cave, and somebody's here!”
Examining the opening, Frank and Cap realized that a man could easily squeeze through it. Rigging a stout rope around a large boulder as a means of ensuring their exit, they wriggled down the rope and into the passageway. In a minute Frank stood beside Joe on the floor of a sizable cavern.
“You're okay? You didn't have an accident?” Frank asked.
“Not exactly,” Joe answered. “I tripped, fell off the ledge, and rolled down here. When I saw this cave, I thought I'd investigateâand look!”
He pointed with his flashlight to one of the recesses of the cave. Propped against the sloping wall was a skeleton!
“Nice cave mates you pick for yourself, Joe!” Frank said jokingly. He spoke lightly, but a shiver ran down his back as he gazed at the skull.
“Listen, fellows, that man probably died from suffocation or starvation in here,” Cap said. “I wonder whether he had been living in the cave.”
“Anyway, he had plenty of equipment with him,” Joe said. “See?” His flashlight picked out a pile of long, rusty iron pipes near the skeleton.
“Say, they're the same kind as the pipe you found on the slope, Joe!” Frank cried. “This old geezer must have brought them down here for a purpose.”
“He probably was a prospector,” Cap decided. “I wonder what he planned to doâdrain the swamp?”
“But what for?” Joe asked.
“Maybe he had panned some of the slope,” Frank said, “and believed it might be a good prospect for placer mining.”
All three joined in rummaging around the cave with their flashlights. Cap was about to suggest that they return to the surface, when Frank excitedly cried out:
“Come here, quick!”
Hurrying over, they found him in a dark corner. He had spotted a gleaming new pistol.
“Someone else has been here, and not long ago,” he announced. “There's not a speck of rust on this gun.”
Carefully Frank wrapped a handkerchief around the weapon and picked it up. By the beam of his tiashfight, they all could clearly see the smudges of someone's hand along the barrel.
“I have that fingerprint powder in my pocket, I think,” Joe said. “Let's see what those prints look like.”
He dusted the smudges, and Frank examined the clear prints. There was a familiar swirl on one that looked like a thumbprint.
“Doesn't that remind you of the thumbprint of a certain character named Willie the Penman?” Frank asked excitedly.
“It sure doesâon the kitchen window of Cap's house,” Joe replied.
“If so, what's our next move?” Cap asked.
“To prove our point,” Frank replied.
He proposed that they leave the pistol in the cave, on the chance that the owner would return, and they could capture him then.
“We can watch from above,” the young sleuth suggested.
“Good idea,” Joe said, and Cap agreed. Making sure they had left no telltale traces of their presence, they climbed up the rope through the cleft in the rocks to the ledge above.
All agreed that further digging for fossils must wait upon this new development. There was a good chance that the owner of the pistol had been watching them.
Evening chores were split up among them. Cap hid the precious relics, while Frank prepared supper, and Joe watched the cave entrance from a spot in the shadows. The trio ate supper in Joe's hideout.
“We'd better stay right here tonight,” Cap proposed.
By dusk the three watchers were ensconced in a makeshift shelter. Lying prone, they could see every bit of the slope around the entrance to the cavern. A full moon provided all the illumination needed.
“We'd better agree on shifts,” Cap suggested, and it was decided that Frank would have the first watch. Joe would take over at midnight, and Cap at three in the morning.
There were no disturbances during the night and at six o'clock Cap awoke both his companions.
“I was sure somebody'd come back for that pistol,” Joe said, disappointment in his voice. “Well, I'm going down to have another look in the cave.”
“I'll go with you.” Frank crossed the slope with his brother and descended to the floor of the cave. A moment later the boys looked at each other in astonishment.
“The pistol's gone!” they cried simultaneously.
“But how could anyone have taken it?” Joe demanded. “Not a soul came near the cave.”
“Unless,” Frank said, “there is another entrance.”
It took only five minutes for the boys to investigate Frank's theory. After probing every niche and cranny of the walls, he found a loose boulder which looked as if it had been set in one corner for a purpose. Moving it a bit, Frank saw daylight.
“Come on,” Frank motioned, and the boys crawled through.
They found themselves farther along the slope, around the corner from the spot where they had lain watching all night!
“What a couple of duds we turned out to be,” Frank said in disgust. “And what a laugh Willie or whoever it was had on us!”
“I wonder if he saw us lying there in wait,” Joe pondered.
Replacing the stone that covered the entrance, they called to Cap and showed him the second underground entrance. The teacher's reaction was almost identical with Frank's, and he added, “This place may be riddled with secret caves, and eventually bullets, if we don't watch out.”
A short conference produced one decisionâto radio Fenton Hardy and tell him that Willie the Penman might be in the neighborhood of Wildcat Swamp.
Frank unpacked the powerful sending-and-receiving equipment. They surveyed the terrain for a good working spot.
“Below this mountain ridge, we'll certainly have trouble getting a good signal,” he murmured, and decided that the only possible way to make contact would be to use the self-inflatable balloon they had brought to carry the antenna aloft.
Soon the little gas-filled bag was high in the sky, trailing its aerial wires. Frank tuned in the secret frequency that the Hardys used for family communication. He was about to give it up as hopeless when suddenly a voice said:
“Fenton Hardy speaking. Come in! Come in!”
Quickly Frank reported that they were well, and then told his father of the latest developments.
“Will you get prints of Flint, Turk, and Willie from Warden Duckworth and send them to Red Butte as soon as possible,” he requested. “We'll check them with the ones on the pistol we found last night.”
His father agreed.
“How about the train robbers?” Frank asked. “Any news?”
“I have a hot lead I'd like you boys toâ”
Mr. Hardy's voice faded completely. There was not a sound from the receiver.
Startled, Frank glanced toward the airborne antenna, just in time to see the balloon, deflated, plummet to the earth.
Now there was no chance to find out what the detective had intended to say!
CHAPTER VIII
Ordered Out
“WHAT happened?”
Cap's cry was hardly out of his mouth when Joe and Frank were racing off to retrieve the deflated bag. It dropped out of sight, but by following the dual cord which had secured it to the set and carried the antenna line, they soon located it. The balloon hung limply from the branches of a tall pine. Frank shinned up, unfastened the bag, and brought it below for examination.
“Punctured,” he said. “Look at those holes.”
Cap came running up just in time to hear Frank's remark.
“But howâso high up in the air? Nobody could throw a stone that farânot even a baseball pitcher!”
Frank's face was grave. “I believe someone fired a bullet through it.”
“But I didn't hear any shot,” Joe objected. “Did either of you?”
“The shot could have been fired from the other side of the ridge,” Frank commented.
Cap nodded. “Especially if the wind were blowing the other wayâwhich it isâwe wouldn't have heard the shot.”
“I wonder,” Frank mused, “whether some cowboy took a potshot at it just for fun, or if our friend Willie did it deliberately.”