DOWN a little valley between two high mountains rode four explorers, their eager eyes penetrating every crevice and notch in the mountainous country about them. High-power binoculars were turned upon every level stretch, rifles were fired at regular intervals, voices were brought to new swells. It was a search that under ordinary circumstances would have brought Dr. Kirshner and Joe back in a very short time.

Finally, after the searchers had been out several hours and darkness was beginning to fall, Mr. Lewis stopped and buried his face in his hands. He realized that defeat was staring them in the face.

“Guess they’re really lost,” sighed Bob Holton, his face extremely sober.

“Or else something has happened to them,” added Fekmah in a voice that he tried to keep steady.

Mr. Lewis said nothing, but he feared all too much that the Arab was right. And yet, he reasoned, they were likely to be very careful and not take chances. Still that would not prevent nature or wild tribes from harming them.

Mr. Holton, however, was very optimistic. He believed that, despite the length of their stay, the two were safe. Perhaps they had fallen asleep from exhaustion or had wandered farther away than they had intended and were forced to spend the night in the mountains.

Tishmak had been left at the camp, as it was thought best to have someone there in case the archÆologist and Joe should return while the searchers were gone.

“We’re a long distance from camp,” said Mr. Lewis, as the searchers sat on their camels at the brink of a deep gully. “Shall we try to get back tonight?”

“I’m in favor of it,” returned Mr. Holton impatiently. “Of course we left word with Tishmak that we might spend the night away, but he may be greatly worried. Then, too, he might not be safe there alone.”

The others thought this good advice, and turned the dromedaries back up the lane. They could possibly get half of the way there before the darkness would halt them. Then the moon would probably furnish sufficient light to continue.

“Here’s hoping they will be at camp when we get there,” said Bob.

But Tishmak was the only one who greeted them when finally they rode wearily up to the tent.

The guide had fully expected to see the lost ones return with the others, and his face wore an anxious look when he saw that their search had been in vain.

Fekmah immediately related their past experiences, concluding by asking what Tishmak thought had happened to them.

The guide replied that, as Mr. Holton had said, perhaps they had wandered farther away than they had intended and were forced to spend the night away. Of course, he went on, tragedy might have come upon them, but he doubted this very much. The Tuaregs who inhabited this region were friendly to strangers, showing excellent hospitality. And both Dr. Kirshner and Joe he considered able to take care of themselves. He finished by saying that, through his guiding numerous expeditions into the Sahara, he believed himself capable of judging a true explorer.

When Fekmah translated this to the Americans, they were much relieved. Especially was Mr. Lewis hopeful. He had confidence in Joe and believed him equal to taking care of many tight situations.

Notwithstanding this, there was little sleep for any of them that night. When at last the sun began to peep through the distant mountains they were up ready for action.

“We’ve got to find them today,” said Bob, gritting his teeth.

“We will, if they are anywhere around here,” Mr. Lewis added. “Let’s hurry and have breakfast.”

As soon as the meal was over, they again started out on the search, this time taking Tishmak and leaving Fekmah. The latter thought this the best procedure, as the guide could render more assistance in searching the mountains.

Taking the opposite direction from the one they followed the day before, the explorers rode off, bidding warm farewells to Fekmah.

For several miles they rode over the smooth surface of a dry river bed. Then they turned and followed a path around a small mountain.

“Wonder how this path got here?” said Joe, as they plodded up the hill.

“Wasn’t made by nature,” concluded Mr. Holton, observing the regularity that was persistent with every step.

He resolved to use his limited knowledge of the native language and inquired of Tishmak, for surely the guide would know.

When finally the latter understood, he replied that the lane had been made by Tuaregs who inhabited this region. Perhaps the path would lead them to a village.

But the searchers trudged on around the hill without seeing any signs of natives. However, they finally broke away from the narrow way and emerged on level country.

They were now on a high plateau, with towering peaks on all sides of them. As far as the explorers could see, there were no breaks or ravines anywhere about.

Rifles were discharged at intervals, and hoarse shouts often rent the air. At every few steps the searchers stopped to look about, almost expecting eventually to find the lost ones nearer than they thought.

Once Bob thought he heard footsteps, but several minutes of listening convinced them that no one was about. Perhaps it had been his imagination.

“Sounded like someone was coming toward us,” the youth said. “But I guess I just thought so.”

“We’ll have to keep our ears and eyes wide open,” Mr. Lewis reminded them. “If Joe and Dr. Kirshner are anywhere around here, it might be possible to hear them.”

“Isn’t likely that they fell into the hands of Tuareg raiders, is it?” asked Mr. Holton.

“Tishmak said not,” Joe’s father returned. “He thinks that the Tuaregs around here are friendly and peaceful.”

A little farther on they passed several large slabs of rock that were covered with ancient inscriptions and drawings. Dr. Kirshner would surely throw a fit of delight if he could see them. But, thought Bob, perhaps he had already come to them and was searching for more, quite forgetful of the necessity to get back to camp. But no, this could not be, for Joe would realize that necessity if the scientist did not.

At noon they stopped for lunch under a large crag that resembled an inverted hook. There was plenty of water in their containers, giving each the opportunity to satisfy his thirst.

There was not much conversation during that rest, for they were all busy with their thoughts. And those thoughts were anything but cheerful. But they refused to give up hope so soon, for another half-hour might see the two lost ones back with their friends.

Scarcely ten minutes were spent in the shade of the rock. Even then Mr. Lewis felt that that time had been wasted.

“Something might have happened to them during that time,” he said, greatly worried.

Mr. Holton laid a hand on his friend’s shoulder.

“Snap out of it, Ben, old man,” he begged. “I’m willing to bet that they are safe and well. And I firmly believe we will find them before another day will pass.”

Mr. Lewis did resolve to cheer up and be hopeful; but still he possessed a haunting fear that perhaps tragedy had come upon them.

The sun blazed very hot that afternoon, scorching the already baked soil. This did not hinder the progress of the searchers, however, who trudged constantly on.

Suddenly, as they passed over a wide valley strewn with rocks and dotted with cracks and ravines, Bob stopped and looked about expectantly. The others had also caught a sound.

The next moment the explorers were seized with fear, for ten or twelve evil-looking Arabs darted out on dromedaries and rushed toward the explorers.

“What’s this!” cried Mr. Holton, as one of the men caught hold of his camel.

There was no chance to use their guns. The Arabs were on the lookout for any treachery.

Suddenly Bob saw a chance and, drawing the reins of his dromedary, he dashed away at full speed for a short canyon between the rocks.