“WHAT!” cried Bob excitedly. “Stop for the day! We—we can’t. Our time is worth too much!”

The naturalist laughed unwillingly.

“This time it’s a question of what we have to do,” he said dryly. “If the blackness increases, it will be suicide to plunge through it with so many rocks and walls of stone near.”

The boys and Mr. Holton rode on up to the front of the caravan, where Tishmak and Fekmah were visibly moved with fear.

The darkness was becoming more intense with every minute. Soon the explorers could not see one another.

“It might be well to get off our dromedaries,” suggested Mr. Lewis. “If this is to continue long, it won’t pay to remain mounted.”

“This is likely to mean a loss of several hours,” said Fekmah gravely. “Then again, the fog of dust might pass away in but few minutes.”

“Worst thing about it is the difficulty to breathe,” pointed out Dr. Kirshner. “Tragedy has been known to come upon caravans in this manner.”

It was indeed stifling, but the adventurers managed to get air through the dust. They feared every minute that time would bring about an impossibility to breathe.

Much to their relief, that dread moment did not come, and after a half-hour the blackness gradually thinned out until it again became light.

“Thank goodness!” breathed Mr. Lewis. “Now let’s get on our way again.”

Still more the country was changing. The rocks became more jagged, taking on many shapes and forms. Small trees and plants became more abundant, causing the region to resemble certain areas of the American desert. And along with this plant life came numerous traces of wild animals.

“Wish we would run across a fox,” said Joe. “I’m anxious to shoot anything.”

“Probably will,” returned Bob. “I guess there are not only foxes but jackals and other small game. There should be much more here than in the sandy section.”

The party stopped at eleven o’clock for the meal and midday rest. This time the dromedaries alone were to be the guards, for they had already proved their efficiency in detecting unusual noises.

At two they were again on their way, climbing a gentle slope widespread with sharp rocks.

“Seems strange to get away from the sand dunes,” remarked Bob. “It hardly is like a desert now.”

As they passed up a rocky hill, Fekmah called a halt.

“We have come to the Tudemait Plateau,” he announced, getting out the map that he had made from memory. “That sharp peak in the distance is one of the landmarks. Now we pass through this plateau for rest of today and part of tomorrow; then come to another sandy stretch.”

“Then what?” inquired Mr. Holton.

“Get to Ahaggar Mountains,” the Arab replied. “We have to follow compass more close from now on, because must see peak called Illiman. Then we know we near treasure.”

“And here’s hoping those two thieves haven’t gotten there first and taken everything away,” said Joe.

That afternoon they came to a small well and refilled their containers, which were beginning to get low. Despite the fact that the water was exceedingly warm, it was greatly welcomed by the explorers.

A high hill was before them, and Bob suggested that they climb to the top afoot and make out the character of the land ahead of them.

The others were in favor of doing so, for Fekmah might catch sight of something that would be recognized as a landmark on the map.

The climb was tiresome but easy, the many boulders offering footholds. Finally they reached the top and turned their gaze toward the horizon.

“What’s that ’way over there?” asked Joe, pointing to a narrow valley walled closely by high rocks.

Mr. Lewis and Mr. Holton had their binoculars strapped over their shoulders. They took them out and peered into the distance.

Suddenly Mr. Holton started.

“It’s a village!” he exclaimed, and Mr. Lewis nodded. “A village of Arabs. Look at the low huts of sun-baked mud,” handing the binoculars to Fekmah.

“Yes,” said Fekmah, gazing out through the glasses. “Suppose we go over there and see them. They treat us all right. It not take much of our time.”

“All right,” returned Dr. Kirshner. “I’m anxious to make a casual study of them. They might have some primitive implements that belonged to their remote ancestors.”

The adventurers made their way down the hill and mounted their camels. Then they rode off toward the distant valley. It was a good distance away, and perhaps hard of access, but the explorers were determined to find it.

In less time than they had expected, they came to a spot that would probably afford an opening into the valley. For a few minutes they wound in and out among the rocks. Then they came within sight of the village.

A crowd of Arabs ran out to meet them, uttering hearty greetings. It was evident that expeditions rarely passed within sight of their dwellings, for they were very excited.

Tishmak and Fekmah conversed with the people in a very friendly manner and then introduced the others of the American expedition.

Dr. Kirshner and the naturalists found it almost impossible to understand the language, and they were satisfied with Fekmah’s translations.

“A good chance to take some movies,” said Bob, getting out the camera.

“Don’t suppose the Arabs would object,” added Joe. “At any rate, we’ll risk it.”

The youths cranked off several scenes of the Arabs and their village. It was clear to the explorers that the people had never seen a motion-picture camera before. The strange purring box was an object of curiosity, and they crowded around like so many children.

To the Americans, these people were of great interest. The men and women dressed almost alike, in a long, white robe that reached to the ankles. A tight-fitting cloth was wound around the head, and the back of the neck was protected from the sun by a black veil. They were of a naturally swarthy complexion, which was still further darkened by the fierce desert heat.

“Not very pleasant to look at,” said Bob to his chum. “But they sure are giving us a hearty welcome.”

“That’s probably because they’re so unused to seeing strangers,” Joe remarked. “Nearly all friendly natives are that way.”

The Arabs led the explorers into the main part of the village, where there was a large open space before the chief’s, or sheik’s, hut. Suddenly the head native stopped and pointed to a distant large rock. He babbled animatedly to Tishmak and Fekmah, whose faces took on a look of disgust.

“Sheik say over there is a place where they bury those guilty of witchcraft,” Fekmah explained to the Americans. “They put to a terrible death, and then their bones taken over there.”

Mr. Holton shook his head repulsively.

“Ignorance is the root of evil,” he said. “These people are even worse off than the Negroes of the Congo. They so infrequently come into contact with civilization that they have degenerated into a state of almost nothingness.”

“With even more respect for Fekmah and Tishmak, the Arabs in many remote sections of the Sahara are a bloodthirsty, treacherous, and immoral people,” put in Dr. Kirshner. “They do not at all compare with their brothers in Algiers and other places nearer the coast.”

Fekmah nodded.

“Praise be to Allah that I was not born here,” he muttered.

The sheik invited the explorers to stay for dinner, but Fekmah politely refused, saying that they must hurry on.

“We have many miles to go yet,” he told them in the native tongue. “If we are to get far today we must be going now.”

The explorers left the village for their camels, the Arabs shouting warm farewells.

“Professor Bigelow ought to be here,” smiled Joe, referring to a famous anthropologist who had accompanied them on their expedition in Brazil.

“Wouldn’t he be tickled,” laughed Mr. Lewis. “But then—maybe he’s already been here. He has been about everywhere else studying primitive people.”

Soon the adventurers were out of the narrow valley, again taking up the journey. They were glad to get started again, welcoming any new sight in the way of oddly shaped rocks, deep valleys, and other formations of nature.

Darkness was rapidly falling, but they kept traveling until it became impossible to see ahead. Then Tishmak held up his hand for them to stop.

Again they waited for the moon, not continuing the trip until it came out.

“Tonight we must make up for the lost time at village,” said Fekmah. “We can stand to stay up an hour later.”

It was not until eleven o’clock that they finally came to a stop in a wild, rocky region. The tents were put up for the night.

The next morning the explorers were barely up when Joe happened to notice something crawling toward him as he sat near the tent.

He was up in a moment, looking about fearfully.

“A scorpion!” he cried excitedly.