THE creature that was slowly moving toward Joe was as large as his hand, with long, powerful legs that were doubled ready to spring. And Joe well knew what that spring would mean.

The youth viewed the hideous scorpion with a terrible awe, fearing to move lest it become angered and charge. What was he to do? He knew he could not get up in time, for his terrible enemy would be upon him. Yet if he should remain sitting, he would surely feel the hairy mass upon him in a very few seconds.

Slowly Joe reached into his holster for his pistol. He was a poor shot with such a weapon, but the chance had to be taken. Still there was a possibility that he might kill the huge spider by throwing the gun at it.

With a sudden movement the youth drew out the automatic and carefully but hurriedly threw it with all his strength.

Then his heart sank as he saw the gun whiz past the scorpion and roll across the hard ground. The sudden movement angered the creature still more, and it crouched as if to charge.

Suddenly, as a last resort, Joe sprang to his feet and dodged to one side, just as the scorpion left the ground. As the result the charge was unsuccessful, the huge spider alighting several feet to the youth’s left.

The next moment Joe was in the tent, looking about nervously. He picked up his rifle and dashed back outside.

The scorpion was slowly crawling toward the entrance to the tent when Joe took careful aim and fired.

His aim was true. The small bullet caught the creature squarely, shattering it into pulp, which flew in several directions.

After watching the remains of the scorpion for a moment, Joe turned about, to find Dr. Kirshner and Bob standing beside him with small rifles.

“That was a wonderful shot, Joe,” praised the archÆologist. “Bob and I happened to have our rifles and would have taken a shot at the scorpion if you had missed.”

“So you saw, did you? Well, I don’t mind saying that I was frightened stiff for a few minutes. Thought sure I was a goner.”

He was forced to tell of the entire experience, and in the end his listeners looked grave.

“A very narrow escape,” said Dr. Kirshner, who, along with the naturalists and Fekmah, had listened breathlessly.

“Scorpions are terrible adversaries,” said Mr. Holton soberly. “The fluid they inject is extremely poisonous! From now on we’ll have to watch more closely.”

After breakfast the explorers continued on the dromedaries. They were to reach another stretch of sand dunes late that afternoon, Tishmak told them.

“Sand hills will seem good after these endless miles in the Tudemait Plateau,” remarked Joe. “But there won’t be any shade, and there is a little here from the rocks.”

“Wait till we get to the Ahaggars, if you want shade,” smiled Mr. Lewis. “Some of that region resembles the mountainous part of Arizona. There are deep ravines, narrow valleys, high peaks, unknown caves, and many other remarkable phenomena of nature.”

“That is where our journey comes to an end, isn’t it?” asked Bob.

“Yes. In the southern part of the Ahaggar range. Thus far, Fekmah hasn’t had much need of the map, because he has directed us more by compass. But when we see the mountains, it will be necessary for him to consult it frequently. Whether or not it will prove accurate, made from memory as it was, we have yet to see.”

The way now led through a dry river valley, which wound through the many black rocks. Some of the rugged hills near by towered to two and three thousand feet, their perpendicular sides gray or deep black.

There was sparse vegetation, but a few gum trees were scattered about over the hard soil.

Tishmak had informed them that they would come to a well some time that afternoon. The water, he said, would be very cool, for it came from far underground.

“I’d like to see that Land of Thirst you were talking about,” remarked Joe to Fekmah, as the Arab mentioned the well of cool water that lay ahead of them. “It must be an interesting region.”

Fekmah shook his head.

“Caravans avoid it much as can,” he said grimly. “Too much danger of falling dead. Then, too, it is supposed to be inhabited by evil spirits.”

“Evil spirits?”

“Yes. Superstitious natives near there never see parts of it. I much glad we not have to go through it, because we sure to get very much thirsty.”

Shortly after the explorers had passed around a large hill they heard camel steps from behind a sharp corner in the river bed.

“Quick!” directed Dr. Kirshner. “Let’s hide in back of these rocks. It may be more bandits.”

The adventurers drove their dromedaries out of sight and then followed, looking about cautiously.

The sound of footsteps grew louder, and soon a small caravan of natives came into view, looking very strange indeed with their faces tightly covered with black veils.

“Tuaregs!” exclaimed Dr. Kirshner, who had made a study of the peoples in the Sahara. “Tuaregs at last!”

He rode out from behind the place of hiding and shouted a friendly greeting in their own language. The people at once called back and moved on up to the archÆologist.

“Guess we might as well go out,” smiled Mr. Holton, urging his camel to move forward.

Soon the others joined Dr. Kirshner, who seemed to be having no trouble in understanding the people.

“They live in the Ahaggars,” explained the archÆologist, after a few minutes of conversing with them. “They’re on their way north to In Salah. That’s a town of considerable importance.”

The natives did not stop long, and the American expedition was also anxious to be going.

“I didn’t know Tuaregs were found this far north,” said Mr. Lewis, as the people disappeared from view. “Their home is in the lower Ahaggars, and they seldom ever, if what I’ve heard is true, wander far away.”

The explorers stopped before noon for the meal and rest. Then, at two o’clock, they continued on their way, anxious to leave the plateau behind.

Suddenly, as they gradually ascended a long grade, an agile form darted out to one side of Bob’s dromedary, its red coat showing brightly in the sunlight.

“A fox!” Bob exclaimed and raised his rifle to his shoulder.

Glancing along the sights, he pulled the trigger. There was a howl of pain as the bullet struck the animal broadside. Another howl; then silence.

“You got him!” cried Joe, delighted.

“A big specimen, too,” declared Mr. Lewis, getting out his knife.

The animal was carefully but rapidly skinned and the hide placed in the solution of preservative.

“Already we have a large number of specimens,” said Mr. Holton, as they left the skinned body behind. “And we hope to see a good many other animals and birds as we pass on.”

Late that afternoon the adventurers came to the well that Tishmak had told about, and found the water very cool. It reached the surface in a shady spot among the many high rocks.

All drank with a thirst that came from long traveling in a dry, hot region. Bob and Joe especially welcomed it, the latter declaring it better than flavored beverages.

“That’s right,” agreed Mr. Holton. “One can drink many things, but water is, after all, the old stand-by.”

When the containers were filled, the explorers rested in the shade of the rocks. There was something about that spot that made them hesitate to leave it behind. Perhaps it was the cool water, or it might have been the wall-like formations of stone all about.

Finally Tishmak got up and mounted his dromedary, motioning for the others to follow suit.

All the remainder of that afternoon they trudged on over the Tudemait Plateau. Slightly to their surprise, they had not yet reached the region of sand that lay at the south of the plateau. Fekmah especially was very restless, saying that he could not understand why the rocky region had not been left behind shortly after the midday rest.

“It supposed to be only about a hundred and seventy kilometers [about one hundred miles] across, and we have traveled at least that far,” he said, very much perplexed.

“Perhaps we have followed the arc of a circle,” suggested Mr. Lewis. “Suppose you ask Tishmak.”

The guide was also in the dark, not being able to give an explanation.

“Well,” said Bob, “it might be well to keep going awhile longer. We’ll surely come to the sandy region before long.”

The others thought this good advice, but late that evening they were still on the plateau.

They retired that night with high hopes that the morning would bring good fortune. During the last few hours they had had an uneasy feeling that their efforts to find the region of sand were in vain.

The next day they were off early, after a hurried breakfast.

“We’ll get out of these rocks some time this morning,” predicted Mr. Lewis with a smile.

And he was right. Gradually the boulders they passed grew smaller and the soil more loose. By the time they had stopped for the noon meal they were again among sand dunes.

The heat was now terrific. If it had been warm before, it was scorching now. Everywhere they went they were under the blaze of the fierce sun. How the camels managed to keep from burning their feet was a mystery to the youths.

Their throats were parched, their tongues numb. Water, water! If they could only drink and drink and drink! But only small amounts were allowed to be taken, for this region was many, many miles across, and there was no well or oasis anywhere near their path of traveling.

“If we have much more of this I’m afraid I’ll fall off my camel,” said Bob with a grim smile.

“Not quite that bad off, are you?” laughed Dr. Kirshner. “Dying of thirst is a rare occurrence in this part of the Sahara. But it does happen sometimes, and it is a tragic death indeed.”

“Worst thing is,” explained Mr. Holton, “there is a time when the victim of thirst would die should he touch water. In that case, water is virtually a poison.”

The sand hills that they were passing over were much lower than those in the country below Wargla. The desert stretched away to the horizon in endless waves, which, as far as the travelers could see, were unbroken.

Vegetation was scarce, only a scattering of yellow plants dotting the dunes. This promised to be a disadvantage to the dromedaries, for previously they had occasionally nibbled on the trees and shrubs that were clustered about.

“Look at the sky,” said Joe, turning his gaze upward.

“Funny color, isn’t it?” Bob returned. Then, as he peered into the distance, he uttered an exclamation of surprise and fear.

But the others had seen also and were equally as excited.

Away to their right a heavy mist had risen and was rapidly turning reddish.

“A sandstorm!” cried Fekmah in great anxiety. “A sandstorm is coming!”