BEFORE long the little town of Wargla vanished from the horizon, and a sense of dread crept over Bob and Joe at the thought that they were now shut off completely from the outside world. What tragedies might befall them before they would again see the United States? There were all sorts of dangers out on that vast stretch of wasteland. Would their lives be threatened—and possibly lost?

Bob glanced back and saw the worried look on his chum’s face. That Joe’s thoughts had been the same as his was evident.

“Snap out of it, Joe, old man!” he said, rousing himself. “Think of the fun we’ll have. And the strange sights we’ll see. It’ll be great. And behind it all lies adventure.”

Joe nodded. His face took on a smile as he anticipated the coming events.

“Wonder what adventures we’ll have?” he mused. “But I suppose we’ll soon see.”

The boys were at the end of the little caravan, keeping an eye on the pack camels. Although ropes had been fastened from the back of one animal to the head of another, keeping them in single file, it was best to guard them closely, for anything might happen on the desert.

Tishmak, acting as the guide, was in the lead, followed by Dr. Kirshner and the youths’ fathers. Fekmah was in the middle of the line. The twenty dromedaries were spread out over perhaps a quarter of a mile and trotted at a speed that promised to cover many miles in a short time.

“I guess dromedaries don’t compare with camels when it comes to fast traveling,” remarked Joe, recalling something that Fekmah had said some time before. “The one-hump animal makes four times as much speed.”

In the early morning, as it was, the atmosphere was chilly. Bob and Joe welcomed the warmth of their tight-fitting coats.

“I never thought I’d need a wrap on the desert,” smiled Bob, fastening the collar around his neck.

“We’ll need more than coats at night, if what Dr. Kirshner said is true,” said Joe. “Gets cold as Greenland’s icy mountains.”

“Seems strange, doesn’t it?”

“Yes. But you remember it was the same way in Brazil. And that’s about as hot a country as there is anywhere.”

Soon the flat hill of Gara Krima, dominating the sandy plain, could be seen, its smooth surface tinted with many colors. Then it was left behind, and the explorers came to a region of loose sand. The dromedaries found it more difficult to plod through, and slackened their rapid pace somewhat. Although their feet were specially adapted for traveling on sand, they made much better time on hard surfaces.

“Look at the dust they’re making,” observed Bob, as a dense cloud of fine sand particles arose, making it necessary for the youths to ride a short distance to one side of the pack animals.

“They don’t believe in kicking it up, do they?” Joe said dryly.

After a while the sun came out in full splendor, sending its dazzling rays down on the scorched sand. Bob and Joe soon perspired freely, and were glad to remove their coats.

“Whew!” gasped Joe. “I’d give anything for a drink of water.”

“So would I,” his friend replied. “I’m going to ride on up and ask for one.”

“Remember me while you’re there.”

It was a good distance to the other end of the caravan, but the sure-footed dromedary trotted along briskly. Fekmah waved as Bob passed.

“How about a drink of water, Dad?” asked Bob, coming up to his father’s camel.

“Go to it,” was the answer. “We’ll come to a well before long, and refill the canteens.”

The third and fourth animals back were the water carriers, and Bob lost no time in filling his container. Then he drank freely of the refreshing liquid, and felt new life creep into him. Although warm, the water did wonders in quenching his thirst.

Again he filled the container and rode back to his friend, who was delighted.

“I was afraid they wouldn’t let you have it,” Joe said, wiping the perspiration from his brow.

“Wouldn’t have, only there’s a well not far away, and we’ll have a chance to refill the tanks.”

“Well, huh? Wonder if they’re this close together all along?”

“Let’s hope so.”

A little later the explorers passed a scattering of bones and skeletons that were partly covered with sand. They were dry from age, having probably been uncovered by a sandstorm.

“Camels’ bones, I suppose,” remarked Joe. “They’ve become overcome with thirst, most likely.”

“Who knows but that the skeletons of their riders are there some place, too,” said Bob, his face sober.

The sight was not a pleasant one, for it brought to mind the fact that it was altogether too possible that their little caravan might perish for want of water also. Some time elapsed before the boys resumed their cheerful mood.

As they traveled on, the ground became strewn with small red pebbles that shone brightly in the dazzling sunlight.

“I guess most of the rocks here are red,” remarked Bob, who had studied books on the Sahara.

“Burned that color by the sun, huh?”

“Seems reasonable, doesn’t it? Come to think of it, though, the ground in the Land of Thirst is black.”

“The Land of Thirst?”

“Yes. I heard Fekmah talking about it this morning. It’s a region where there are few or no wells, and you have to be very careful to have a good supply of water in the tanks before you plunge into it.”

“Looks like even then it would be dangerous. What if a storm or something would hold you back for a long time?”

“Have to take that chance,” Bob replied. “Wouldn’t doubt that quite a few caravans come to a tragic end there.”

“Will we go through it?” Joe asked.

“Fekmah said we might,” was the response.

Finally they came to the well that Mr. Holton had told about. There was a steady flow of water, which was comparatively cool.

“Drink all you want,” said Dr. Kirshner. “Tishmak says we won’t see another for a long time.”

The explorers drank and drank, until they could hold no more. Then they began the task of replenishing the tanks. But as little had been taken out, this was finished in a very few minutes.

“Now let’s get on,” urged Mr. Lewis. “We want to cover a good many more miles yet before we stop for the noon meal.”

Another hour brought them again to a region of hard soil, and the dromedaries increased their pace several miles per hour.

“Wish it would stay like this all the way,” said Joe, noting that ground was being covered much faster.

“Won’t though. But we’ll have stretches of it here and there.”

As the minutes passed, the glare from the sand became more intense, and the temperature went steadily up. The boys had dark-colored glasses but hesitated to put them on so soon.

“Wouldn’t a good cold drink come in fine now?” asked Bob, keeping his hands off his canteen with difficulty.

“Sure would. But we must fight the temptation to drink too often,” returned Joe. “Remember, we’re on the desert now, and not in the mountains, where there are plenty of springs.”

They rode rapidly on, the country remaining about the same. The red pebbles, however, grew more numerous, some of them glowing like rubies.

Joe remarked that they were gradually ascending, and Bob nodded.

“There’s a line of high dunes over there,” he said, pointing to the distant horizon. “Fekmah said when we reach those we’ll have climbed a good many hundred feet. We should get to them tomorrow.”

In a short time they passed beyond the stretch of hard soil and again plodded through loose sand. From all indications, it was heated to a high degree by the fierce sun. How the dromedaries stood it was a mystery to the boys.

“I wonder how Tishmak can find the way to the Ahaggar Mountains?” mused Joe, glancing up ahead at the guide. “He isn’t using a compass.”

“Does seem strange,” Bob agreed. “But I suppose he’s been over the route so much that he knows all the landmarks by heart, though it looks like a sandstorm or something else would change the surface of the land.”

Mention of the Ahaggars brought to mind the possibilities of finding the hidden riches. Bob and Joe wondered if the two thieves who had caused the explorers so much trouble would, with the aid of the stolen map, locate the treasure first. Perhaps they had already found the place and were gloating over the success of their wicked scheming. The youths said nothing, but the expression on their faces told what they would do to the men if given the opportunity.

“We’ll finally have a chance to square things,” thought Bob, gritting his teeth. “And oh, how those fellows will look when we’re through with them!”

A little later they came to a deep valley between the mounds of sand. In order for the camels to cross it they would find it necessary to climb the steep sides of the dune.

Mr. Lewis rode back to the boys.

“Have to be careful here,” he warned. “It’s rather steep near the top. Don’t let your mounts get out of control.”

The next instant he was on his way back to the front of the caravan.

The climb was hard and not a little dangerous, but the sure-footed dromedaries did not even threaten to slip.

They had barely reached the top when a cry of delight from Joe mingled with the scarcely less emotional exclamations of the others at sight of a small oasis not far away down the opposite slope. A number of tall date palms towered above the green grassy area, an indication that water was to be had for the taking.

“Hurrah!” cried Bob. “Water at last!”

“And if I’m not mistaken, we’ll find dates there, too,” put in Joe.

“You’re right,” affirmed Mr. Lewis, coming up from the side. “And this seems to be a good spot to stop for the noon meal. We’ll have it shady this afternoon when we take our midday rest.”

Nearer and nearer they were coming to the oasis, when suddenly, from behind a low dune of sand, appeared a small caravan of Arabs—possibly bandits.