their outlines been in the semi-darkness, however, that beyond an impression of their great size, he had no more definite idea of the apparitions. That they were travelling at a tremendous pace was doubtless, for hardly had he sighted them before they vanished, and he could not have had his head out of its shelter for more than a second or so.

While the lad lay in the semi-suffocation of the saddle, his mind revolved the problem, but no explanation that he could think of would fit the case. "Might they not have been wild horses?" he thought.

But no,—these were three times the size of any horse he had ever seen. Besides, their blotty-looking outlines bore no semblance to the form of a horse.

But presently something happened which put the thought of the mysterious shadows out of his mind. The wind began to abate. To be sure, at first it hardly seemed to have diminished its force, but in the course of half an hour or so the party could once more emerge, like so many ostriches, from their sand-piles, and gaze about them.

Very little sand was in the air now, but it was everywhere else. In their eyes, mouths, ears, while, if they shook their heads, a perfect little shower of it fell all about them. The animals, too, struggling to their feet out of the little mounds that had formed around them, were covered with a thick coat of grayish dust. It was a sorry-looking party. With red-rimmed eyes, cracked, parched lips and swollen tongues, they looked as if they had been dragged through a blast furnace.

The sky above them now shone with its brilliant, metallic blue once more, while ahead, the sun was sinking lower. In a short time it would have set, and, as Ralph Stetson, in a choked voice, called for "Water," the same thought flashed across the minds of all of them simultaneously.

If they didn't get water pretty soon, their predicament promised to be a serious one.

An examination of the canteens showed that not much more than a gallon remained. If only they could yet "pick up" the mesa before dark, this would not be so serious a matter, but, situated as they were, it was about as bad as bad could be.

"Waal," said Pete, at length, stroking the last grains of sand out of his bleached moustache, "waal, I reckon we might as well hang fer a sheep as er lamb, anyhow. Ef we don't hit water purty soon, we'll be thirstier yet, so we might as well fill up now."

"Illogical, but sensible," pronounced the professor, leading an eager rush for the water canteens, which were carried on the pack burros.

"Here, hold on; that's enough!" cried Jack, as Ralph Stetson bent over backward with the canteen still at his lips.

"Why, I haven't begun to drink yet," protested Ralph.

"Chaw on a bullet, son," advised Pete. "Thet's highly recommended for the thirst."

"Water suits me better," grumbled Ralph, nevertheless yielding the canteen to Jack. The lad drank sparingly, as did Pete and the others. Ralph, alone, of all the party, appeared not to realize how very precious even the little water that remained might become before long.

Refreshed even by the small quantity they had swallowed of the tepid stuff, they remounted, and Pete clambered up upon his saddle. While his pony stood motionless beneath him, he stood erect upon the leather seat. From this elevation, he scanned the horizon on every side. Far off to the southwest was sweeping a dun-colored curtain—the departing sand-storm, but that was all. Otherwise, the desert was unchanged from its previous aspect.

"Let me hev a look at thet thar compass," said Pete, resuming a sitting posture once more.

Jack extended his wrist.

"The compass is all right, I know," he said confidently.

"And I know that we've bin hitting the right trail," declared Pete. "Last time I come this way was with an old prospector who knew this part of the country well enough to 'pick up' a clump of cactus. If that compass is right, we're headed straight."

"Yes—if," put in the professor. "But are you quite sure it is?"

This was putting the matter in a new light. Not one of the party was so ignorant as not to know that, in the many miles they had traveled, the deflection of the needle, by even the smallest degree, might have meant a disastrous error.

"Why, I—I—how can it help being right?" asked Jack, a little uncertainly.

"Which side have you been carrying your revolver on?" asked the professor.

"Why, you know—on the left side," rejoined Jack, with some surprise.

"And the compass on the left wrist?"

"Yes. Why? Isn't it——"

"No, it ain't!" roared Pete. "I see it all now, perfusser; that thar shootin' iron has bin deflectin' ther needle."

"I fear so," rejoined the professor.

Under his direction, Jack moved the compass into various positions, and at the end of a quarter of an hour they arrived at the startling conclusion that they had travelled perhaps many miles out of their way. The metal of the weapons Jack carried having, as they saw only too clearly now, deflected the needle.

"What an idiot I was not to think of such a possibility!" exclaimed Jack bitterly.

"Not at all, my boy," comforted the professor. "The same thing has happened to experienced sea-captains, and they have navigated many miles off their course before they discovered their error."

"All of which, not bein' at' sea, don't help us any," grunted Pete. "Suppose now, perfusser, that you jes' figger out as well as you kin, how far wrong we hev gone."

"It will be a difficult task, I fear," said the professor.

"It'll be a heap difficulter task, ef we don't hit water purty soon," retorted the cow-puncher.

Thus admonished, Professor Wintergreen divested himself of his weapons, and, taking out a small notebook, began, with the compass before him, to make some calculations. At the end of ten minutes or so, he raised his head.

"Well?" asked Jack eagerly.

"Well," rejoined the professor, "it's not as bad as it might be. We are, according to my reckoning, about twenty-five miles farther to the south than we should be."

He consulted his notebook once more.

"The bearings of the mesa require us to travel in that direction." He indicated a point to the northward of where they were halted.

"And it's twenty-five miles, you say?" asked Pete.

"About that. It may be more, and again it may be less."

"Waal, the less it is, ther better it'll suit yours truly. This stock is jes' about tuckered."

With the professor now bearing the compass, they set out once more, this time taking the direction indicated by the man of science.

"Suppose the professor is wrong?" Ralph whispered to Jack, as they urged their almost exhausted cayuses onward.

Jack shrugged his shoulders.

"What's the use of supposing?" he said.

It was sun-down, and a welcome coolness had begun to be noticeable in the air, when Jack gave a shout and pointed directly ahead of them.

"Look, look!" he cried. "What's that?"

"That" was only a small purplish speck on the far horizon, but it broke the monotony of the sky-line sharply. Coyote Pete scrutinized it with keen eyes for a moment, narrowing his optics till they were mere slits. Then—

"Give me the glasses, perfusser," he requested. Every one in the party knew that their lives, or deaths probably, hung on the verdict of the next few seconds, but Pete's slow drawl was more pronounced and unperturbed than ever. He put the glasses to his eyes as unconcernedly as if he were searching for a bunch of estrays. Presently he lowered them.

"Is—is it——?" began Jack, while the others all bent forward in their saddles, hanging on the rejoinder.

"It is," declared Pete, and he might have said more, but the rest of his words were drowned in a ringing cheer.

CHAPTER III.

A NIGHT ALARM.

"How far distant do you imagine it is?"