"Say, is this some kind of a josh?" asked Coyote Pete suspiciously.

"Never more serious in my life," Jack a.s.sured him, and then went on to relate the strange experience that had befallen him when he had poked his head out from under the saddle in the sand-storm.

"If they weren't so enormous, I should say they was horses," said Pete; "but the biggest horses that ever growed never even approached them critters--spooks, er whatever they are."

"There are giants among men," suggested Walt, "why shouldn't there be giants among spooks, too?"

"You get to Halifax with that spook talk," said Coyote Pete scornfully.

"I'll bet my Sunday sombrero that whatever them things is, there's some sore of human mischief back uv it. But what is it? Who put it up?"

"Yes, and what for, and why?" laughed Jack. "I tell you, fellows," he went on, "it's no use of our racking our brains to-night over this.

The best thing we can do is to set a watch. Then, if they come again, we can try a shot at them. If not, why then in the morning we'll make an investigation; eh?"

"Durn good advice," grunted Coyote Pete. "Now, I'd suggest that ther perfusser takes ther fust watch, and----"

"No, no, my dear sir; really, I--I have a cold already. A-hem--ach-oo!"

The man of science, it seemed, had really developed serious bronchial trouble in record time.

"Why, professor," said Jack mischievously, "haven't I heard you say that you'd like a chance to investigate such a phenomenon as this?"

"Hum, yes--yes, my young friend. I may have said so, yes. And any other time I should be only too pleased to--Good Land! what's that?"

With the agility of a gra.s.shopper, the professor had jumped fully three feet, as one of the pack-burros, nosing about behind him, accidentally b.u.t.ted him in the small of his back. The others burst into a roar of laughter, which they could not check. The professor, however, adjusted his spectacles solemnly and looked about him with much dignity.

"I thought I saw a book I had dropped, almost in the fire," he explained glibly, "so I jumped to get it before a hot ember fell on it."

"I had no idea you could jump like that, professor," laughed Jack.

"You should have gone in for athletics at Stonefell."

It was finally decided that Walt and Ralph should stand the first watch, and Coyote Pete and Jack the last part of the night. The professor, after carefully drawing tight the curtain of his tent, "to keep the cold out," as he explained, retired. Soon after, Jack and the cow-puncher also went to bed till the watch should summon them to go on duty in their turn.

But the night pa.s.sed without any reappearance of the strange shapes which had so upset the tranquility of the little camp, and, viewed in the fresh light of a new and glorious day, somehow the affair did not seem nearly so ominous and awe-inspiring as it had the night before.

Breakfast, as you may imagine, was speedily disposed of, and, having seen to the stock, the party started out to explore the mesa itself.

As has been said, the side upon which they had camped the night before was nothing but a sheer cliff. Under the guidance of Coyote Pete, they now set out to encircle the strange precipitous formation. Their hearts beat high, and their eyes shone with an aroused sense of adventure as they strode along.

The professor carried with him a small volume containing a partial translation of the symbols and sign language of the ancient tribe whose domains they were about to invade. Jack had a coil of stout, half-inch manila rope, about two hundred feet in length. Walt Phelps' burden was a shovel, while Ralph Stetson carried an axe. All bore with them their revolvers, and Coyote Pete carried, in addition, a rifle.

"Are you afraid of anything?" the professor had asked him, as he noticed the sun-bronzed plainsman pick up this latter weapon.

"Waal," Pete had rejoined, with a portentous wink at the boys, "you never kin tell in this wale of tears what you're a-goin' up aginst--queer shapes, fer instance."

As they strode along, naturally the subject of the shadowy forms which had alarmed them the night before arose. Jack would have liked to investigate them right then and there, but, after all, he decided with the rest of the party, that an exploration of the mesa was the first thing of importance to be accomplished. And an interesting sight the great abandoned aboriginal beehive, was, as they rounded the inaccessible side and emerged upon the portion which faced toward the northwest.

Pete's recollection had not played him false. There was a rough pathway constructed up its face upon this side, and at the top were three tiers of holes bored in the rock face. These were evidently intended for windows, as a larger aperture was just as evidently meant for a door. The path, which zig-zagged up the face of the mesa was about eight inches in width, not more, at its base, and varied--so far as they could see from below--from that breadth to a foot, as it grew higher.

From the base to the summit the mesa was probably about one hundred and fifty feet in height, the windows not commencing till within twenty feet of the top. Its length at the base was, roughly, three hundred feet, and its thickness varied from three hundred feet or more at the center, to a few feet at each end. Roughly, then, its basic outline was that of an irregular parallelogram, while its profile was that of a flat-topped cone. For some moments the little group stood in silence as they gazed up at the yellowish-gray walls of the once-active mound.

Finally, recovering from their reverie, they set out after Coyote Pete to scale the narrow pathway leading to the summit. But, as the cow-puncher set his feet on the lowermost part of the path, he gave an exclamation of astonishment and pointed downward.

There in the dust was a footprint,--several of them, in fact.

It was a startling discovery in that isolated part of the desert to come upon the traces of human occupancy. Robinson Crusoe on his desert island could not have looked any more astonished at the imprint of the savage's sole, than did Coyote Pete. He stood looking down speechlessly at his discovery, while the others crowded about him, asking a dozen questions at once.

"If the sand-storm had hit this section, we'd been able to form some idee of how long ago them hoofs was planted there," said Pete; "but as it is, ther feller who wondered how ther apple got in ther dumpling didn't hev a harder problem than the nut we've got to crack."

"There must have been several of them," said Jack, who had been gazing in the dust, which lay thick on the pathway to the summit of the mesa.

"A dozen at least," nodded Pete. He tipped back his sombrero and scratched his ruffled hair, fairly at a standstill to account for what they had encountered.

"Mightn't it have been prospectors?" asked Ralph.

"Might hev bin, yes," agreed Pete; "but, fer one thing, my son, prospectors don't usually travel in dozens."

"Hum--that's so," a.s.sented Jack, who at first had greeted Ralph's suggestion eagerly.

"Look here!" cried Ralph suddenly, holding up a glittering object which he had just discerned in the bunch-gra.s.s at the base of the mesa.

"What is it, my boy?" inquired the professor.

Ralph extended the object for their inspection.

"A strange coin," cried Walt.

"Not so blamed strange, either," said Pete, picking it off the boy's palm and examining it. "It's a Mexican peso."

"Then the men who were here were Mexicans?" cried Jack.

"Not so fast, my boy," admonished Pete. "Might as well say that every feller who finds a Canadian dime in his pocket is a Kanuck. Say," he suggested suddenly, "suppose you boys jes' see if you can find any tracks around the base of the mesa."

They scattered and looked carefully about them, but the bunch-gra.s.s grew in quite a broad belt all about, and no footmarks could be discerned. Nor did a careful examination of the gra.s.s show any broken or trampled blades, as would have been the case had ponies been there recently.

"That decides it," announced Pete, after this last fact had been ascertained, "whoever made those foot-marks wasn't here recent, that's a fact. But who could they have been, and what brought them here?"

"Maybe Indians," suggested Ralph sagely.

"Yep, if Indians wore boots, which they don't," grinned Pete, while poor Ralph colored to the roots of his hair over the general laugh that arose at his expense.

"I think," announced the professor finally, "that it would be our best plan to go ahead exploring the mesa. After all, there is nothing here that can hurt us. Those ruffians of Black Ramon's have been driven out of the country, and, anyway, they would not be likely to come here. As for Indians, their reservation is many miles to the north-east.

Whoever was here, was either on a scientific quest, like ourselves, or else unfortunately lost in the desert."

"Jes' ther same," grunted Pete, in a low voice that n.o.body overheard, "I'd like ter know what all this means: Big, shadowy shapes flitting around in ther night, and footsteps here in ther mornin'. It don't look right."

He took a swift glance all about him. In every direction lay the desert--glittering, far-reaching, lonely as the open sea. The only break in the monotony came to the south--on the border--where stretched the rocky, desolate ridge.

"No one wouldn't come here without an object," reasoned Pete to himself, as they began the ascent of the narrow, tortuous trail, "now, what in thunder could that objec' hev bin?"