"I don't like to hear ye say that, Frank," he muttered, uneasily; "an' I kinder reckons as how yer father'll feel oneasy when I tell him what yer up to. 'Cause, I opine, ye wants me to carry thet same news back home; don't ye?"

"Sure," answered the other, laughing. "That's what I meant when I said I was glad we'd met up with you, Hank."

"But ye didn't expect to take a turn thar when ye left home, did ye?" the veteran cowman went on.

"Never entered my head, Hank. Fact is, we weren't thinking of Thunder Mountain up to an hour or two ago, when we ran across Peg Grant, who was in town with his two followers, Spanish Joe and Nick Jennings."

"The wust as ever throwed a leg over leather," muttered Hank, between his teeth. "We been talkin' it over, some o' us boys, an' 'bout kim to the conclusion as how them fellers must be in touch with the Mendoza crowd o' rustlers as draps over the Rio Grande every leetle while, to grab a bunch o' long horns."

"My opinion exactly, Hank," went on Frank. "But listen till I tell you what they are thinking of doing about finding out the secret of Thunder Mountain."

Quickly he related the incident of their meeting Peg, and of his boast.

"They'll never do it, mark me," declared Hank, after he had been put in possession of the main facts. "Thet noise ain't human! I been a-hearin' it for the last forty years, an' I give ye my word it's gittin' wuss right along. The reds believe as how it's the voice of the Great Spirit talkin' to 'em. An' honest now, Frank, thems my sentiments to a dot."

"In other words, Hank, you believe the mountain is haunted, and that anyone bold enough to wander into the unknown country that lies back there is going to get into a peck of trouble?" Frank asked, seriously.

"Reckon as how that kivers the ground purty well," replied the cowman, grimly.

"Well," Frank went on, "we happen to believe something different, and we mean to look into the thing a bit. It wouldn't surprise me to find that some sharp crowd has been taking advantage of the bad name Thunder Mountain has always had, to hide among those canyons. And, Hank, I'm going to look for the trail of some cattle while I'm there!"

"Which I take it to mean," Hank continued thoughtfully, "that you kinder think them rustlers might be usin' the ha'nted mounting for a hiding place to keep the cows which they run away with? Um! wa'al now, I never thort o' that afore. But stands to reason no Mexicans'd ever have the nerve to go whar white cowmen kept away from."

"Not unless they had solved the strange mystery of the mountain, and no longer saw any reason to be afraid of the thunder. But listen while I tell you something else that happened to my friend here."

Frank then described the sudden bolt of Domino. At his first words the experienced western man looked wise. He had immediately guessed what caused the unexpected action of the usually tractable black horse.

"As low down a trick as was ever carried out," he remarked, finally, as he looked at the thorn. "And jest sech as thet sneakin' coyote, Spanish Joe, would be guilty of tryin'. I've seen it done more'n a few times; and twict the critter was rounded up, and treated like he'd been a hoss thief; 'case ye see, in each case 'twar a woman as rid the animile as got the thorn. But ye must let me rub somethin' on thet wound right away, Bob."

"Don't bother," sang out Frank, cheerfully; "because we happened to have with us that ointment you gave me, and I used it a while ago. I'll put on more to-night when we get the saddles off, and once again in the morning."

"Then ye mean to go into camp soon?" inquired Hank.

"See that timber over yonder, where a stream runs? We'll settle down for the night there. Better hold over with us, Hank, unless you're in a terrible hurry to get back home," Frank observed.

"I'd like to fust rate, Frank; and p'raps thar aint no sech great need o' gittin' back to the ranch to-night. Yes, I'll hang over. P'raps I kin coax ye to give up that crazy ijee 'bout Thunder Mounting."

And when they had settled down under the trees, with the westering sun sinking toward the horizon where, in the far distance, Frank pointed out to his chum the towering peak toward which they were bound, old Hank did try to influence his employer's son into giving up his intended trip.

It was useless, however. Frank had made up his mind, and obstacles only served to cause him to shut his teeth more firmly together and stick to his resolution. And so they spent the night very comfortably, under the twinkling stars.

"Tell dad not to worry about us at all, Hank," Frank said to the veteran, on the following morning, as they were bidding him good-bye. "We'll turn up all right in the course of a few days. And perhaps, who knows, we might be able to tell you all about the queer noise that shakes the earth every little while around the big uplift. So-long, Hank!"

The old cowman sat in his saddle, and looked after the two boys as their horses went prancing away, each of the riders turning once or twice to wave a jolly farewell, with uplifted hats.

"As fine a pair o' happy-go-lucky boys as ever drawed breath," Hank muttered, as his eyes followed their vanishing forms beyond the mesquite thicket. "But I sure feel bad 'bout them goin' into that 'ere Thunder Mounting territory. I hopes Mr. Haywood'll start out with a bunch o' cowmen to round 'em up. But he thinks that Frank kin hold his own, no matter what comes along. If he don't show signs o' bein' worried, I'm goin' to see if the overseer, Bart Heminway, won't take the chances of sendin' several of us out to hunt for strays; an' it'll be funny now, how them mavericks all run toward Thunder Mounting."

Chuckling, as if the new idea that had appealed to him gave him considerable satisfaction, the old cow-puncher stirred his little bronco into action, and was soon galloping away. But, more than a few times, he might have been observed to turn in his saddle and cast a look of curiosity, bordering on apprehension, toward the dimly-seen mountain that arose far away on the Southwestern horizon.

For to Hank Coombs that peak stood for everything in the line of mystery and unexplained doings.

CHAPTER IV

A NOTE OF WARNING AT THE SPRING HOLE

"Pull up, Bob; I sure glimpsed something moving, out there in the sage brush!"

Both horses came to an immediate stop as the bridles were drawn taut.

"Which way, Frank?" asked the Kentucky lad, eagerly, as he threw back his shock of black hair, and waited to see where the finger of his companion would point.

"Whatever it was disappeared behind that spur of the low foot hills yonder. I just caught a peep of the last of it. Here, Bob, take the glasses, and wait to see if it shows up again on the other side of the rise," and Frank thrust the binoculars into the hand of his chum.

"Think it could have been a prowling coyote; or perhaps a bunch of antelope feeding on the sweet grass around some spring hole, as you were telling me they do?" asked Bob, holding himself in readiness.

"Well," returned Frank, quickly, "the sun was in my eyes some, you see, and so I wouldn't like to be too sure; but somehow, Bob, I just have a notion that it was a horse."

"With a rider on it, of course!" exclaimed the other lad, as he raised the glasses to his eyes, training them on the further end of the squat elevation that stood up in the midst of the sage level like a great hump on a camel.

"There, looks like I was right, Bob!" ejaculated Frank, a minute or so later, as something came out from behind the low hill, moving steadily onward.

"Indians! as sure as anything!" fell from the lips of the one who held the field glasses to his eyes.

"One—two—three—a heap of the reds in that bunch, I reckon," muttered Frank, watching with his naked eye; although the distance, separating them from the spot where the