It was Miss Craigmiles herself who gave Ballard the exact date of Professor Gardiner's coming; driving down to the construction camp alone in the little motor-car for that avowed purpose.

A cloud-burst in the main range had made the stage road from Alta Vista impassable for the moment, leaving the Arcadia Company's railroad—by some unexplained miracle of good fortune—unharmed. Hence, unless the expected guest could be brought over from Alta Vista on the material train, he would be indefinitely detained on the other side of the mountain. Miss Elsa came ostensibly to beg a favour.

"Of course, I'll send over for him," said Ballard, when the favour had been named. "Didn't I tell you he is going to be my guest?"

"But he isn't," she insisted, playfully. Bromley was out and at work, Wingfield had entirely recovered from the effects of his electric shock, and there had been no untoward happenings for three peaceful weeks. Wherefore there was occasion for light-heartedness.

Ballard descended from the bungalow porch and arbitrarily stopped the buzzing engines of the runabout by cutting out the batteries. "This is the first time I've seen you for three weeks," he asserted—which was a lover's exaggeration. "Please come up and sit on the porch. There is any number of things I want to say."

"Where is Mr. Bromley?" she asked, making no move to leave the driving-seat.

"He is out on the ditch survey—luckily for me. Won't you please 'light and come in?—as we say back in the Blue-grass."

"You don't deserve it. You haven't been near us since Mr. Bromley went back to work. Why?"

"I have been exceedingly busy; we are coming down the home-stretch on our job here, as you know." The commonplace excuse was the only one available. He could not tell her that it was impossible for him to accept further hospitalities at Castle 'Cadia.

"Mr. Bromley hasn't been too busy," she suggested.

"Bromley owes all of you a very great debt of gratitude."

"And you do not, you would say. That is quite true. You owe us nothing but uncompromising antagonism—hatred, if you choose to carry it to that extreme."

"No," he returned gravely. "I can't think of you and of enmity at the same moment."

"If you could only know," she said, half absently, and the trouble shadow came quickly into the backgrounding depths of the beautiful eyes. "There is no real cause for enmity or hatred—absolutely none."

"I am thinking of you," he reminded her, reverting to the impossibility of associating that thought with the other.

"Thank you; I am glad you can make even that much of a concession. It is more than another would make." Then, with the unexpectedness which was all her own: "I am still curious to know what you did to Mr. Wingfield: that day when he so nearly lost his life in the laboratory?"

"At what time in that day?" he asked, meaning to dodge if he could.

"You know—when you had him here in your office, with Jerry and Mr. Bromley."

"I don't remember all the things I did to him, that day and before it. I believe I made him welcome—when I had to. He hasn't been using his welcome much lately, though."

"No; not since that day that came near ending so terribly. I'd like to know what happened."

"Nothing—of any consequence. I believe I told you that Wingfield was boring us with the plot of a new play."

"Yes; and you said you couldn't remember it."

"I don't want to remember it. Let's talk of something else. Is your anxiety—the trouble you refuse to share with me—any lighter?"

"No—yes; just for the moment, perhaps."

"Are you still determined not to let me efface it for you?"

"You couldn't; no one can. It can never be effaced."

His smile was the man's smile of superior wisdom.

"Don't we always say that when the trouble is personal?"

She ignored the query completely, and her rejoinder was totally irrelevant—or it seemed to be.

"You think I came down here to ask you to send over to Alta Vista for Professor Gardiner. That was merely an excuse. I wanted to beg you once again to suspend judgment—not to be vindictive."

Again he dissimulated. "I'm not vindictive: why should I be?"

"You have every reason; or, at least, you believe you have." She leaned over the arm of the driving-seat and searched his eyes pleadingly: "Please tell me: how much did Mr. Wingfield find out?"

It was blankly impossible to tell her the hideous truth, or anything remotely approaching it. But his parrying of her question was passing skilless.

"Not being a mind-reader, I can't say what Wingfield knows—or thinks he knows. Our disagreement turned upon his threat to make literary material out of—well, out of matters that were in a good measure my own private and personal affairs."

"Oh; so there was a quarrel? That is more than you were willing to admit a moment ago."

"You dignify it too much. I believe I called him an ass, and he called me an idiot. There was no bloodshed."

"You are jesting again. You always jest when I want to be serious."

"I might retort that I learned the trick of it from you—in the blessed days that are now a part of another existence."

"Oh!" she said; and there was so much more of distress than of impatience in the little outcry that he was mollified at once.

"I'm going to crank the engines and send you home," he asseverated. "I'm not fit to talk to you to-day." And he started the engines of the motor-car.

She put a dainty foot on the clutch-pedal. "You'll come up and see me?" she asked; adding: "Some time when you are fit?"

"I'll come when I am needed; yes."

He walked beside the slowly moving car as she sent it creeping down the mesa hill on the brakes. At the hill-bottom turn, where the camp street ended and the roundabout road led off to the temporary bridge, she stopped the car. The towering wall of the great dam, with its dotting of workmen silhouetted black against the blue of the Colorado sky, rose high on the left. She let her gaze climb to the summit of the huge dike.

"You are nearly through?" she asked.

"Yes. Two other weeks, with no bad luck, will see us ready to turn on the water."

She was looking straight ahead again.

"You know what that means to us at Castle 'Cadia?—but of course you do."

"I know I'd rather be a 'mucker' with a pick and shovel out yonder in the ditch than to be the boss here when the spillway gates are closed at the head of the cut-off tunnel. And that is the pure truth."

"This time I believe you without reservation, Breckenridge—my friend." Then: "Will Mr. Pelham come out to the formal and triumphal opening of the Arcadian Irrigation District?"

"Oh, you can count on that—with all the trimmings. There is to be a demonstration in force, as Major Blacklock would say; special trains from Denver to bring the crowd, a barbecue dinner, speeches, a land-viewing excursion over the completed portion of the railroad, and fireworks in the evening while the band plays 'America.' You can trust Mr. Pelham to beat the big drum and to clash the cymbals vigorously and man-fashion at the psychological instant."

"For purely commercial reasons, of course? I could go a step further and tell you something else that will happen. There will be a good many transfers of the Arcadia Company's stock at the triumphal climax."

He was standing with one foot on the car step and his hands buried in the pockets of his short working-coat. His eyes narrowed to regard her thoughtfully.

"What do you know about such things?" he demurred. "You know altogether too much for one small bachelor maid. It's uncanny."

"I am the cow-punching princess of Arcadia, and Mr. Pelham's natural enemy, you must remember," she countered, with a laugh that sounded entirely care-free. "I could tell you more about the stock affair. Mr. Pelham has been very liberal with his friends in the floating of this great and glorious undertaking—to borrow one of his pet phrases. He has placed considerable quantities of the Arcadia Company's stock among them at merely nominal prices, asking only that they sign a 'gentlemen's agreement' not to resell any of it, so that my father could get it. But there is a wheel within that wheel, too. Something more than half of the nominal capitalisation has been reserved as 'treasury stock.' When the enthusiasm reaches the proper height, this reserved stock will be put upon the market. People will be eager to buy it—won't they?—with the work all done, and everything in readiness to tap the stream of sudden wealth?"

"Probably: that would be the natural inference."

"I thought so. And, as the company's chief engineer, you could doubtless get in on the 'ground floor' that Mr. Pelham is always talking about, couldn't you?"

The question was one to prick an honest man in his tenderest part. Ballard was hurt, and his face advertised it.

"See here, little girl," he said, flinging the formalities to the winds; "I am the company's hired man at the present moment, but that is entirely without prejudice to my convictions, or to the fact that some day I am going to marry you. I hope that defines my attitude. As matters stand, Mr. Pelham couldn't hand me out any of his stock on a silver platter!"

"And Mr. Bromley?"

"You needn't fear for Loudon; he isn't going to invest, either. You know very well that he is in precisely the same boat that I am."

"How shocking!" she exclaimed, with an embarrassed little laugh. "Is Mr. Bromley to marry your widow? Or are you to figure as the consolation prize for his widow? Doubtless you have arranged it amicably between you."

Having said the incendiary thing, he brazened it out like a man and a lover.

"It's no joke. I suppose I might sidestep, but I sha'n't. You know very well that Bromley is in love with you—up to his chin, and I'm afraid you have been too kind to him. That is a little hard on Loudon, you know—when you are going to marry some one else. But let that rest, and tell me a little more about this stock deal. Why should there be a 'gentlemen's agreement' to exclude your father? To a rank outsider like myself, Arcadia Irrigation would seem to be about the last thing in the world Colonel Adam Craigmiles would want to buy."

"Under present conditions, I think it is," she said. "I shouldn't buy it now."

"What would you do, O wise virgin of the market-place?"

"I'd wait patiently while the rocket is going up; I might even clap my hands and say 'Ah-h-h!' with the admiring multitude. But afterward, when the stick comes down, I'd buy every bit of Arcadia Irrigation I could find."

Again he was regarding her through half-closed eyelids.

"As I said before, you know too much about such things—altogether too much." He said it half in raillery, but his deduction was made seriously enough. "You think your father will win his law-suit and so break the market?"

"No; on the contrary, I'm quite sure he will be beaten. I am going, now. Don't ask me any more questions: I've said too much to the company's engineer, as it is."

"You have said nothing to the company's engineer," he denied. "You have been talking to Breckenridge Ballard, your future——"

She set the car in motion before he could complete the sentence, and he stood looking after it as it shot away up the hills. It was quite out of sight, and the sound of its drumming motor was lost in the hoarse grumbling of the river, before he began to realise that Elsa's visit had not been for the purpose of asking him to send for Gardiner, nor yet to beg him not to be vindictive. Her real object had been to warn him not to buy Arcadia Irrigation. "Why?" came the unfailing question, shot-like; and, like all the others of its tribe, it had to go unanswered.

It was two days later when Gardiner, the assistant professor of geology, kept his appointment, was duly met at Alta Vista by Ballard's special engine and a "dinkey" way-car, and was transported in state to the Arcadian fastnesses. Ballard had it in mind to run down the line on the other engine to meet the Bostonian; but Elsa forestalled him by intercepting the "special" at Ackerman's with the motor-car and whisking the guest over the roundabout road to Castle 'Cadia.

Gardiner walked down to the construction camp at Elbow Canyon bright and early the following morning to make his peace with Ballard.

"Age has its privileges which youth is obliged to concede, Breckenridge, my son," was the form his apology took. "When I learned that I might have my visit with you, and still be put up at the millionaire hostelry in the valley above, I didn't hesitate a moment. I am far beyond the point of bursting into enthusiastic raptures over a bunk shake-down in a camp shanty, steel forks, tin platters, and plum-duff, when I can live on the fat of the land and sleep on a modern mattress. How are you coming on? Am I still in time to be in at the death?"

"I hope there isn't going to be any death," was the laughing rejoinder. "Because, in the natural sequence of things, it would have to be mine, you know."

"Ah! You are tarred a little with the superstitious stick, yourself, are you? What was it you said to me about 'two sheer accidents and a commonplace tragedy'? You may remember that I warned you, and the event proves that I was a true prophet. I predicted that Arcadia would have its shepherdess, you recollect."

Thus, with dry humour, the wise man from the East. But Ballard was not prepared at the moment for a plunge into the pool of sentiment with the mildly cynical old schoolman for a bath-master, and he proposed, as the readiest alternative, a walking tour of the industries.

Gardiner was duly impressed by the industrial miracles, and by the magnitude of the irrigation scheme. Also, he found fitting words in which to express his appreciation of the thoroughness of Ballard's work, and of the admirable system under which it was pressing swiftly to its conclusion. But these matters became quickly subsidiary when he began to examine the curious geological formation of the foothill range through which the river elbowed its tumultuous course.

"These little wrinklings of the earth's crust at the foot of the great mountain systems are nature's puzzle-pieces for us," he remarked. "I foresee an extremely enjoyable vacation for me—if you have forgiven me to the extent of a snack at your mess-table now and then, and a possible night's lodging in your bungalow if I should get caught out too late to reach the millionaire luxuries of Castle 'Cadia."

"If I haven't forgiven you, Bromley will take you in," laughed Ballard. "Make yourself one of us—when you please and as you please. The camp and everything in it belongs to you for as long as you can persuade yourself to stay."

Gardiner accepted the invitation in its largest sense, and the afternoon of the same day found him prowling studiously in the outlet canyon with hammer and specimen-bag; a curious figure of complete abstraction in brown duck and service leggings, overshadowed by an enormous cork-lined helmet-hat that had been faded and stained by the sun and rains of three continents. Ballard passed the word among his workmen. The absent-minded stranger under the cork hat was the guest of the camp, who was to be permitted to go and come as he chose, whose questions were to be answered without reserve, and whose peculiarities, if he had any, were to pass unremarked.

With the completion of the dam so near at hand, neither of the two young men who were responsible for the great undertaking had much time to spare for extraneous things. But Gardiner asked little of his secondary hosts; and presently the thin, angular figure prowling and tapping at the rocks became a familiar sight in the busy construction camp. It was Lamoine, the camp jester, who started the story that the figure in brown canvas was a mascot, imported specially by the "boss" to hold the "hoodoo" in check until the work should be done; and thereafter the Boston professor might have chipped his specimens from the facing stones on the dam without let or hindrance.

The masons were setting the coping course on the great wall on a day when Gardiner's studious enthusiasm carried him beyond the dinner-hour at Castle 'Cadia and made him an evening guest in the engineer's adobe; and in the after-supper talk it transpired that the assistant in geology had merely snatched a meagre fortnight out of his work in the summer school, and would be leaving for home in another day or two.

Both of the young men protested their disappointment. They had been too busy to see anything of their guest in a comradely way, and they had been looking forward to the lull in the activities which would follow the opening celebration and promising themselves a more hospitable entertainment of the man who had been both Mentor and elder brother to them in the Boston years.

"You are not regretting it half as keenly as I am," the guest assured them. "Apart from losing the chance to thresh it out with you two, I have never been on more fascinatingly interesting geological ground. I could spend an entire summer among these wonderful hills of yours without exhausting their astonishing resources."

Ballard made allowances for scholastic enthusiasm. He had slighted geology for the more strictly practical studies in his college course.

"Meaning the broken formations?" he asked.

"Meaning the general topsyturvyism of all the formations. Where you might reasonably expect to find one stratum, you find others perhaps thousands of years older—or younger—in the geological chronology. I wonder you haven't galvanised a little enthusiasm over it: you discredit your alma mater and me when you regard these marvellous hills merely as convenient buttresses for your wall of masonry. And, by the way, that reminds me: neither of you two youngsters is responsible for the foundations of that dam; isn't that the fact?"

"It is," said Bromley, answering for both. Then he added that the specifications called for bed-rock, which Fitzpatrick, who had worked under Braithwaite, said had been uncovered and properly benched for the structure.

"'Bed-rock,'" said the geologist, reflectively. "That is a workman's term, and is apt to be misleading. The vital question, under such abnormal conditions as those presenting themselves in your canyon, is, What kind of rock was it?"

Bromley shook his head. "You can't prove it by me. The foundations were all in before I came on the job. But from Fitzpatrick's description I should take it to be the close-grained limestone."

"H'm," said Gardiner. "Dam-building isn't precisely in my line; but I shouldn't care to trust anything short of the granites in such a locality as this."

"You've seen something?" queried Ballard.

"Nothing immediately alarming; merely an indication of what might be. Where the river emerges from your cut-off tunnel below the dam, it has worn out a deep pit in the old bed, as you know. The bottom of this pit must, in the nature of things, be far below the foundations of the masonry. Had you thought of that?"

"I have—more than once or twice," Ballard admitted.

"Very well," continued the Master of the Rocks; "that circumstance suggests three interrogation points. Query one: How has the diverted torrent managed to dig such a deep cavity if the true primitives—your workman's 'bed-rock'—under-lie its channel cutting? Query two: What causes the curious reverberatory sound like distant thunder made by the stream as it plunges into this pit—a sound suggesting subterranean caverns? Query three—and this may be set down as the most important of the trio: Why is the detritus washed up out of this singular pot-hole a friable brown shale, quite unlike anything found higher up in the bed of the stream?"

The two young men exchanged swift glances of apprehension. "Your deductions, Professor?" asked Bromley, anxiously.

"Now you are going too fast. True science doesn't deduce: it waits until it can prove. But I might hazard a purely speculative guess. Mr. Braithwaite's foundation stratum—your contractor's 'bed-rock'—may not be the true primitive; it may in its turn be underbedded by this brown shale that the stream is washing up out of its pot-hole."

"Which brings on more talk," said Ballard, grappling thoughtfully with the new perplexities forming themselves upon Gardiner's guess.

"Decidedly, one would say. Granting my speculative answer to Query Number Three, the Arcadia Company's dam may stand for a thousand years—or it may not. Its life may possibly be determined in a single night, if by any means the water impounded above it should find its way through Fitzpatrick's 'bed-rock' to an underlying softer stratum."

Ballard's eyes were fixed upon a blue-print profile of Elbow Canyon pinned upon the wall, when he said: "If that pot-hole, or some rift similar to it, were above the dam instead of below it, for example?"

"Precisely," said the geologist. "In five minutes after the opening of such an underground channel your dam might be transformed into a makeshift bridge spanning an erosive torrent comparable in fierce and destructive energy, to nothing milder than a suddenly released Niagara."

Silence ensued, and afterward the talk drifted to other fields; was chiefly reminiscent of the younger men's university years. It was while Bromley and Gardiner were carrying the brunt of it that Ballard got up and went out. A few minutes later the out-door stillness of the night was shattered by the sharp crack of a rifle, and other shots followed in quick succession.

Bromley sprang afoot at the first discharge, but before he could reach the door of the adobe, Ballard came in, carrying a hatful of roughly crumbled brown earth. He was a little short of breath, and his eyes were flashing with excitement. Nevertheless, he was cool enough to stop Bromley's question before it could be set in words.

"It was only one of the colonel's Mexican mine guards trying a little rifle practice in the dark," he explained; and before there could be any comment: "I went out to get this, Gardiner"—indicating the hatful of earth. "It's a sample of some stuff I'd like to have you take back to Boston with you for a scientific analysis. I've got just enough of the prospector's blood in me to make me curious about it."

The geologist examined the brown earth critically; passed a handful of it through his fingers; smelled it; tasted it.

"How much have you got of this?" he asked, with interest palpably aroused.

"Enough," rejoined the Kentuckian, evasively.

"Then your fortune is made, my son. This 'stuff,' as you call it, is the basis of Colonel Craigmile's millions. I hope your vein isn't a part of his."

Again Ballard evaded the implied question. "What do you know about it, Gardiner? Have you ever seen any of it before?"

"I have, indeed. More than that, I have 'proved up' on it, as your Western miners say of their claims. A few evenings ago we were talking of expert analyses—the colonel and young Wingfield and I—up at the house of luxuries, and the colonel ventured to wager that he could stump me; said he could give me a sample of basic material carrying fabulous values, the very name of which I wouldn't be able to tell him after the most exhaustive laboratory tests. Of course, I had to take him up—if only for the honour of the Institute—and the three of us went down to his laboratory. The sample he gave me was some of this brown earth."

"And you analysed it?" inquired Ballard with eagerness unconcealed.

"I did; and won a box of the colonel's high-priced cigars, for which, unhappily, I have no possible use. The sample submitted, like this in your hat, was zirconia; the earth-ore which carries the rare metal zirconium. Don't shame me and your alma mater by saying that this means nothing to you."

"You've got us down," laughed Bromley. "It's only a name to me; the name of one of the theoretical metals cooked up in laboratory experiments. And I venture to say it is even less than that to Breckenridge."

"It is a very rare metal, and up to within a few years has never been found in a natural state or produced in commercial quantities," explained the analyst, mounting and riding his hobby with apparent zest. "A refined product of zirconia, the earth itself, has been used to make incandescent gas-mantles; and it was M. LÉoffroy, of Paris, who discovered a method of electric-furnace reduction for isolating the metal. It was a great discovery. Zirconium, which is exceedingly dense and practically irreducible by wear, is supplanting iridium for the pointing of gold pens, and its value for that purpose is far in excess of any other known substance."

"But Colonel Craigmiles never ships anything from his mine, so far as any one can see," Ballard cut in.

"No? It isn't necessary. He showed us his reduction-plant—run by water-power from the little dam in the upper canyon. It is quite perfect. You will understand that the actual quantity of zirconium obtained is almost microscopic; but since it is worth much more than diamonds, weight for weight, the plant needn't be very extensive. And the fortunate miner in this instance is wholly independent of the transportation lines. He can carry his output to market in his vest pocket."

After this, the talk, resolutely shunted by Ballard, veered aside from Arcadian matters. Later on, when Bromley was making up a shake-down bed in the rear room for the guest, the Kentuckian went out on the porch to smoke. It was here that Bromley found him after the Bostonian had been put to bed.

"Now, then, I want to know where you got that sample, Breckenridge?" he demanded, without preface.

Ballard's laugh was quite cheerful.

"I stole it out of one of the colonel's ore bins at the entrance of the mine over yonder."

"I thought so. And the shots?"

"They were fired at me by one of the Mexican night guards, of course. One of them hit the hat as I was running away, and I was scared stiff for fear Gardiner's sharp old eyes would discover the hole. I'm right glad for one thing, Loudon; and that is that the mine is really a mine. Sometimes I've been tempted to suspect that it was merely a hole in the ground, designed and maintained purely for the purpose of cinching the Arcadia Company for damages."

Bromley sat up straight and his teeth came together with a little click. He was remembering the professor's talk about the underlying shales, and a possible breach into them above the dam when he said: "Or to—" but the sentence was left unfinished. Instead, he fell to reproaching Ballard for his foolhardiness.

"Confound you, Breckenridge! you haven't sense enough to stay in the house when it's raining out-of-doors! The idea of your taking such reckless chances on a mere whiff of curiosity! Let me have a pipeful of that tobacco—unless you mean to hog that, too—along with all the other risky things."