"I guess you are right," answered Alan after long thought; "I don't know what is to be gained by the trouble of a landing at the camp by the lake."

"Nothing but that hot supper," smiled Ned, "and we'll have to put that off a few days, I think."

"All right," agreed Alan, "set your course and with luck we'll do a little treasure hunting before dark."

This being settled, the prow of the Cibola was pointed a little west of northwest, and, dropping to a lower stratum to escape the lively eastern breeze at the higher alt.i.tude, the boys started at last directly for the and arid broken mountains of Northwestern Arizona.

This region, bordering on the great sand dunes lying beyond the Ch.e.l.ly River, was to be the beginning point of their arduous and momentous search. From that place to a point nearly one hundred miles to the southeast lay the secret fastnesses of mountain, canyon and mesa wherein, somewhere, according to the Spanish soldier's record, was the secret city of a dead race and the treasure that had brought Ned and Alan half way across a continent.

What such a search meant one glance at the monotonous and unending rock easily told. On foot, only the compa.s.s could lead a man forward in such wilderness of abrupt heights and winding chasms. As the boys meant to manage it, the attempt had possibilities, but it might mean days of drifting, of watching, of doubling back and forth over every possible site. And that was now their task.

So far as they could, Ned and Alan meant to begin at the extreme northern end of this unknown land and, sailing back and forth from east to west, cover every foot of exposed ground with their powerful gla.s.ses.

Both boys had long since agreed in this conclusion: the "city" meant no more than one large structure similar to but on a larger scale than those found in the Chaco Canyon at the extreme southern end of the Tunit Chas Mountains. This would be indicated now by nothing more than rectangular lines of wall stones, probably in piles, outlining the shape of the "city" or palace. Prominent among these ruins should be the more elevated temple, the object of their search. And beneath this should be found the underground "khivas"

or religious chambers.

That this "city" was secret or hidden was proof to Ned and Alan and Major Honeywell that it would not occupy a prominent place such as an exposed plateau or a high level mesa. Only one other location was left, the ab.u.t.ting shelf of some canyon. And the young navigators had pictured to themselves that, if this should prove to be the location, the shelf would be so elevated as not to be visible from the front or below and that it would be concealed from above by an extended and overhanging cliff.

"Look for it as you would look for a bird's nest in the cliff,"

suggested Ned. And that was the plan of search.

It was nearly three o'clock when the boys had bade farewell to the Arrow and about half past five when the Cibola sailed over the second ridge of the Tunit Chas. But the course was far to the north and there was naturally no sign of the waterfall plateau or Camp Eagle. For a time they thought of pa.s.sing over the camp and dropping a message, but this pleasant idea was given up.

"Although," as Alan expressed it, "one of Elmer's hot suppers and a soft bed of balsam boughs to-night wouldn't be bad."

Ned thought of the four nights of hard floor and agreed, but he said:

"You'll have to forget soft beds if we're ever going to find Cibola.

We'll come down to-night, though, and make a camp of our own with a fire and a pot of coffee, and at daybreak we'll be off."

The boys had taken a light luncheon just after starting on the return trip, and now, soaring over the Tunit Chas again, they began to be anxious for night and supper.

At seven o'clock the peaks and ridges below them had begun to drop into foothills and as the great sandy deserts of distant Utah and nearer by Arizona came before their eyes the boys decided that it was time to anchor for the night. They were sailing over the eastern slope of the last low ranges of hills, barren of trees or vegetation. The aeroplanes being given the proper depression, the Cibola shot earthward and then, the propeller coming to a pause, floated gently along above the jumble of rocks. Making fast the anchor in a ragged pile of these the boys soon drew the Cibola to the ground and lashed her fore and aft to heavy boulders.

The firm ground felt delicious to the tired boys and they refreshed themselves with a brisk race over the open s.p.a.ce between the rock piles. Then came Alan's camp fire, a hot supper and preparations for a good night's rest. There were no pine needles of balsam boughs, but fatigue made a fine mattress, and it was not long before the tired boys, rolled up in their blankets, were fast asleep on the soft sand.

"I hope," said Ned drowsily as they were dropping off to sleep, "that we won't have any Jack Jellups or thieving Utes to-night. My nerves need rest."

Then the boys got eight good hours of health and strength giving sleep in the tonic air of the Arizona Mountains.

CHAPTER XXVI

THE SECRET TUNNEL IN THE MESA

At five o'clock Ned and Alan were astir. With regrets that they were not at Camp Eagle for a plunge in the cool mountain lake, they prepared another hot meal, ate it, and boarded the Cibola.

The balloon had now been inflated thirty-eight hours and was noticeably showing the loss of its gas. While the top of the bag was yet round and firm in the heat of the sun the lower sides had become a trifle flabby as the cool evening had come on. Up to this time all records for balloon flight had been broken a fact due to the renewed buoyancy caused each day by the hot, Southwestern Sun.

And, exploration in and quick ascent from the canyons before them would before long call for the use of ballast. The boys agreed that the time had arrived to utilize their liquid hydrogen. The shrinkage that night had been quite perceptible.

They regretted that but two-thirds of this remained--about eleven cubic feet. This when reconverted meant nearly twelve thousand cubic feet of new gas at their present alt.i.tude. As the work of converting the gas involved care, preparation for it was made before the Cibola was cut loose.

The reconverter, a reduced inversion of the apparatus used in making liquid air, was made ready. When the m.u.f.fled explosions and the heat of the tubes told the boys that the reconverter was working perfectly and pumping new and needed gas into the shrunken Cibola's long bag, the lashings were loosed and once more the faithful dirigible mounted skyward.

With Major Honeywell's map of the region spread out on the deck of the bridge and the binoculars in hand Ned began the long antic.i.p.ated search for the lost city.

All day the process of turning the liquid hydrogen back into buoyant gas went on. And all day the Cibola wound her devious course over the peaks and chasms beneath. By night half the hydrogen jars were empty and Ned and Alan saw the evening close in on them without a sign of the object of their search. When darkness stopped further work the balloon was brought to earth and camp made again.

The following day, as uneventful as the first, gave no indication of the secret city. The rest of the liquid hydrogen was transformed into gas. The sun seemed to enfold the craft in a fiery embrace.

When camp was made again that night the Cibola had been afloat eighty hours.

"I think she is good for another forty-eight hours," said Ned that night. "If we find nothing in two more days we'll have our choice of going out on foot or of quitting in time to pick up Elmer and Bob and make a dash to civilization. What do you say?"

"I don't know," replied Alan, "I'd hate to give up as long as we can fly. I think the boys can care for themselves. Let's stick to it.

We have provisions and there is water in some places."

"Well," answered Ned, "we'll have two more days time in which to decide."

The next morning the Cibola showed plainly that her gas was rapidly escaping. New life was given to the balloon by casting overboard some empty hydrogen casks. The fourth day broke hotter than ever.

In all the wilderness examined by the tired and strained eyes of the searchers, not a human being had been seen--not even a wandering Navajo. This day they began the search with renewed vigor, but with the same monotonous result--miles of hopelessly desert rock and sand beneath them, with a little vegetation now and then, but so sign of Indian remains.

At noon Ned said:

"If we were not in a balloon with a compa.s.s and s.e.xtant I should say we were lost. And if Indians ever lived and died hereabouts they certainly left so signs of their bones."

By six O'clock, with the sun gratefully low, Alan expressed discouragement.

"To-morrow at this time," he said, "if we see no indication of the old palace or city or whatever it was--if it ever was--I think I'll vote to try to find Camp Eagle and get out."

"We'll see to-morrow," answered Ned stoutly.

That night at dark, a landing was made on the ledge of a point of land ending in a rounded cliff pointing south, selected because the place was open to the breeze and cool. The Cibola had approached the height from the west, and the boys believed that the promontory projected from yet higher ground beyond. On those portions of the cliff that they could see there was neither shelf nor projection of any kind. The walls rose almost like cut stone and were apparently about three hundred feet high. As the Cibola was about to descend, Alan, who was taking a last survey from the bridge, called Ned's attention to the fact that even the far side of the supposed promontory was separated from the mountains beyond, and that a chasm at least a half mile wide separated the two heights.

"It's a mesa," replied Ned with renewed enthusiasm, "and it will be a good thing to look over it to-morrow. These high and almost unapproachable islands of rock were favorite dwelling places for the Indians."

"But a temple up here wouldn't be a secret very long," replied Alan.

"We've seen this point all afternoon. It's prominent enough."

"That's so," answered Ned, "but we are here, so let's make a landing and eat, and dream over it."

The balloon had now lost so much gas that a landing was easy, and, tired with four days' profitless search and its strain, the young aeronauts were soon beyond even dreams.

It was with no small alarm that the boys saw, when they awoke with the first rays of the sun, that the car of the Cibola, which had been anch.o.r.ed fore and aft to heaped up rocks during the night, was now resting on the ground. Gas, was rapidly escaping. But fortunately the aeroplanes and propeller had been left properly in a horizontal position and no damage had been done.

The boys knew that by throwing over enough ballast and stores the Cibola could be made good for one more flight, but that probably it would be the last. Therefore, the inevitable seemed forced upon them. They would fortify themselves with a good breakfast, look over the mesa, make one more circling flight and then attempt to find Camp Eagle. While Alan made haste to prepare breakfast, Ned determined first on an examination of the mesa point by daylight.