Long bellowing occasionally reached the aeronef from the herds of buffalo that roamed over the prairie in search of water and pasturage. And when they ceased, the trampling of the grass under their feet produced a dull roaring similar to the rushing of a flood, and very different from the continuous f-r-r-r-r of the screws.

Then from time to time came the howl of a wolf, a fox, a wild cat, or a coyote, the "Canis latrans," whose name is justified by his sonorous bark.

Occasionally came penetrating odors of mint, and sage, and absinthe, mingled with the more powerful fragrance of the conifers which rose floating. through the night air.

At last came a menacing yell, which was not due to the coyote. It was the shout of a Redskin, which no Tenderfoot would confound with the cry of a wild beast.

Chapter X

WESTWARD--BUT WHITHER?

The next day, the 15th of June, about five o'clock in the morning, Phil Evans left his cabin. Perhaps he would today have a chance of speaking to Robur? Desirous of knowing why he had not appeared the day before, Evans addressed himself to the mate, Tom Turner.

Tom Turner was an Englishman of about forty-five, broad in the shoulders and short in the legs, a man of iron, with one of those enormous characteristic heads that Hogarth rejoiced in.

Shall we see Mr. Robur to-day?" asked Phil Evans.

"I don't know," said Turner.

"I need not ask if he has gone out."

"Perhaps he has."

"And when will he come back?"

"When he has finished his cruise."

And Tom went into his cabin.

With this reply they had to be contented. Matters did not look promising, particularly as on reference to the compass it appeared that the "Albatross" was still steering southwest.

Great was the contrast between the barren tract of the Bad Lands passed over during the night and the landscape then unrolling beneath them.

The aeronef was now more than six hundred miles from Omaha, and over a country which Phil Evans could not recognize because he had never been there before. A few forts to keep the Indians in order crowned the bluffs with their geometric lines, formed oftener of palisades than walls. There were few villages, and few inhabitants, the country differing widely from the auriferous lands of Colorado many leagues to the south.

In the distance a long line of mountain crests, in great confusion as yet, began to appear. They were the Rocky Mountains.

For the first time that morning Uncle Prudent and Phil Evans were sensible of a certain lowness of temperature which was not due to a change in the weather, for the sun shone in superb splendor.

"It is because of the "Albatross" being higher in the air," said Phil Evans.

In fact the barometer outside the central deck-house had fallen 540 millimeters, thus indicating an elevation of about 10,000 feet above the sea. The aeronef was at this altitude owing to the elevation of the ground. An hour before she had been at a height of 13,000 feet, and behind her were mountains covered with perpetual snow.

There was nothing Uncle Prudent and his companion could remember which would lead them to discover where they were. During the night the "Albatross" had made several stretches north and south at tremendous speed, and that was what had put them out of their reckoning.

After talking over several hypotheses more or less plausible they came to the conclusion that this country encircled with mountains must be the district declared by an Act of Congress in March, 1872, to be the National Park of the United States. A strange region it was. It well merited the name of a park--a park with mountains for hills, with lakes for ponds, with rivers for streamlets, and with geysers of marvelous power instead of fountains.

In a few minutes the "Albatross" glided across the Yellowstone River, leaving Mount Stevenson on the right, and coasting the large lake which bears the name of the stream. Great was the variety on the banks of this basin, ribbed as they were with obsidian and tiny crystals, reflecting the sunlight on their myriad facets.