my boy," was
the rejoinder, "but so far no trace has ever been found of it, and it
is, no doubt, like the lost river of which Pete was telling us, a mere
myth."

"I didn't say it was a miff," protested Pete. "I jes' said I didn't
believe it."

The remainder of that afternoon was spent in making more measurements
and sketches of the interesting mesa, and the boys, on their own
account, conducted a search for a possible entrance to the lost river.
But, as may be supposed, they found none.

"I guess as romance-seekers we are not a success," said Jack, as at
sun-down they prepared to quit. "Just think, what a proud bunch we'd
have been if we could say we--The Border Boys--discovered the lost
river of the mesa dwellers."

"We might be a sorry bunch, too," amended the practical Walt. "I tell
you, Jack, I don't want anything to do with lost rivers, especially
when they are underground."

"Walt, the spirit of adventure is lacking in you," laughed Jack.
"You'd never make a Don Quixote----"

"A donkey who?" asked Walt innocently.

"Oh, you're the limit," chuckled Ralph, going off into a roar of
laughter at the ranch boy's expense.

That evening the animals' pasture was changed to the opposite side of
the mesa, where they could find fresh grass. The camp, however, was
left as it was. After supper watches were assigned, as usual, the
latter part of the night guardianship falling to Coyote Pete and Jack
once more. When, soon after midnight, Walt and Ralph Stetson aroused
them, there was nothing much to report except that One Spot had engaged
in a spirited kicking match with his brethren. Outside of that, all
had been, to quote Walt:

"Quiet along the Mesomac."

"We'll patrol round the whole mesa," said Coyote Pete, as he and Jack
shouldered their rifles, "meeting by the stock on the other side."

After a few words more, the two sentries strode off into the darkness
in different directions, meeting, as arranged, by the stock. Neither
had anything to report, and in this way they kept up the night watch
for an hour or more. They had met for the sixth time by the tents
containing their sleeping comrades, when from the opposite side of the
mesa came a shrill neigh of terror, followed by sounds of wild
galloping and snorting.

"Something's up!" shouted Pete, as, with his rifle in readiness and
followed closely by Jack, he tore around the mesa to ascertain the
cause of the trouble.

As the two sentries emerged