He flung a stone, and, as it went spinning downward, it seemed to him that many seconds elapsed before it struck the bottom with a dull thud.

But the tree seemed strong enough to answer every purpose, and capable of bearing a weight much greater than his.

The trunk at the largest part was fully a foot in diameter, and the top extended far enough over the opposite edge to prevent any weakness from the thinning out of the branches.

But what astonished Fred more than anything else, was the discovery that the tree had been felled not, by nature, but by man.  The trunk had been cut through, clearly and evenly, by some sharp instrument, and beyond question had been used as a bridge before.

“Somebody has been here ahead of me,” reflected the lad, as he examined this interesting evidence, “and I don’t believe it was an Indian, either.  I don’t know what could bring a party into this part of the world, but they have been here surely, and if the bridge was good enough for them, it will do for me.”

He was quite certain that he could walk over, after the fashion of Blondin, but it would have been foolhardy in the highest degree, and he adopted the wiser course of putting himself astride of the trunk, and hitching along a few inches at a time.  His rifle interfered somewhat, but he kept up his progress, pausing a few seconds at the centre of the chasm to look down at the bottom far below him.

“Suppose the tree should break,” he exclaimed, in a frightened whisper, “it would be the last of a fellow!  No one could drop down there, and save his neck without a parachute.  I guess the best thing I can do is to get over as soon as I know how—­”

At this juncture, as he was on the point of resuming his onward progress, he noticed a peculiar jar of the log, accompanied by a scratching.  Mis first impression was that it came from behind, but, upon turning his head, could see nothing.  When, however, he looked forward, the terrible explanation at once appeared.

The head or top of the tree was unusually bushy and luxuriant, and, although a considerable time had elapsed since it had been felled, yet there were a great many leaves clinging to the branches—­not enough to afford concealment to any animal fleeing from a hunter.  Then Fred first looked in that direction, he failed to see that one of the most dangerous animals of the Southwest was crouching there.

As he looked inquiringly ahead now, he observed a huge American cougar, larger than that of the night before, issuing from among the branches.  With his phosphorescent eyes fixed upon the terrified lad, he was stealing slowly along the log, giving utterance to a deep guttural growl, separating his lips as he did so, so as to show his long, white, needle-like teeth, intended for the rending of flesh.

For a moment Fred was transfixed at the sight.

The cougar clearly meant fight, and assumed the offensive without a second’s hesitancy.  He seemed to have been crouching in the bushes, and calmly awaited the time when the boy should advance too far to retreat.