On the surface of the ground or through the swaying branches of the trees the spoor of man or beast was an open book to the ape-man, but even his acute senses were baffled by the spoorless trail of the airship. Of what good were eyes, or ears, or the sense of smell in following a thing whose path had lain through the shifting air thousands of feet above the tree tops? Only upon his sense of direction could Tarzan de-pend in his search for the fallen plane. He could not even judge accurately as to the distance it might lie from him, and he knew that from the moment that it disappeared beyond the hills it might have traveled a considerable distance at right angles to its original course before it crashed to earth. If its occupants were killed or badly injured the ape-man might search futilely in their immediate vicinity for some time be-fore finding them.
There was but one thing to do and that was to travel to a point as close as possible to where he judged the plane had landed, and then to follow in ever-widening circles until he picked up their scent spoor. And this he did.
Before he left the valley of plenty he made several kills and carried the choicest cuts of meat with him, leaving all the dead weight of bones behind. The dense vegetation of the jungle terminated at the foot of the western slope, growing less and less abundant as he neared the summit beyond which was a sparse growth of sickly scrub and sunburned grasses, with here and there a gnarled and hardy tree that had withstood the vicissitudes of an almost waterless existence.
From the summit of the hills Tarzan's keen eyes searched the arid landscape before him. In the distance he discerned the ragged tortuous lines that marked the winding course of the hideous gorges which scored the broad plain at intervals -- the terrible gorges that had so nearly claimed his life in punish-ment for his temerity in attempting to invade the sanctity of their ancient solitude.
For two days Tarzan sought futilely for some clew to the whereabouts of the machine or its occupants. He cached por-tions of his kills at different points, building cairns of rock to mark their locations. He crossed the first deep gorge and cir-cled far beyond it. Occasionally he stopped and called aloud, listening for some response but only silence rewarded him --a sinister silence that his cries only accentuated.
Late in the evening of the second day he came to the well-remembered gorge in which lay the clean-picked bones of the ancient adventurer, and here, for the first time, Ska, the vul-ture, picked up his trail. "Not this time, Ska," cried the ape-man in a taunting voice, "for now indeed is Tarzan Tarzan.
Before, you stalked the grim skeleton of a Tarmangani and even then you lost. Waste not your time upon Tarzan of the Apes in the full of his strength. But still Ska, the vulture, circled and soared above him, and the ape-man, notwithstanding his boasts, felt a shudder of apprehension. Through his brain ran a persistent and doleful chant to which he involuntarily set two words, repeated over and over again in horrible mo-notony: "Ska knows! Ska knows!" until, shaking himself in anger, he picked up a rock and hurled it at the grim scav-enger.
Lowering himself over the precipitous side of the gorge Tar-zan half clambered and half slid to the sandy floor beneath.
He had come upon the rift at almost the exact spot at which he had clambered from it weeks before, and there he saw, just as he had left it, just, doubtless, as it had lain for centuries, the mighty skeleton and its mighty armor.
As he stood looking down upon this grim reminder that an-other man of might had succumbed to the cruel powers of the desert, he was brought to startled attention by the report of a firearm, the sound of which came from the depths of the gorge to the south of him, and reverberated along the steep walls of the narrow rift.
