"I wouldn't have believed," he muttered, "what a shattering influence a night watch has on a man's nerves."
The long wailing cry of a dingo now penetrated piercingly over the desert from the west, and the watcher stirred uneasily at the mournful sound which seemed to convey in it all the sadness and despair of a voice from the nether world.
The weird notes had scarcely died away when he became conscious of a peculiar tap-tapping almost close beside him. He could not make it out; the black surface of the barring range rose before his eyes, but he could distinguish nothing there, and the moon shone clearly on the giant rock. Tap! Tap! Tap! Softly the echoes came but imperceptibly growing louder; anxiously he scanned the bare hillside for some clue to the mystery, and as his eyes reached the ridge of the mountain he was startled to see a tall beshrouded figure standing there, and apparently gazing down upon him. Bob was certain the apparition had not been in the same place but a minute ago, and surely he could not be responsible for these strange noises which seemed to come from the mountain, yet with no cause showing. Tap! Tap! Tap! Harsher and more metallic the ghostly reverberations rang, and now a faint call wafted down from the heights; again and again it came, gently falling on the mystified listener's ears like a voice from the skies, and the strange figure aloft waved his arms in wild gesticulation. Sharper and still sharper sounded the demoralizing tapping, and with it now came a curious shuffling, slight almost to noiselessness, but Bob's sensitive ears were not to be deceived. A cold sweat broke out upon his brow; the vague disturbances of the night were issuing not from the side of the mountain, but from its interior! With a quick stride he reached Mackay, and at a touch the sleeper awoke.
"What is it, lad, what is it?" he asked, breathlessly, his rifle already in his hand.
Bob placed his finger on his lips, and pointed silently to the mountain.
"They're coming through it!" he whispered, hoarsely.
Mackay nodded briefly, and strode silently over to the resounding wall, and Bob hastily aroused the sleepers. In a moment the camp was prepared, and meanwhile Mackay was walking stealthily along the base of the mount, his ears bent down to the rock as he strove to locate the mysterious alarms. And now the distant call from the hilltop floated down to them once more, and Emu Bill started at the sound, and looked up wonderingly, for the faint double note of a coo-ee had this time been plainly heard, and the tall form on the distant heights was despairingly pointing outwards across the desert.
"That nigger can coo-ee like a good 'un," muttered he, "an' he's tryin' to warn us. I reckon that's because we didn't shoot him to-day; but I never believed a nig could feel any gratitood."
Suddenly the echoes ceased, and all was silent as a tomb. Bob looked, and saw Mackay crouched hard against the rocky wall on the edge of a deep fissure which showed down half the face of the mountain. He seemed like an animal preparing for a deadly spring.
"I reckon we should go over beside him," said Never Never Dave, but so speedy had been the developments of events that there was no time to decide upon a definite course of action. Indeed, not one of the party guessed what wild happening was about to take place. Bob somehow expected to hear the preliminary yells of an attacking horde, even as they had heard them before, but no such outcry took place. He saw Mackay beckon wildly with one hand over his shoulder, and quickly he obeyed the summons, the others following with silent footsteps. Then a stone clattered noisily at the bottom of the ravine, and to Bob's amazement, a swarthy face appeared from the depths, surmounted by a tall waving head-dress of feathers. As the warrior emerged further into view, Bob's astonishment increased, for here was no naked savage, but a gorgeously arrayed aboriginal, splendidly proportioned, and carrying in his hand a long curved bow and several arrows. Bob had just time to note this much and no more, for Mackay's rifle belched out almost in the new arrival's face, but the shot had been fired with the hands resting loosely on the ground, and the bullet sped high, scattering the nodding plumes of the astonished black in all directions. With a cry of pent-up fury, Mackay lunged forward to grasp his prey, and at once the stalwart native closed with him. And now crowding up behind, one by one, a solemn procession of similarly attired warriors came trooping. The first of the number without hesitation rushed to the assistance of his struggling comrade, the others calmly bore down upon the little group, who, with Bob at their head, had watched the scene as in a dream. With a hoarse snarl of rage Never Never Dave opened fire, and almost at the same instant the entire artillery of the camp spouted out flame and smoke and leaden hail. In reply, a cloud of arrows flew about their heads, and Bob felt one pierce the muscle of his arm, but he pulled out the slender barb with a wrench, and again his rifle spoke, and the roar of many reports in his ears told him that his comrades too were strenuously engaged. Backwards and forwards the spectral warriors surged, and yet never a sound escaped their lips, and they strove with steady effort to come to close quarters with the camp defenders.