Mackay shook his head. "I shouldna wonder if it is an extinct volcano," he said; "but there was no lava flow that I remember, and it disappeared just the same."
Notwithstanding the odd happenings during the last few minutes, the camels were not permitted to slacken their pace. Each and all of the party had determined to probe the mystery to the fullest, and the solution was soon forthcoming. As they forced their way into the densest depths of the ghost-like curtain, they became quickly aware of a gurgling, boiling sound almost at their feet. Bob's keen ears were the first to catch the unwonted echoes; but before he could speak a greenish-yellow cloud rolled before his eyes, and he staggered back, choking wildly.
"Ease off, boys," spoke Mackay. "We must scout around an' investigate before we go further."
The whole party, camels and all, were now enveloped in the wreathing smoke-columns, and the sky was hidden from sight. Blindly Bob made a few steps forward, keeping well to the right of the unseen caldron, which now bubbled and foamed spasmodically. The Shadow followed, stumbling and gasping, and within a minute the two found themselves in a clear and untainted atmosphere, and but a yard or so from the base of the gloomy mountain. Loudly they shouted to their companions, and soon the spectral forms of the camels hove into view, with Mackay and Jack treading cautiously at their head. But where were Emu Bill and Never Never Dave? They seemed to have vanished completely.
"They were alongside Jack an' me a minute ago," said Mackay, gazing wonderingly around.
"I reckon I'll go back an' see if they've stopped to look at the scenery," grunted the Shadow; and he made a dash into the heavy fumes once more.
The three who waited by the camels heard a startled cry, followed by a faint splash, then all was silent. Hastily Mackay seized a camel pack-rope, and would have rushed off after him, but Bob interfered.
"I think I can guess where to find them," he said. "Let me go."
With reluctance Mackay saw him depart; but before Bob had entered the chaos the swelling mass rose before him, disclosing in his track a broad, pit-like cavity. Hurriedly he strode to the edge of the caldron; but ere he reached it the Shadow climbed out of its seething depths wet and dripping, and saying strange things to himself. Immediately behind him Never Never Dave's head popped up, and an eloquent flow of language was let loose upon the air. Lastly, Emu Bill scrambled into the open. He looked savagely around for a moment, until he caught sight of the Shadow, and his wrath overflowed in a torrent of abuse. All three were bedraggled enough looking specimens; but the last arrivals were considerably worse off than the Shadow in that respect—their hair was covered with a greenish scum, which spread down over their faces and almost blinded them.