They returned to the rent in the mountain which the explosive had made, and without further hesitation stepped down into the depths below, and Mackay, who was the last to descend, dragged with him a number of empty flour bags with which he effectually screened the little light which filtered between the sundered rocks. All was still in the passage as they felt their way cautiously forward, hugging the walls for guidance, their bare feet plashing in the oozy mire. Mackay and Bob led the way, each pressing against the opposite sides of the passage for support. Jack and the Shadow followed, more secure of their steps, knowing that the way was proved before them. On, on, they struggled; Bob would have dearly liked to light a match, but that would have been extremely foolhardy at such a critical juncture of their pilgrimage, as it would betray their presence to any aboriginal who might happen to be lurking near.
Already they seemed to have been an age in the stifling cavern, though but a few minutes had elapsed since their entry. The tunnel, as nearly as Bob could judge, had continued on a straight course, but it was hard to estimate with certainty how great a distance had been traversed.
Suddenly Mackay stopped and clutched Bob's arm in a vice-like grip.
"There's a hole o' some sort at our feet," he whispered, as the lad stumbled backwards.
Bob put forward one foot gingerly, but it met with no resistance; assuredly a dangerous void intervened in their path. In vain they sought across the full width of the passage for a foothold; not an inch of solid ground remained, and the clayey particles dislodged by their essaying footsteps fell down into an unknown depth, and sundry gurgles and splashes echoed back as they reached the bottom.
"There's no scarcity o' water there," remarked Mackay; then he felt over as far as he could reach with his rifle, and at the utmost limit of his stretch something hard interposed. "It's just like a shaft cutting down through the lode," he murmured; "but how the beggars get across it beats me to understand."
"We could take it at a jump, I think," suggested Jack.
"I'm afraid we'd slip into the water if we tried, my lad. It's no' easy gettin' a firm footing in this clay for a start. No, I think I'll throw the Shadow across first an' he can steady us from the other side."
"Say, boss," said that individual, plaintively, "I ain't no flying machine or human bullet. I reckon my tender bones won't get damaged so much if I jump——"