Suddenly he stopped short, and caught at the nearest tree-trunk to save himself from falling, for the giddiness returned, and he stood panting, trying to master the horrible sensation by drawing a deeper breath. Then he clung more tightly to the tree, and knew what this sense of vertigo meant; for it was no vapour that had overcome him, but the sensation of the earth heaving beneath his feet, with a strange quivering, as if some vast force were passing, and a dull muttering, as of subterranean thunder, made the tree quiver in his grasp.
A few seconds later, as he waited for a repetition of the earth-tremor, knowing now full well that he had for the first time experienced a couple of earthquake shocks, there came from away in front a deep heavy boom, following a strange rushing sound, evidently from the summit of the volcano—the huge safety-valve from which the pent-up forces of the earth escaped to the open air.
Oliver struggled forward a few yards into a clearer spot, where he could just catch a glimpse of the crater of the mountain, and, as he had expected, there was the great globe-like cloud riven into rags of vapour, while dark-looking bodies were falling in various directions about the summit.
As he gazed, the rain of falling fragments ceased, and the torn-up flecks of cloud seemed to be drawn slowly together again by the currents of air on high, first one and then another coalescing, as the tiny globules of spilt mercury glide one into another, till all are taken up. And it was so here, the mysterious attraction blended the flying vapours into one great whole, which floated above the mouth of the burning mountain.
“And I might have been somewhere on the slope, when that burst of stones was falling,” thought Oliver. “Still, I might climb up a hundred times, and no eruption occur. I’m getting cowardly, instead of being accustomed to the place.”
He smiled to himself as he marked the top of the mountain, and aimed as straight as he could for its side, before plunging again into the bewildering maze of trees, whose wide-spreading foliage made all beneath a subdued shade.
But a dozen steps had not been taken before he stopped short, with his heart beating, and listened eagerly, for a distant shout had fallen upon his ear, coming as he felt sure from behind him, and to the right.
Then there was utter silence for a few seconds, before a second shout arose, to be heard plainly enough, but away to his left.
His heart sank again, and the hope died out. That was no cry uttered by one of his companions, but came from a savage, or some wild beast, which he could not say, but he suspected that it must be from one of the apes of which they had seen specimens that morning.
There it was again, rather a human cry, such as a boy might give vent to in a wood, when calling to his fellows, and a few moments afterwards the sound was repeated.