Plainly could they see the outlines of trees growing along the verge. But beyond them, nothing. It differed essentially from a canyon, because there was no other side at all. Strain his eye as he might, Stern could detect no opposite wall. And now, realizing something of the possibilities of such a chasm, he swung the Pauillac southward. Flying parallel to the edge of this tremendous barrier, he sought to solve the mystery of its true nature. "If I go higher, perhaps I may be able to get some notion of it," thought he, and swinging up-wind, he spiraled till the barometer showed he had gained another thousand feet. But even this additional view profited him nothing. Half a mile to westward the ragged tree-line still showed as before, with vacancy behind it, and as far as Stern could see to north, to south, it stretched away till the dim blue of distance swallowed it. Yet, straight across the gulf, no land appeared. Only the sky itself was visible there, as calm and as unbroken as in the zenith, yet extending far below where the horizon-line should have been--down, in fact, to where the tree-line cut it off from Stern's vision. The effect was precisely that of coming to the edge of a vast plain, beyond which nothing lay, save space, and peering over. "The end of the world, indeed!" thought the engineer, despite himself. "But what can it mean? What can have happened to the sphere to have changed it like this? Good Heavens, what a marvel--what a catastrophe!" Determined at all hazards to know more of this titanic break or "fault," or whatsoever it might be, he banked again, and now, on a descending slant, veered down toward the lip of the chasm. "Going out over it?" cried Beatrice. He nodded. "It may be miles deep!" "You can't get killed any deader falling a hundred miles than you can a hundred feet!" he shouted back, above the droning racket of the motor. And with a fresh grip on the wheel, head well forward, every sense alert and keen to meet whatever conditions might arise, to battle with cross-currents, "air-holes," or any other vortices swirling up out of those unknown depths, he skimmed the Pauillac fair toward the lip of the monstrous vacancy. Now as they rushed almost above the verge he could see conclusively they were not dealing here with a canyon like the Yosemite or like any other he had ever seen or heard of in the old days. There was positively no bottom to the terrific thing! Just a sheer edge and beyond that--nothing. Nowhere any sign of an opposite bank; nowhere the faintest trace of land. Far, far below, even a few faint clouds showed floating there as if in mid-heaven. The effect was ghastly, unnerving and altogether terrible. Not that Stern feared height. No, it was the unreality of the experience, the inexplicable character of this yawning edge of the world that almost overcame him.