"Let's look sheer down," said the girl. "By lying flat and peering over, there can't be any danger."

"All right, but only on condition that I keep tight hold of you!"

Cautiously they lay down and worked their way to the edge. The engineer circled Beta's supple waist with his arm.

"Steady, now!" he warned. "When you feel giddy, let me know, and we'll go back."

The effect of the chasm, from the very edge of the rock, was terrifying. It was like nothing ever seen by human eyes. Peering down into the Grand Canyon of the Colorado would have been child's play beside it. For this was no question of looking down a half-mile, a mile, or even five, to some solid bottom.

Bottom there was none--nothing save dull purple haze, shifting vapors, and an unearthly dim light which seemed to radiate upward as though the sun's rays, reflected, were striving to beat up again.

"There must be miles and miles of air below us," said Stern, "to account for this curious light-effect. Air, of course, will eventually cut off the vision. Given a sufficiently thick layer, say a few hundred miles, it couldn't be seen through. So if there _is_ a bottom to this place, be it one hundred or even five hundred miles down, of course we couldn't see it. All we could see would be the air, which would give this sort of blue effect."

"Yes; but in that case how can we see the sun, or the moon, or stars?"

"Light from above only has to pierce forty or fifty miles of really dense air. Above that height it's excessively rarified. While down below earth-level, of course, it would get more and more dense all the time, till at the bottom of a five-hundred-mile drop the density and pressure would be tremendous."

Beatrice made no answer. The spectacle she was gazing at filled her with solemn thoughts. Jagged, rent and riven, the rock extended downward. Here vast and broken ledges ran along its flanks--red, yellow, black, all seared and burned and vitrified as by the fire of h.e.l.l; there huge ma.s.ses, up-piled, seemed about to fall into the abyss.

A quarter-mile to southward, a rivulet had found its way over a projecting ledge. Spraying and silvery it fell, till, dissipated by the up-draft from the abyss, it dissolved in mist.

The ledge on which they were lying extended downward perhaps three hundred yards, then sloped backward, leaving sheer empty s.p.a.ce beneath them. They seemed to be poised in mid-heaven. It was totally unlike the sensation on a mountain-top, or even floating among the clouds; for a moment it seemed to Stern that he was looking up toward an unfathomable, infinite dome above him.

He shuddered, despite his cool and scientific spirit of observation.

"Some chemical action going on somewhere down there," said he, half to divert his own attention from his thoughts. "Smell that sulphur? If this place wasn't once the scene of volcanic activities, I'm no judge!"

A moderate yet very steady wind blew upward from the chasm, freighted with a scent of sulphur and some other substance new to Stern.

Beatrice, all at once overcome by sudden giddiness, drew back and hid her face in both hands.

"No bottom to it--no end!" she said in a scared tone. "Here's the end of the world, right here, and beyond this very rock--nothing!"

Stern, puzzled, shook his head.

"That's really impossible, absurd and ridiculous, of course," he answered. "There _must_ be something beyond. The way this stone falls proves that."

He pitched a two-pound lump of granite far out into the air. It fell vertically, whirling, and vanished with the speed of a meteor.

"If a whole side of the earth had split off, and what we see down below there were really sky, of course the earth's center of gravity would have shifted," he explained, "and that rock would have fallen in toward the cliff below us, not straight down."

"How can you be sure it doesn't fall that way after the impulse you gave it has been lost?"

"I shall have to make some close scientific tests here, lasting a day or two, before I'm positive; but my impression is that this, after all, is only a canyon--a split in the surface--rather than an actual end of the crust."

"But if it were a canyon, why should blue sky show down there at an angle of forty-five degrees?"

"I'll have to think that out, later," he replied. "Directly under us, you see all seems deep purple. That's another fact to consider. I tell you, Beatrice, there's more to be figured out here than can be done in half an hour.

"As I see it, some vast catastrophe must have rent the earth, a thousand or fifteen hundred years ago, as a result of which everybody was killed except you and me. We're standing now on the edge of the scar left by that explosion, or whatever it was. How deep or how wide that scar is, I don't know. Everything depends on our finding out, or at least on our guessing it with some degree of accuracy."

"How so?"

"Because, don't you see, this chasm stands between us and Chicago and the West, and all our hopes of finding human life there. And--"

"Why not coast south along the edge here, and see if we can't run across some ruined city or other where we can refill the tanks?"

"I'll think it over," the engineer answered. "In the meantime we can camp down here a couple of days or so, and rest; and I can make some calculations with a pendulum and so on."

"And if you decide there's probably another side to this gulf, what then?"

"We cross," he said; then for a while stood silent, musing as he peered down into the bottomless abyss that stretched there hungrily beneath their narrow observation-rock.

"We cross, that's all!"

CHAPTER XXI

LOST IN THE GREAT ABYSS

For two days they camped beside the chasm, resting, planning, discussing, while Stern, with improvised transits, pendulums and other apparatus, made tests and observations to determine, if possible, the properties of the great gap.

During this time they developed some theories regarding the catastrophe which had swept the world a thousand years ago.

"It seems highly and increasingly probable to me," the engineer said, after long thought, "that we have here the actual cause of the vast blight of death that left us two alone in the world. I rather think that at the time of the great explosion which produced this rent, certain highly poisonous gases were thrown off, to impregnate the entire atmosphere of the world. Everybody must have been killed at once. The poison must have swept the earth clean of human life."

"But how did _we_ escape?" asked the girl.

"That's hard telling. I figure it this way: The mephitic gas probably was heavy and dense, thus keeping to the lower air-strata, following them, over plain and hill and mountain, like a blanket of death.

"Just what happened to us, who can tell? Probably, tightly housed up there in the tower, the very highest inhabited spot in the world, only a very slight infiltration of the gas reached us. If my theory won't work, can you suggest a better one? Frankly, I can't; and until we have more facts, we've got to take what we have. No matter, the condition remains--we're alive and all the rest are dead; and I'm positive this cleft here is the cause of it."

"But if everybody's dead, as you say, why hunt for men?"

"Perhaps a handful may have survived among the highlands of the Rockies. I imagine that after the first great explosion there followed a series of terrible storms, tornadoes, volcanic eruptions, tidal waves and so on. You remember how I found the bones of a whale in lower Broadway; and many of the ruins in New York show the action of the sea--they're laid flat in such a manner as to indicate that the island was washed on one or two occasions by monster waves.

"Well, all these disturbances probably finished up what few survivors escaped, except possibly among the mountains of the West. A few scattered colonies may have survived a while--mining camps, for instance, or isolated prospectors, or what-not. They may all have died out, or again, they may have come together and reestablished some primitive form of barbarous or even savage life by this time. There's no telling. Our imperative problem is to reach that section and explore it thoroughly. For there, if anywhere, we'll find survivors of our race."

"How about that great maelstrom that nearly got us?" asked the girl."

Can you connect that with the catastrophe?"

"I think so. My idea is that, in some way or other, the sea is being sucked down into the interior of the earth and then hurled out again; maybe there's a gradual residue being left; maybe a great central lake or sea has formed. Who knows? At any rate all the drainage system of the country seems to have been changed and reversed in the most curious and unaccountable manner. I think we should find, if we could investigate everything thoroughly, that this vast chasm here is intimately connected with the whole thing."

These and many other questions perplexed the travelers, but most of all they sought to know the breadth of the vast gap and to determine if it had, as they hoped, another side, or if it were indeed the edge of an enormous ma.s.s split bodily off the earth.

Stern believed he had an answer to this problem on the afternoon of the second day. For many hours he had hung his pendulums over the cliff, noted deflections, taken triangulations, and covered the surface of the smooth stone with X's, Y's, Z's, sines and cosines and abstruse formulae--all scrawled with charcoal, his only means of writing.