by Greg Egan
Seth was about to volunteer to help her with the descent when she asked for him specifically. He put on a harness, gathered the tools she’d requested into a spare pack, picked up his stilt, attached the wedge to his right foot, then squeezed past Andrei and Sarah and stepped out onto the slope.
The moment his stilt made contact with the rock he could feel the small pits and bumps in the surface, which rendered it far less slippery than the practice ramp. Seth was sure that in the long run this rougher texture would make things easier, but he was also aware that some of the hard-won instincts he’d acquired in training were now obsolete. After clipping his harness to the northern safety rope he spent a few moments recalibrating his sense of the forces at play, and adjusting his posture accordingly. Then he set off across the rock.
Out on the slope, Theo’s southern blind spot was far more unsettling than it had been from the roof of the basket. At first, Seth took some comfort from the fact that if he went sliding at least it would be upslope, allowing him to see where he was going—but then he realized that that wasn’t necessarily true. The basket’s immediate surroundings were certainly tilted at just below forty-five degrees, but any shift to a slightly greater angle might be impossible to discern until the moment he felt the unexpected force on the stilt that sent him toppling. The safety harness should have reassured him that he wasn’t going to fall in any direction, but the eerie, asymmetric emptiness to the south imbued everything with a sense of imbalance.
«You know what would be worse than skidding blindly down the slope and crashing onto the terrace?» he asked Theo.
«Skidding blindly down the slope and overshooting the terrace, so we keep on falling.»
But once Seth was able to see the terrace clearly, his anxiety began to diminish. His mind seized on the stretch of level ground ahead and extrapolated its presence backward, not exactly filling the blind spot, but robbing it of much of its potency.
When he arrived at the cliff’s edge, he called to Sarah to dispense some more rope from the southern spool, but he held it back from Raina and let it hang slackly between them. He took a wedge-mounted pulley out of his pack, coiled some of the rope around the pulley, handed it to Raina, then stepped back to get a better view.
Even with her stilt raising one leg above the ground, Raina could reach all the way down to the edge by swinging her arm out to the south, but it was not an ideal posture to see what she was doing, so she needed Seth’s perspective to guide her. By adjusting the vertical plate that protruded from the southern face of the pulley’s mount and hung over the drop, she was able to counterbalance the tendency of the mount to slide north, at least to the point where it was stable against small disturbances.
“Now comes the fun part,” Raina muttered. She summoned Seth forward and rested an arm on his shoulder so she could keep her balance while she released her stilt’s locking pins, collapsed it and put it in her pack. She unclipped the northern safety rope, and passed the end to him so he could secure it to his own harness.
Then she jumped sideways over the cliff.
Seth heard a solid thwack of flesh against rock as the rope threading through the pulley went taut. “Are you all right?” he asked.
Raina grunted irritably, but Amina replied, “Yes!”
Seth kept a close watch on the pulley and conveyed instructions from below back to Sarah, until Raina announced, “We’re down.”
A short time later she came into view, walking slowly west along the terrace. “It looks like the same kind of rock as the rest of the slope,” Amina said. “Maybe there was some pre-existing fissure or inhomogeneity here, but it’s not an entirely different mineral.”
Raina walked up to the nearest of the boulders and squatted down to inspect its base. “It’s not contiguous,” she declared. Seth was surprised that there wasn’t more rubble on the terraces, since they seemed to be the only places anything could rest, but perhaps over time the wind had removed most of the smaller rocks, sending them sliding from terrace to terrace until they’d been ground into dust.
Eventually Raina was satisfied. “We’ll be safer here, and we’ll be able to travel faster. We should start bringing everyone down.”
as the expedition began the long march west, Seth looked back to commit to memory the view from a distance of the part of the terrace near the rope they’d left dangling over the small cliff. If they lost this slender thread they might still find their way back to the basket, but if they could not locate the basket itself they’d almost certainly perish. Seth had never faced a situation before when a failure to retrace his steps could extract such an unforgiving penalty.
The terrace was more than wide enough for all four Walkers to stay abreast of each other, but after a while they settled into a staggered formation. With Sarah and Judith to the south of him, interrupting the void, and the vertical cliff face to the north replacing the foggy presence of the slope, Seth felt as if something close to normality had been restored.
«Do you think we should change places every now and then?» he asked Theo.
«Why?»
«To give Judith something to ping to the south. If my left eye received no light at all for a couple of days, I wouldn’t want to rely on it working normally the instant I had need of it. Aren’t your pingers the same?»
«I never thought about it,» Theo admitted. «But I have no problem taking an equal share of the sensory deprivation.»
To measure their progress they used callipers to position themselves at a known distance from a prominent feature on the cliffs, which they sighted through an alidade to record its inclination and calculate its height. By repeating the sighting some time later they could determine how far they’d come, before switching to a new point of reference. The cumulative errors in these measurements would mount up as they traveled, but the conventional methods of estimating latitude and longitude simply weren’t available.
Even in this land without shadows, though, a rough sense of the motion of the sun could be obtained from the shifting pattern of intensity in the haze of scattered light from above. Midday arrived sooner than Seth had been expecting it; what had passed for dawn must have been later than he’d realized in the already short summer day up on the surface. But it was cooler than it had been in the steamlands at midnight, and when they stopped to eat he had no trouble rationing his water.
While the rest of the team sat digesting their meals, Ada took the opportunity to scrutinize the cliff face, sidling up close and then walking back and forth beside it, jotting occasional notes into a book she was carrying.
“So how can you be sure what the textures of the rock are?” Seth asked her. Ordinary Walkers and Siders trusted the perceptions they shared because they’d known each other since birth—but what credence should anyone give to the visions of a drug-addled slave?
“The same way as you,” Ada replied cheerfully. “I see the rock too, I touch it too. If it’s all consistent, why wouldn’t I trust the details that each modality reveals?”
Each modality? Seth wasn’t sure what kind of response he’d expected, but the sheer brazenness of this answer was shocking. To her, a Sider was just one more sensory organ.
Ada continued her examination of the cliff face, showing no signs of discomfort at his question. Seth’s anger began to dissipate under the weight of its own uselessness. If he started treating every ordinary thing she did as a provocation, he’d poison the whole expedition with his rancor. He did not want to spend the next hundred days ineffectually venting his outrage while he vacillated between the position that Ada, having had no choice in her upbringing, deserved only pity, and the undeniable fact that her Sider had suffered an incomparably worse fate.
«Good luck with that “runaway fault ejection” hypothesis,» Theo scoffed. «She’ll need a trail of matching rubble from here to the midwinter circle to account for all the excavated rock.»
Seth didn’t reply. He could hardly blame Theo for his own ineffectual venting . . . but all their gestu
res of contempt would do nothing to resolve the plight of Thanton’s Siders. In the end they’d both have to find a way to get along with this particular Thantonite—and promise themselves that they’d engage with the cause in a far more useful fashion once the mission was over.
seth was woken by a gentle rain falling on the terrace. He left his tent and set up a funnel to replenish the canteens, working by touch in the darkness.
«All the spillage is away from us,» Theo observed. The terrace itself sloped down a little to the south, and some water was pooling on the north side beneath the cliffs—but none was spraying up over the southern edge, or drizzling down from the top of the cliffs.
«We must be on a transition line,» Seth concluded. The slope to the south of them had to be slightly steeper than forty-five degrees, and that to the north a little less steep. «Maybe that’s the most likely place for terraces to form, because there’s some kind of extra strain in the rock.»
He left the canteens to fill and stood beside the tent in a sheltered spot, brushing some of the water off himself before re-entering.
“Is the rain going to be a problem?” Andrei asked.
Theo described the situation.
“So when this terrace comes to an end, the best way to find the next one might be to follow the transition line,” Nicholas suggested.
“Follow it how?” Seth wondered. “Unless it’s raining, the cues could be almost imperceptible.”
“If you start out with one foot on either side of the line,” Andrei proposed, “it would be easy to tell the difference if you ever stopped straddling it.”
Seth suspected that this might be an understatement. “So to get around the visibility problem, we arrange to be sent sprawling if we take one wrong step?”
Andrei laughed. “Not if we’re prepared! And we’re much less likely to be taken by surprise by any meandering of the line if it starts out right between our feet, than if all we know is that it was once so many paces to the north or south.”
“How did the surface end up so close to forty-five degrees?” Nicholas mused. “I don’t believe it was a fault ejection, it’s too large for that. But if it was extrusion from the pressure in the rock, why should it stop at precisely that angle?”
Theo said, “Maybe it hasn’t stopped—but weathering keeps the angle close to forty-five degrees. If you have part of a stream running as fast as possible, and it hits a section of the slope with a different gradient that impedes the flow, over time isn’t that obstacle going to be carved away?”
Nicholas considered this. “But how much water would there have been here in the past, when the steamlands were still far to the north?”
“That’s hard to say,” Theo admitted. “When it was absolute summer up on the surface . . . what was the weather like down here?”
Andrei said, “You still believe this is the edge of the world?” His tone was challenging but not derisive; he wasn’t simply ridiculing the hypothesis.
“Yes,” Theo replied.
“Then if you want to understand the long-term hydrology of this place, shouldn’t you be asking yourself about the weather much, much further down?”
late in the morning of their eighth day on the slope, the terrace came to an end.
They had seen the cliff face slowly shrinking beside them for days, and the edge of the southern drop drawing nearer, but Seth had kept telling himself that the trend was as likely to reverse as to continue. Then the point where the ledge finally shrank out of existence came into view to the west, and they’d been left marching toward its demise, unable to stop grumbling about an event they’d always known was inevitable.
“I’m just glad that all those days we spent practicing on the ramp weren’t for nothing,” Sarah declared sarcastically. Seth tried not to think about how arduous he’d found the short journey from the basket to the terrace, even with the safety ropes to give him confidence and the reward of level ground in sight. If there was another terrace farther west on the same transition line, it was not yet visible. All he could see ahead was a roughly planar expanse of brown rock at the slope’s usual incline, dotted with outcrops that looked more like obstacles than potential resting points.
The final section of the ledge was narrow enough to force them to move in single file. Andrei and Nicholas were at the front, followed by Raina and Amina, Sarah and Judith, Seth and Theo, and Ada in the rear. They shuffled forward cautiously, well separated so there’d be no chance of bumping one another.
Andrei called a halt and began preparing himself. Seth couldn’t see what he was doing, but he could hear a stilt being expanded and the locking pins snapping into place. There was a steady wind blowing from the south; a day earlier, he would have enjoyed its touch on his skin, but now it just felt like a threat to his balance. He glanced down at the emergency hooks strapped to his wrists; the spikes were intended to offer some hope of getting purchase on the rock if he went sliding, sparing him the likely flaying if he tried to achieve the same result with his bare hands. Without shifting his feet on the ledge, he stretched an arm out and pressed one hook against the slope to the north. The tip lodged in a small depression in the rock, but it took no effort at all to scrape it across the surface.
Ada said, “It might still slow you down, even if it can’t bring you to a halt immediately.”
“That’s true,” Seth replied.
“Here we go,” Andrei announced.
Seth heard the tap of stilt on rock, and the softer step of the leveling wedge. Andrei muttered something incoherent, then there was a second tap, a second step completed.
Five footfalls later, a pause. “It’s not too bad,” Andrei decided. “You just need to lean inward from whichever foot you’re keeping on the ground. And standing motionless feels easier than it did near the basket: you just need to tense your upper legs a bit.”
With that, he set off again. Raina and Amina followed him, swiftly, without commentary. Seth took his stilt from his pack and readied it for use.
Sarah shuffled forward and used her stilt to stay balanced while she lifted her right foot to attach the leveling wedge. Seth could see the point a pace in front of her where what remained of the terrace finally crumbled away to nothing. A morbid image came to him, unbidden: Amir and Aziz comforting their children, while Seth looked on helplessly. The only way he could banish it was with an equally lurid fantasy: if Sarah and Judith were taken by the slope, he’d throw himself after them in a doomed attempt at a rescue. In the irrational logic of his competing anxieties, the absurd grandiosity of this imaginary gesture made the imaginary antecedent seem far less likely.
Sarah stepped out onto the slope and began to walk, swaying inward with each step as Andrei had counseled. She made it look easy.
Seth fitted his wedge and replayed Sarah’s successful transition in his mind, then he mimicked her as closely as he could, making contact with the slope in all the same places. When the memory guiding this impersonation came to an end, he hesitated, unnerved for a moment, but then he reached back to the rhythms of the steps he’d just taken, recalled the sensations in his joints and muscles, and resumed the act of mimicry in the first person.
After a dozen steps, he looked back to check on Ada. She was off the ledge, following him, a little shaky but not in trouble. “You’re doing well,” he said.
“You too,” she replied.
He tipped his head back to the west. Whatever he felt about Ada’s culpability, to deny anyone in this situation a few moments of reassurance and solidarity would be barbaric.
The practice ramp hadn’t included anything quite like the transition line they were straddling, but to Seth the habit of giving his full attention to the placement of wedge and stilt, over and over, seemed invaluable regardless of the details of the surface. He lost himself in the minutiae of the act, the judgments of balance, forces, and friction.
Andrei called back, “It veers south a little, from where I am now!” Seth searched for some distinguishing feature
on the visible part of the slope that would help him identify the spot; he settled on a small outcrop to the north of Andrei’s current position, and described the choice to Theo.
«Will you recognize that when you’re pinging it?» Seth wasn’t confident that he’d be able to make the connection himself; he hadn’t been paying much attention to Theo’s view since moving off the ledge, but after days with the vertical cliff face to his north, the one thing he knew was that he was still at risk of misreading the slope’s strange echoes.
«I’ll keep track of it as it crosses the cone,» Theo assured him.
«Tell me if my gaze drops too low.»
«Don’t worry about that. Just concentrate on walking safely.»
«All right.»
As he approached the bend in the transition line, Seth wondered about Ada. With no one to share the task with her, would it be a struggle to coordinate the information, or was she so accustomed to doing everything for herself that this would be no different? If Walkers had been born with pingers sprouting from their skulls, they might have learned to make sense of every echo, unaided. So perhaps that was how she thought of herself: a Walker who could see north and south, more entitled to claim those sensory organs as her own than the sleeping Sider who had never really used them.
Theo said, «Your landmark’s coming up to due north of us right now.»
«Thanks.» Seth shifted his gait toward the south, stepping slowly to be sure that he hadn’t left the turn too late. As he brought his northern, wedged foot tentatively down, he felt the slope sending him an unexpected signal: it wanted him to slide down, to the south. He’d made the turn too early, not too late.
He calmed himself, and adjusted his posture, shifting his weight to retain his balance. He took another step, directly west, with the stilt and then the wedge again. This time, the wedge landed north of the transition line.
«This isn’t going to be easy,» he admitted.