Ann hiked along much more comfortably than she had in Hippolyta, with the unconscious grace of someone who has spent a lot of time walking on rock. Boulder ballet; she carried a long angular hammer in her thick glove, and her thigh pockets bulged with specimens. She didn’t respond to the exclamations of Zo or the guardian group, she was oblivious to them. Like an actor playing the part of Ann Clayborne. Zo laughed: that one could become such a cliché!

“If they domed this dark backward and abysm of time, it would make a beautiful place to live,” she said. “Lots of land for the amount of tent needed, eh? And such a view. It would be a wonder.”

No response to such a blunt provocation, of course. But it would set them thinking. Zo followed the guardian group like an albatross. They had started descending a broken staircase of rock that lined the edge of a slim buttress, extending far out from the chasm wall, like a fold of drapery in a marble statue. This feature ended in a flat swirl several kilometers out from the wall, and a kilometer or more lower than the rim. After the flat spot the buttress fell away abruptly, in a sheer drop to the chasm floor, some twenty kilometers straight down. Twenty kilometers! Twenty thousand meters, some seventy thousand feet. . . . Even great Mars itself could boast no such wall.

There were a number of buttresses and other deformations on the wall similar to the one they were hiking out on: flutings and draperies, as in a limestone cavern, but formed all at once; the wall had been melted, molten rock had dripped into the abyss until the chill of space had frozen it forever. Everything was visible from every point of their descent. A railing had been bolted to the buttress’s edge, and they were all clipped to this railing by lines, connected to harnesses in their spacesuits; a good thing, as the edge of the buttress was narrow, and the slightest slip sideways could launch one out into the space of the chasm. The spidery little spacecraft that had dropped them off was going to fly down and take them off at the bottom of the staircase, from the flat spot at the end of the buttress promontory. So they could descend without a worry for the return; and descend they did, for minute after minute, in a silence that was not at all companionable. Zo had to grin; you could almost hear them thinking black thoughts at her, the grinding was palpable. Except for Ann, who was stopping every few meters to inspect the cracks between their rough stairs.