The walls closed in again, and the river and the path resumed. This time he saw shapes in the water: eyeless, rubbery fins, flexing about from side to side along the bottom. Marine life, at last.

The miles passed uneventfully. Abruptly the passage ended. The water plunged from a tall vertical tunnel, bubbling in a circular pool and flowing on into the bed he had been tracing. The path circled this small pool and diverged. Through the rock it bored, a round passage.

Aton looked down that sharply cut passage and saw nothing. He put his ear to the wall and heard a distant tapping, a heartbeat. Something was at the other end. Something large.

He looked into the pool and saw a strange globular jellyfish deep below, perhaps a yard in diameter, balanced in a pothole just out of the striking falls. He craned upward and saw—light. Daylight.

The wall of the shaft was rough. The severed strata defended themselves in concentric circles, some reaching an inch or more in toward the glassy column of plummeting water. One side was comparatively smooth, as though the water had eroded it clean during some capricious housekeeping effort; but now there was a foot or more of space on every side, between wall and water.

Aton removed his water-skin—a ludicrous impediment in the circumstances—parked it with his other supplies, and prepared for the most difficult climb of his life.

The diameter of the shaft was about a yard at the bottom, and it appeared to expand slightly at the top. Aton braced his back against the smooth side, spread his arms in a semicircle against the wall at shoulder level, and lifted one foot around the devastating center column to find a purchase against the opposite side. He brought the other foot into play and began to climb, letting the river plunge harmlessly between his spread thighs. With his arms he lifted his back away and up; then took two baby steps up the far side. Again and again, advancing two to three inches at a time.

The climb was not hard, at first, but there was a long way to go.

He decided not to conserve his strength, since even the act of resting in such a position would fatigue him. If he could achieve the top quickly, there should be ample opportunity to rest. If he did not get there promptly, fatigue might prevent him from reaching it at all.

He accelerated his pace, humping up in a rocking pattern, sometimes, painfully, the muscles of his legs bunching and relaxing and bunching again. His arms grew tired first, and he turned them down at the elbows, wriggling just enough to make progress, scraping his elbows but not caring.