Far below them was a plateau, stretching endlessly like the one they had left behind them. But the chasm dominated all else. It was a gigantic, sheer-walled valley, a hundred miles long by forty miles wide, sunk deep in the plateau with the tops of its mile-high walls level with the floor of the plateau. The mountain under them dropped swiftly away, sloping down and down to the level of the plateau and then on, down and down again, to the bottom of the chasm that was so deep its floor was half hidden by the morning shadows.

“My God!” Barber said. “It must be over three miles under us to the bottom, on the vertical. Ten miles of thirty-three percent grade⁠—if we go down we’ll never get out again.”

“You can turn back here if you want to,” Humbolt said.

“Turn back?” Barber’s red whiskers seemed to bristle. “Who in hell said anything about turning back?”

“Nobody,” Humbolt said, smiling a little at Barber’s quick flash of anger.