In many places the mile-high walls were without a single ledge to break their vertical faces. When they came to the first such place they saw that the ground near the base was riddled with queer little pits, like tiny craters of the moon. As they looked there was a crack like a cannon shot and the ground beside them erupted into an explosion of sand and gravel. When the dust had cleared away there was a new crater where none had been before.

Humbolt wiped the blood from his face where a flying fragment had cut it and said, “The heat of the sun loosens rocks up on the rim. When one falls a mile in a one point five gravity, it’s traveling like a meteor.”

They went on, through the danger zone. As with the peril of the chasm’s heat, there was no choice. Only by observing the material that littered the base of the cliffs could they know what minerals, if any, might be above them.

On the fifteenth day they saw the red-stained stratum. Humbolt quickened his pace, hurrying forward in advance of Barber. The stratum was too high up on the wall to be reached but it was not necessary to examine it in place⁠—the base of the cliff was piled thick with fragments from it.

He felt the first touch of discouragement as he looked at them. They were a sandstone, light in weight. The iron present was only what the Dunbar Expedition had thought it to be; a mere discoloration.

They made their way slowly along the foot of the cliff, examining piece after piece in the hope of finding something more than iron stains. There was no variation, however, and a mile farther on they came to the end of the red stratum. Beyond that point the rocks were gray, without a vestige of iron.

“So that,” Barber said, looking back the way they had come, “is what we were going to build a ship out of⁠—iron stains!”