Lake examined the sheets of mica. “We could make windows for the outer caves of these,” he said. “Have them double thickness with a wide air space between, for insulation. As for the quartz crystals.⁠ ⁠…”

“Optical instruments,” Craig said. “Binoculars, microscopes⁠—it would take us a long time to learn how to make glass as clear and flawless as those crystals. But we have no way of cutting and grinding them.”

Craig went to the east that fall and to the west the next spring. He returned from the trip to the west with a twisted knee that would never let him go prospecting again.

“It will take years to find the metals we need,” he said. “The indications are that we never will but I wanted to keep on trying. Now, my damned knee has me chained to these caves.⁠ ⁠…”

He reconciled himself to his lameness and confinement as best he could and finished his textbook: Geology and Mineral Identification .