At the four-hundred-pace landing, the upright reference shaft opened into a huge, circular spreading chamber twelve paces across. The ceiling arched overhead in a self-supporting dome of dark, swirling migmatite, supported by four huge pillars of living rock left intact by the ancient survey corps. In the center of the floor stood a raised circular instrument stone stand carved with the survey corps’ eight-pointed compass rose and four sunken brass posture sockets.
Streaming outward from the central chamber at the cardinal compass points were four level check tunnels—the intermediate grid drifts. Each drift was cut six feet high and four feet wide. He extended exactly two hundred and fifty-six paces outward to the quarter-width marks of the thousand-pace prism.
Kezra set her pack on an ancient stone surveying bench carved into the western pillar. She unrolled her linen plan of the 400-pace level, weighting the edges with two brass line-weight bobs.
“Here is our task for this afternoon, Voss,” Kezra said, tracing the four outward lines with her quill. “The 400-pace intermediate grid. We have to walk all four outward drifts: North, South, East, and West. At every thirty-two-pace station, we set the rod into the floor socket, strike three sounding triplets, and record the level rebound matrix. That confirms that the rock mass between the central shaft and the outer boundary is nonstop and free of water-filled caverns or void pockets.”
