The sound that followed the collapse of the dome was not the rumble of settling stone.
It was a breath out of terrifying size. A deep, underground groan that rose from forty arm-lengths beneath the floor flags as the eight-foot arch of linked hard speckled rock that spanned the Vertical Deep gap began to split apart.
The floor of the Grand Round hall had never been solid bedrock. For twelve thousand years, the two-hundred-arm-length circle of polished hard speckled rock had rested as a huge, inverted saucer suspended over an infinite underground deep pit, held in static balance by the outward crushing thrust of its outer edge abutments. But the dynamic moving impact of two thousand four hundred and eighty metric tons of falling dark rock—striking the center of the hall from a height of eighty arm-lengths—had exceeded the ultimate shear limit of the stonework by three hundred percent.
Across the circular floor, streaming outward from the forty-foot mountain of crushed rubble in the center like the spokes of a huge black wheel, ran twenty-four jagged, widening chasms.
The cracks were not hairline fissures. They were gaping rifts two arm-lengths wide, splitting through five feet of polished hard speckled rock flags and three feet of load-bearing greenstone beneath. From the black depths of those rifts rose a blast of freezing, high-pressure air that smelled of ancient hadal depths. The cold, stone scent of drowned continents, crushed sea-sponge, and stone-hard kelp that had rested in darkness for sixty thousand tides.
