Beyond the Grand Cross-hall and the High Meridian Prow, between Entry halls 098 and 104, the dark waters of the Ark came together into the Great Circulatory Canal.
This was not a stale pool or a dead moat. It was the main blood drain tube of the three-mile-long vessel—a vaulted underground river twelve paces wide and six deep-water lengths deep, carved directly through the living dark rock keel. In ancient times, this channel had circulated distilled seawater through fourteen point eight miles of lower cooling jackets. It drained away the huge earth-heat generated by the deep magma chimneys beneath the ocean floor.
The stonework of this great chimney pipe had been cut from dark, fine-grained gabbro, dressed by ancient stonemasons to an accuracy of a tiny fraction of an inch. Every forty paces, transverse arch-ribs of dense white hard speckled rock heavy the ceiling, designed to resist the crushing weight of eighty thousand deep-water lengths of overlying ocean. Along the underwater haunches of the walls ran triple lines of bronze cry-holes, fitted with one-way leather flapper valves that allowed internal groundwater to drain into the canal while preventing high-pressure deep-sea seawater from blowing back into the inside galleries.
For two thousand years, this underground river had flowed in total, pitch-black silence, witnessed only by blind crabs and deep-sea stone polyps clinging to the stonework.
