At the base of the four-thousand-ton rock plug, beneath the protective canopy of the four heart-oak baulks, lay the ancient pilot water chute. It was a narrow natural opening, barely eighteen inches wide and three feet high. There, the underground river had flowed for ten thousand years before the Dragon-Slayers choked the throat with their dynamite.
Now, that water chute was plugged by a single key stone. A three-ton wedge of crystal-clear chert, jammed tight like a bung in a beer cask.
Tomas Reed knelt in four inches of freezing water at the mouth of the water chute, his animal fat lamp shielded by his knee. In his right hand he held an ash-wood packing rod. Between his knees sat a small zinc canister containing exactly four ounces of steadied nitro-glycerine paste, taken from the oat-flour crusts of the disarmed kegs.
Before striking the match, Tomas knelt by the zinc canister to inspect the fuse casing. A damp slow-match was the sapper’s curse. If the flame sputtered out four inches inside the tamping clay, a man had to crawl into the hole to dig out twenty grains of live fulminate with a wooden spoon. A task that had cost thirty apprentices their eyes in the siege trenches of the Northern Marches.
