Everything here is one surface: a shelf of ground that the tide washes over every four minutes. Wherever the ground dips and cannot drain as the tide falls, water stays behind, and that is a pool. There is one pool to begin with. Borers dig burrows and tunnels, masons fill hollows and raise walls, and breakers knock walls down, so the pools grow, join, drain, and form on their own. Pools are named as they appear. Artificers build structures in the water out of small parts, one at a time, each chosen from what is already around it: frames that bear load, solid plates, decks that reach out over the water, pods to live in, gears and tide wheels the tide turns, pipes, and lamps. Nothing is planned beyond the next part, so no two structures come out alike. A structure's footing is solid: the water goes around it, and the ground under it holds. Scrapers sleep in the pods, collectors keep hoards on the decks, and the tabs circle below and dart in among the frames when something startles them. Breakers work parts loose at the footing and artificers make them good again; when a footing gives way, everything it held falls. A tide wheel on a structure turns only while the water runs through it and stores its charge; the structure's lamps and windows burn at night only with a charged wheel nearby. Artificers also build working machines: a sluice gate on a pool's outlet shuts as the tide falls and holds the pool full, and a beacon, powered by a wheel, burns at night, feeds the plankton around it, and draws the tabs. Day turns to night every seven minutes, and the film on each floor grows only in wet light.
+Everything here is one surface: a shelf of ground that the tide washes over every four minutes. The tide's reach swells and shrinks over twenty minutes, so some low waters lay the shelf bare, and the rock stays dark where the water has just left it. Wherever the ground dips and cannot drain as the tide falls, water stays behind, and that is a pool. There is one pool to begin with. Borers dig burrows and tunnels, masons fill hollows and raise walls, and breakers knock walls down, so the pools grow, join, drain, and form on their own. Pools are named as they appear. Artificers build structures in the water out of small parts, one at a time, each chosen from what is already around it: frames that bear load, solid plates, decks that reach out over the water, pods to live in, gears and tide wheels the tide turns, pipes, and lamps. Nothing is planned beyond the next part, so no two structures come out alike. A structure's footing is solid: the water goes around it, and the ground under it holds. Scrapers sleep in the pods, collectors keep hoards on the decks, and the tabs circle below and dart in among the frames when something startles them. Breakers work parts loose at the footing and artificers make them good again; when a footing gives way, everything it held falls. A tide wheel on a structure turns only while the water runs through it and stores its charge; the structure's lamps and windows burn at night only with a charged wheel nearby. Artificers also build working machines: a sluice gate on a pool's outlet shuts as the tide falls and holds the pool full, and a beacon, powered by a wheel, burns at night, feeds the plankton around it, and draws the tabs. Now and then a storm comes in off the sea: the water rises and runs rough, the waves batter whatever stands at the waterline, and the fish hide among the frames. Day turns to night every seven minutes, and the film on each floor grows only in wet light. At night the plankton glows wherever something moves through it.