Cloud belt

The cloud bank was a layer of crystalline fog in the atmosphere above Sardicktown. Sky fish were able to swim through the electricity in the fog. Elliot and Kazran Sardick built a machine to control its opacity, allowing the fish to pass through at their will. One day the bank fell and a shoal of sky fish attacked a school. No one was seriously hurt. Human singing resonated the crystals in the fog and created delta waves, which attracted the fish. (TV: A Christmas Carol)