"Night Land by William Hope Hodgson" (free download). Quote: "... a great circle of light, which was set up by the Earth-Current, and burned within a transparent tube; or had that appearance. And it bounded the Pyramid for a clear mile upon every side, and burned for ever; and none of the monsters had power to pass across, because of what we did call The Air Clog that it did make, as an invisible Wall of Safety"
The Project Gutenberg eBook of Rondah; or, thirty-three years in a star (free download/reading). Quote: "It was useless to try to find out where and of whom they had learned our language. They only could tell us that they had been taught from the Sun Island, a far-off land of the sea. Sometimes, they said, the tide was low and we could walk on dry rocks to the isle. Sometimes there was a “wall in the air.” Then no one could get there."
