Black Diamonds A Novel

We are in the depths of an underground cavern. It is bad enough to be underground, but here we are all enveloped in black as well: the ceiling is black, so are the walls; they are made of blocks of coal. The floor is one great black looking-glass. It is a sort of pond, polished as steel. Over this polished surface glistens the reflection of a solitary light, the light of a safety-lamp shining through a wire net. A man guides himself over the pond in a narrow boat. By the doubtful light of the lamp he sees high pillars, which rise out of the depths below and reach to the very roof of the cavern-pillars slender, like the columns of a Moorish palace. These pillars are half white and half black; up to a certain point only are they coal black, beyond that they are light in color. What are these pillars?