I call it wondrous because of it we could see neither the beginning nor the end, nor the roof, nor aught else save the rock on which we walked, and the side or wall that our hands touched.

Nor was this because of darkness, since although it was not illuminated like the upper caverns, light of a sort was present.
It was a very strange light, consisting of brilliant and intermittent flashes, or globes of blue and lambent flame which seemed to leap from nowhere into nowhere, or sometimes to hang poised in mid air.
"How odd they are," said the voice of Bastin behind me.

"They remind me of those blue sparks which jump up from the wires of the tramways in London on a dark night.

You know, don't you, Bickley?
I mean when the conductor pulls round that long stick with an iron wheel on the top of it." "Nobody but you could have thought of such a comparison, Bastin," answered Bickley.

"Still, multiplied a thousandfold they are not unlike." Nor indeed were they, except that each blue flash was as big as the full moon and in one place or another they were so continuous that one could have read a letter by their light.