"True," he answered, "as you measure distance on the surface of the earth, and you could not walk it in years of time; but you are now twenty-five miles below the surface, and you must be aware that instead of becoming more weary as we proceed, you are now and have for some time been gaining strength. I would also call to your attention that you neither hunger nor thirst." "Proceed," I said, "'tis useless to rebel; I am wholly in your power," and we resumed our journey, and rapidly went forward amid silences that were to me painful beyond description. We abruptly entered a cavern of crystal, every portion of which was of sparkling brilliancy, and as white as snow. The stalactites, stalagmites and fungi disappeared. I picked up a fragment of the bright material, tasted it, and found that it resembled pure salt. Monstrous, cubical crystals, a foot or more in diameter, stood out in bold relief, accumulations of them, as conglomerated masses, banked up here and there, making parts of great columnar cliffs, while in other formations the crystals were small, resembling in the aggregate masses of white sandstone. "Is not this salt?" I asked. "Yes; we are now in the dried bed of an underground lake." "Dried bed?" I exclaimed; "a body of water sealed in the earth can not evaporate." "It has not evaporated; at some remote period the water has been abstracted from the salt, and probably has escaped upon the surface of the earth as a fresh water spring." "You contradict all laws of hydrostatics, as I understand that subject," I replied, "when you speak of abstracting water from a dissolved substance that is part of a liquid, and thus leaving the solids." "Nevertheless this is a constant act of nature," said he; "how else can you rationally account for the great salt beds and other deposits of saline materials that exist hermetically sealed beneath the earth's surface?" [Illustration: "MONSTROUS CUBICAL CRYSTALS."] "I will confess that I have not given the subject much thought; I simply accept the usual explanation to the effect that salty seas have lost their water by evaporation, and afterward the salt formations, by some convulsions of nature, have been covered with earth, perhaps sinking by earthquake convulsions bodily into the earth." "These explanations are examples of some of the erroneous views of scientific writers," he replied; "they are true only to a limited extent. The great beds of salt, deep in the earth, are usually accumulations left there by water that is drawn from brine lakes, from which the liberated water often escaped as pure spring water at the surface of the earth. It does not escape by evaporation, at least not until it reaches the earth's surface." INTERLUDE--THE STORY INTERRUPTED. CHAPTER XX. MY UNBIDDEN GUEST PROVES HIS STATEMENT AND REFUTES MY PHILOSOPHY.