I have referred only to the surface, the skin formation of this honeycombed labyrinth, the entrance to the future wonderland of the world. Portions of such a superficial cavern maze have been traversed by man in the ramifications known as the Mammoth Cave, but deeper than man has yet explored, the subcutaneous structure of that series of caverns is yet to be investigated. The Mammoth Cave as now traversed is simply a superficial series of grottoes and passages overlying the deeper cavern field that I have described. The explored chain of passages is of great interest to men, it is true, but of minor importance compared to others yet unknown, being in fact, the result of mere surface erosion. The river that bisects the cave, just beneath the surface of the earth, and known as Echo River, is a miniature stream: there are others more magnificent that flow majestically far, far beneath it. As we descend into the earth in that locality, caverns multiply in number and increase in size, retaining the general configuration of those I have described. The layers of rock are thicker, the intervening spaces broader; and the spaces stretch in increasingly expanded chambers for miles, while high above each series of caverns the solid ceilings of stone arch and interarch. Sheltered under these subterrene alcoves are streams, lakes, rivers and water-falls. Near the surface of the earth such waters often teem with aquatic life, and some of the caves are inhabited by species of birds, reptiles and mammals as yet unknown to men, creatures possessed of senses and organs that are different from any we find with surface animals, and also apparently defective in particulars that would startle persons acquainted only with creatures that live in the sunshine. It is a world beneath a world, a world within a world--" My guide abruptly stopped. I sat entranced, marveling at the young-old adept's knowledge, admiring his accomplishments. I gazed into the cavity that yawned beneath me, and imagined its possible but to me invisible secrets, enraptured with the thought of searching into them. Who would not feel elated at the prospect of an exploration, such as I foresaw might be pursued in my immediate future? I had often been charmed with narrative descriptions of discoveries, and book accounts of scientific investigations, but I had never pictured myself as a participant in such fascinating enterprises. "Indeed, indeed," I cried exultingly; "lead me to this Wonderland, show me the entrance to this Subterranean World, and I promise willingly to do as you bid."