The little bells of the brain are ringing in your ears; you hear nothing else—­not even a sigh of air—­not even the echo of a drop of water falling from the roof.  The guide triumphs in your look of amazement and awe; he falls to work on certain old wooden ruins, to you, yet invisible, and builds a brace or two of fires, by the aid of which you begin to have a better conception of the scene around you.  You are in the vestibule or ante-chamber, to which the spacious entrance of the Cave, and the narrow passage that succeeds it, should be considered the mere gate-way and covered approach.  It is a basilica of an oval figure—­two-hundred feet in length by one-hundred and fifty wide, with a roof which is as flat and level as if finished by the trowel of the plasterer, of fifty or sixty or even more feet in height.  Two passages, each a hundred feet in width, open into it at its opposite extremities, but at right angles to each other; and as they preserve a straight course for five or six-hundred feet, with the same flat roof common to each, the appearance to the eye, is that of a vast hall in the shape of the letter L expanded at the angle, both branches being five-hundred feet long by one-hundred wide.  The passage to the right hand is the “Great Bat Room;” (Audubon Avenue.) That in the front, the beginning of the Grand Gallery, or the Main Cavern itself.  The whole of this prodigious space is covered by a single rock, in which the eye can detect no break or interruption, save at its borders, where is a broad, sweeping cornice, traced in horizontal panel-work, exceedingly noble and regular; and not a single pier or pillar of any kind contributes to support it.  It needs no support.  It is like the arched and ponderous roof of the poet’s mausoleum: 

    “By its own weight made stedfast and immoveable.”

The floor is very irregularly broken, consisting of vast heaps of the nitrous earth, and of the ruins of the hoppers or vats, composed of heavy planking, in which the miners were accustomed to leach it.  The hall was, in fact, one of their chief factory rooms.  Before their day, it was a cemetery; and here they disinterred many a mouldering skeleton, belonging it seems, to that gigantic eight or nine feet race of men of past days, whose jaw-bones so many vivacious persons have clapped over their own, like horse-collars, without laying by a single one to convince the soul of scepticism.

Such is the vestibule of the Mammoth Cave,—­a hall which hundreds of visitors have passed through without being conscious of its existence.  The path, leading into the Grand Gallery, hugs the wall on the left hand; and is, besides, in a hollow, flanked on the right hand by lofty mounds of earth, which the visitor, if he looks at them at all, which he will scarcely do, at so early a period after entering, will readily suppose to be the opposite walls.  Those who enter the Great Bat Room, (Audubon Avenue,) into which flying visitors are seldom conducted, will indeed have some faint suspicion, for a moment, that they are passing through infinite space; but the walls of the Cave being so dark as to reflect not one single ray of light from the dim torches, and a greater number of them being necessary to disperse the gloom than are usually employed, they will still remain in ignorance of the grandeur around them.