Proceeding onward about one-hundred feet, we reached a door, set in a rough stone wall, stretched across and completely blocking up the Cave; which was no sooner opened, than our lamps were extinguished by the violence of the wind rushing outwards. An accurate estimate of the external temperature, may at any time, be made, by noting the force of the wind as it blows inward or outward. When it is very warm without, the wind blows outwards with violence; but when cold, it blows inwards with proportionate force. The temperature of the Cave, (winter and summer,) is invariably the same--59 deg. Fahrenheit; and its atmosphere is perfectly uniform, dry, and of most extraordinary salubrity. Our lamps being relighted, we soon reached a narrow passage faced on the left side by a wall, built by the miners to confine the loose stone thrown up in the course of their operations, when gradually descending a short distance, we entered the great vestibule or ante-chamber of the Cave. What do we now see? Midnight!--the blackness of darkness!--Nothing! Where is the wall we were lately elbowing out of the way? It has vanished!--It is lost! We are walled in by darkness, and darkness canopies us above. Look again;--Swing your torches aloft! Aye, now you can see it; far up, a hundred feet above your head, a grey ceiling rolling dimly away like a cloud, and heavy buttresses, bending under the weight, curling and toppling over their base, begin to project their enormous masses from the shadowy wall. How vast! How solemn! How awful! 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