_Mammoth Cave_ is situated near the Green river in Kentucky, the entrance to which is by a pit forty feet deep, and one hundred and twenty in circumference. At the bottom of this pit is the mouth of the cave, which is open to the north, and is from forty to fifty feet in height, and thirty in width, for upwards of forty rods, when it becomes not more than ten feet wide and five feet high. ‘However,’ says Dr. Wood, ‘this continues but a short distance, when it expands to thirty or forty feet in width, and is about twenty feet in height, for about one mile, until you come to the first _hopper_, where salt-petre is manufactured. Thence it is about forty feet in width, and eighty in height, till you arrive at the second hopper two miles from the mouth. The loose limestone has been laid up into handsome walls on either side, almost the whole distance from the entrance to the second hopper. The road is hard, and as smooth as a flag pavement. The walls of the cavern are perpendicular in every passage that I traversed; the arches are regular in every part, and have bid defiance even to earthquakes. As you advance into the cave, the avenue leads from the second hopper west one mile, then south-west to the chief city, which is six miles distant from the entrance. This avenue is from sixty to one hundred feet high, and about the same broad, the whole distance from the second hopper, until you come to the cross-roads or chief city; and is nearly upon a level, the floor or bottom being covered with loose limestone and salt-petre earth. When I reached the immense area, (chief city,) containing upward of eight acres, without a single pillar to support the arch, which is entire over the whole, I was struck dumb with astonishment, and can give but a very faint idea of its splendor. Nothing under heaven can be more sublime and grand than this place, covered with one solid arch, at least one hundred feet in height, and to all appearance entire. After entering the chief city, I perceived five avenues leading out of it from sixty to one hundred feet in width, and from forty to eighty in height. The walls (all of stone) are arched, being from forty to eighty feet of perpendicular height, before the arch commences.