MAMMOTH CAVE, the largest cavern known, situated in Edmondson co., near Green river, in Kentucky, about 75 m. S. S. W. of Louisville. Its mouth is reached by passing down a wild rocky ravine through a dense forest; it is an irregular, funnel-shaped opening, from 50 to 100 ft. in diameter at the top, with steep walls about 50 ft. high. The cave extends about nine miles, and it is said that to visit the portions already traversed requires from 150 to 200 miles of travel. This vast interior contains a succession of marvellous avenues, chambers, domes, abysses, grottoes, lakes, rivers, cataracts, &c., which for size and wonderful appearance are unsurpassed. The rocks present numerous forms and shapes of objects in the external world, while stalagmites and stalactites of gigantic size and fantastic form abound, though not so brilliant and beautiful as are found in some other caves. Chief among the objects of interest are Silliman's avenue, about 1½ m. long, from 20 to 200 ft. wide, and from 20 to 40 ft. high; Marion's avenue, of about the same dimensions; the Star chamber, about 500 ft. long and 70 ft. wide, the ceiling of which, 70 ft. high, is composed of black gypsum, and is studded with innumerable white points, which by a dim light present a most striking resemblance to stars; and Cleveland's cabinet, an avenue about 2 m. long, spanned by an arch of 50 ft, with an average central height of 10 ft. By many the last is regarded as the most wonderful object in the cave. “It is incrusted from end to end with the most beautiful formations in every variety of form. The base of the whole is sulphate of lime, in one part of dazzling whiteness and perfectly smooth, and in other places crystallized so as to glitter like diamonds in the light. Growing from this, in endless diversified forms, is a substance resembling selenite, translucent and imperfectly laminated. Some of the crystals bear a striking resemblance to celery, and all are of about the same length; while others, a foot or more in length, have the color and appearance of vanilla cream candy; others are set in sulphate of lime, in the form of a rose; and others still roll out from the base in forms resembling the ornaments on the capital of a Corinthian column. Some of the incrustations are massive and splendid; others are as delicate as the lily, or as fancy work of shell or wood.” Proctor's arcade is a magnificent natural tunnel three fourths of a mile long and 100 ft. wide, covered by a ceiling of smooth rock, 45 ft. high. The Temple or Chief City is a chamber having an area of between four and five acres, and covered by a single dome of solid rock 120 ft high. Lucy's dome, the highest of the objects of this class, is over 300 ft. high and about 60 ft. in its greatest diameter. Mammoth dome and Stella's dome are each about 250 ft. high, while Gorin's dome is about 200 ft. Sidesaddle pit, over which rests a dome 60 ft high, is about 90 ft. deep and 20 ft. across. This and some of the other pits and domes in the cave have been formed out of the solid rock by the solvent action of water charged with carbonic acid. The deepest of the pits are the Maelstrom, 175 ft. in depth and 20 in diameter, and the Bottomless pit, of about the same depth. There are several bodies of water in the cave, the most considerable being Echo river, which is about three fourths of a mile long, 200 ft. wide at some points, and from 10 to 80 ft. deep; its course is beneath an arched ceiling of smooth rock about 15 ft. high. This river has invisible communication with Green river, the depth of water and the direction of the current in the former being regulated by the stage of water in the latter. The river Styx, 450 ft. long, 15 to 40 wide, and from 30 to 40 deep, is spanned by an interesting natural bridge about 80 ft. above it. Lake Lethe is about 450 ft. long and from 10 to 40 wide, and varies in depth from 3 to 30 ft.; it lies beneath a ceiling about 90 ft. above its surface; its waters sometimes rise to the height of 60 ft., in consequence of freshets in Green river. The Dead sea is a gloomy body of water somewhat smaller than the preceding. Two remarkable species of animal life are found in the cave, in the form of an eyeless fish and an eyeless crawfish, which are nearly white in color. Another species of fish has been found with eyes, but totally blind. Other animals known to exist in the cave are lizards, frogs, crickets, rats, bats, &c., besides ordinary fish and crawfish washed in from Green river. The atmosphere of the cave is pure and healthful; the temperature, which averages 59°, is about the same in winter and summer, not being affected by climatic changes without.—The Mammoth cave was discovered in 1809, and has always been the property of private individuals. For some time after its discovery saltpetre was made here. In this vicinity are also Proctor's cave, about 3 m. in length; White's cave, Diamond cave, and Indian cave, each about a mile long. Several accounts of this wonderful curiosity have been published, the most recent and complete being “The Mammoth Cave,” by W. Stump Forwood (Philadelphia, 1870).