Mammoth Cave
2 of the 7 encyclopedias on this shelf carry an entry for Mammoth Cave. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a celebrated cavern in Edmondson County, Kentucky. It lies about eighty-five miles southwest of Louisville. It may be reached readily by rail. Described in the simplest language, it consists of a number of immense chambers formed in the limestone rock. The material of the rock layers has been dissolved and carried away by trickling water. The main cave is three miles in length and from 40 to 175 feet in width. Its height varies from 40 to 125 feet. A dome-shaped enlargement of this cave is oval in shape. It is 540 feet in length by 287 feet in width, and is 125 feet high. Stone arrowheads, remnants of torches, and other relics found here, show that it was an ancient meeting-place of the Indians. The entire series of caverns, known as the Mammoth Cave, exists in five different layers of rock, communicating one with another by means of pits and passages. A number of artificial shafts have been cut for the accommodation of visitors. About 150 miles of passageways have been mapped. The diameter of the district is about ten miles. Other regions branching off are as yet unexplored. There are numerous lakes and several underground streams. The largest of these is called Echo River, because of its echoes. Boats are offered by competent guides. The waters abound in fish that have been deprived of light so long that they have lost their eyesight. Crawfish, crickets, flies, beetles, and spiders found in the caves, where they have lived no doubt for many generations, have also lost the use of their eyes. Countless numbers of bats take refuge near the mouth of the cave. A trip through the cave is by no means disagreeable. Intense darkness prevails, but the air is pure and clear. Guides light up the way so that the wonderful stalactites, stalagmites, domes, pits, and channels may be seen clearly. One room, known as the Star Chamber , has a lofty black ceiling studded with clusters of snowy crystals. The temperature remains constant throughout the year at about 54 deg. F. The cavern is owned by private parties, but a movement is on foot to make it a state park. See Cave
Collier's New Encyclopedia (1921)
a cavern near Green river, Edmonson co., Ky., about 85 miles S. S. W. of Louisville. The cave is about 10 miles long, but it requires upward of 150 miles of traveling to explore its multitudinous avenues, chambers, grottoes, rivers, and cataracts. The main cave is 4 miles long, from 40 to 300 feet wide, and rises in height to 125 feet. The most interesting features of the cave are: The Chief City or Temple, covering an area of about four acres, and having a dome of solid rock 120 feet high; the Star Chamber, about 500 feet long by 70 feet wide, with a ceiling 70 feet high, consisting of black gypsum dotted with many white points which, when the chamber is lighted, have all the appearance of stars; Silliman's avenue, 1½ miles long, 20 to 200 feet wide , and 20 to 40 feet high; Cleveland's Cabinet , an arch 50 feet wide, 10 feet high, and 2 miles long, covered with a variety of formations in all sorts of shapes and of many colors; the Maelstrom Abyss and Bottomless Pit, each of which is 20 feet wide and about 175 feet deep, and the river Styx, 450 feet long and crossed by a natural bridge about 30 feet high. The cave contains various kinds of animals, and there are also found lizards, crickets, frogs, bats, and different sorts of fish. The latter include the famous eyeless fish, which are white in color. The Mammoth Cave is supposed to have been discovered in 1809. The atmosphere is pure and healthful and there is a temperature throughout the year of about 59°. It is visited annually by many sightseers.