CAVE, or CAVERN, an opening produced by nature in the solid crust of the earth. Caves are principally met with in limestone and gyp sum as a result of the solvent action of ordinary circulating underground water. Less often they occur in sandstone, and in volcanic rocks (ba salt, lava, tufa, etc.). The form of the caves depends partly upon the nature of the substance in which they exist; but it is frequently altered by external causes. Out of some caverns rivers take their course; others again admit rivers, or may be said to swallow them for a space. There are many and various causes for the formation of caves. Those in limestone and gypsum are unquestionably the results of the dissolving power of water; in fact the almost perfectly uniform direction, the gentle and equable declivity of most caves, appear to be the effect of the long continuance of water in them, the action of which has widened the ex isting crevices. In trachyte and lava, caves appear to have been produced by the effects of gas. The caves of gypsum often contain foul air; the caves of limestone are commonly marked by various figures of stalactites, pro duced by the deposit of the lime dissolved in the water. Many of these lime caves contain remnants of bones of animals, such as hyaenas, elephants and bears. See CAVE-DWELLERS.
Many caves are remarkable only on account of their great size, or sublime from the awful gloom which pervades them, and the echoes which roll like thunder through their vaulted passages. Some are of great depth, as that of Frederikshall, Norway, calculated to be several thousand feet in depth. One of the grandest natural caverns known is Fingal's Cave (q.v.) in Staffa, one of the Western Islands of Scot land. Its sides are formed of ranges of basaltic columns which are almost as regular as hewn stone. The grotto of Antiparos, on the island of the same name, in the Grecian Archipelago, is celebrated for its magnificence. The roof is adorned with stalactites, many of them 20 feet long, and hung with festoons of various forms and brilliant appearance. In some parts im mense columns descend to the floor; others present the appearance of trees and brooks turned to marble. The Peak Cavern in Derby shire, England, is a celebrated curiosity of this kind. It is nearly half a mile in length; and, at its lowest part, 600 feet below the surface.
Other famous stalactitic caves are the Luray Cavern (q.v.), Page County, Va.; one near Ma tanzas, Cuba; one near Adelsberg, Carniola; the Wyandotte Cave (q.v.), Crawford County, Ind.; and Madison's Cave, in Rockingham County, Va. The caves of Kirkdale, in Eng land, and Gailenreuth, in Germany, are remark able for the quantities of bones of the elephant, rhinoceros and hyaena found in them. In the rock of Gibraltar there are a number of stalacti tic caverns, of which the principal is Saint Michael's Cave, many feet above the sea. Other celebrated caves in America are Weyer's Cave, in Augusta County, Va., extending 800 yards, but extremely irregular; the Colossal Cavern, Ky. (q.v.), discovered in 1895, and the Mam moth Cave (q.v.) in Edmondson County, Ky., which encloses an extent of about 150 miles of subterraneous windings. One of its chambers, called the Temple, covers a space of nearly five acres, and is surmounted by a dome of solid rock 120 feet in height. The Cumberland Mountains, in Tennessee, contain some curious caverns, in one of which, at a depth of 400 feet, a stream was found with a current sufficiently powerful to turn a mill. Another cave in the same State is named Big Bone Cave, from the bones of the mastodon which have there been discovered. In the Raccoon Mountains, near the northwestern extremity of Georgia, is Nickojack Cave, 50 feet high and 100 feet wide, which has been explored to the distance of three miles. A stream of considerable size, which is interrupted by a fall, runs through it. The Ozark region of Missouri is noted for its numerous caves, among which Onondaga cavern is perhaps the best known. Caves are some times found which exhale poisonous vapors. The most remarkable known is the Grotto del Cane, a small cave near Naples. In Iceland and Hawaii there are many caves formed by the lava from volcanoes. In the volcanic country near Rome there are many natural cavities of great extent and coolness, which are sometimes resorted to as a refuge from the heat. In South America is the cavern of Guacharo, which is said to extend for leagues. For in formation concerning human and animal re mains in caves, see CAVE-DWELLERS and consult works there referred to. See also section on work of ground water, in article on GEOLOGY.