CAVES

or CAVERNS (Lat. cavus, hollow), hollow places formed in the berth or in rock. They may be produced ay the action of water or by the destruction and displacement of strata through an earthquake or landslip. The regular beating of waves upon the seashore wears away the softer portion of the cliff until Cavities are formed. Fingal’s C., Staff a, is an excellent example of marine erosion. The sand and gravel, carried up by the sea, have also a great eroding wer upon rocks. In rock-salt districts caves are formed owing to the free solubility of the sodium chloride in water. In France and Switzerland large caverns have been formed under glaciers, Owing to the shifting of the ice. C. are, however, more frequently formed by the chemical than by the mechanical action of water. Carbonic acid, which is present in most waters, derived either from the air or from decaying organic matter in the soil, acts upon mineral rock forming salts, which are carried away in solution, leaving cavities behind. Large subterranean galleries, caverns, and channels have been formed in various districts by underground streams and rivers. A river that has left its course above ground eats its way through the earth, until it can finally empty itself into the sea. Whenever such a river, for some natural cause, has abandoned its subterranean watercourse, the channel it has occupied gradually dries up, and tortuous underground pa ages ) ain, linking together the C. previous made by the water. The holes through which the rivers have descended on their Ownward course below the earth are known as sink-holes. The direction of the caverns and channels can frequently be ascertained above ground by examination of these entrance-holes. Fine speciens of such sink-hoiles are found in entucky and Florida.