CHAPTER XII.

ON CAVES IN GENERAL.

Their various Forms—Natural Tunnels—The Ventanillas of Gualgayoc—Eimeo—Torgatten—Hole in the Mürtschenstock—The Trebich Cave—Grotto of Antiparos—Vast Dimensions of the Cave of Adelsberg and of the Mammoth Cave—Discovery of Baumann’s Cave—Limestone Caves—Causes of their Excavation—Stalactites and Stalagmites—Their Origin— Variety of Forms—Marine Caves—Shetland—Fingal’s Cave—The Azure Cave—Cave under Bonifacio—Grotta di Nettuno, near Syracuse—The Bufador of Papa Luna—Volcanic Caves—The Fossa della Palomba—Caves of San Miguel—The Surtshellir 133