GROTTO, properly GROTTA, a cave, natural or artificial, in the face of a rock or a mountain.
Among the more remarkable artificial works of this kind may be mentioned the famous Grotta di Pausilippo, which is a straight passage cut through the rock from Naples to Pozzuoli, about 1000 paces in length, 80 or 90 feet high, from 24 to 30 feet wide, and forming the main road for the daily traffic of a very populous district. See PAUSILIPPO. But the most remarkable examples of artificial caverns in the world are to be found in the ancient Petra, which may be called a city of caves or grottoes. See PETRA.
Of natural grottoes, it will only be necessary here to name a few of the most remarkable in their several ways, in order to facilitate reference to those parts of the work where they are more particularly described. Among these are the celebrated caverns of Illyria, in the Julian Alps—moun-
Group
growth. tains of calcareous formation, and abounding in caves; while they present, particularly in the eastern part, the natural phenomena of subterranean rivers, lakes, cascades, and other curiosities, such as are unknown in any other part of Europe. The most magnificent of these is described under ADELSBERG, which see. Under separate heads, or those of the countries where they occur, will be found, together with many others of note, descriptions of the following famous caves:—Baumans Höhle, a series of ossiferous caverns in Germany (see BAUMANS HÖHLE); the ossiferous cave of Kirkdale in Yorkshire (see KIRKDALE); the Mammoth Cave of Kentucky, said to be 8 or 10 miles in length (see KENTUCKY); the Epsom Salt Cave, 2 miles long (see INDIANA); the famed cavern of Antiparos, an island in the Grecian Archipelago (see ANTIPAROS). The caves and excavations of the Peak district in Derbyshire are very celebrated. An account of these is to be found in the illustrated work entitled Peak Scenery, by E. Rhodes.
The Grotta del Cane (i.e., dog's cavern) is a small cave near Puzzuoli, about 7 miles S.W. of Naples, remarkable for the noxious quality of its air. This is caused by the carbonic acid which issues from crevices in the floor of the cave, and which fills the lower part to the level of the entrance, when it flows out by its superior gravity. Hence a man may enter the cave with impunity; while a small animal, such as a dog, is speedily destroyed by the noxious gas it must necessarily respire. See CAVE, vol. vi., p. 350.