Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/652

Rh 628 ETNA researches iu a paper communicated to the Royal Society, and in a lengthy chapter in his Principles of Geology. His investigations have contributed much to our know ledge of the geological characteristics of the mountain. The most important recent contribution to our knowledge of Etna has been the fine map of the Stato Maggiore con structed by order of the Italian Government between 1864 and 1868. It embraces the whole of Sicily, and is laid down on the unusually large scale of 1 in 50,000, or T266 inch to the mile. The portion relating to Etna and its immediate surroundings occupies four sheets. Plate VII. is a reproduction of this map on a smaller scale. All the Binall roads, paths, and rivulets are introduced ; the minor cones and monticules are placed in their proper positions; and the elevation of the ground is given at short intervals of space over the map. A careful examination of this map shows us that it represents the first accurate survey of the entire mountain. It shows us that distances, areas, and heights have been repeatedly misstated, the minor cones misplaced, and the trend of the coast-line misrepresented Height. The height has been often determined. The earlier writers had very exaggerated notions on the subject, and a height of three and even four miles has been assigned. Brydone, Saussure, Shuckburgh, and others obtained ap proximations to the present height ; it must be borne in mind, however, that the cone of a volcano is liable to variations in height at different periods, and a diminution of more than 300 feet has occurred during the course of a single eruption of Etna, owing to the falling of the cone of cinders into the crater. During the last sixty years, how ever, the height of the mountain has been practically con stant. In 1815 Captain Smyth determined it to be 10,874 feet. In 1826 Sir John Herschel, who was unacquainted with Smyth s results, estimated it at 10,872| feet. The new map of the Stato Maggiore gives 3312 61 metres = 10,867 9 i feet. The radius of vision from the summit is very variously stated. Smyth gives it as 150 7 miles, and this we are inclined to adopt as the nearest approach to the truth, because he was an accurate observer, and he made careful corrections both for error of instruments and for refraction. This radius gives an horizon 9 46 4 miles in circumference, and an included area of 39,900 square miles, an area larger than that of Ireland. . Boundaries. The road which eurronnds the mountain ia carried along its lower slopes, and is 87 miles in length. By reference to the map it will be seen that it passes through the towns of Patern6, Biancavilla, Aderno, Bronte, Randazzo, Linguaglossa, Giarre, and Aci Reale. By some writers it is considered to define the base of the mountain, which is hence said, most erroneously, to have a circumference of 87 miles ; but the road frequently passes over high beds of lava, and it winds considerably. It id about 10 miles from the crater on the north, west, and east sides of the mountain, increasing to 16 miles at Pu,tern6 (S.W.). The elevation on the north and west flanks of the mountain is nearly 2500 feet, rising at its maximum elevation to 3852 feet, while on the south it falls to 1500 feet, and on the east to within 50 feet of the level of the sea. It is quite clear, therefore, that this road cannot be taken as the limit of the base. The natural boundaries of Etna are the rivers Alcantara and Simoto on the north, west, and south, and the sea on the east to the extent of 23 miles of coast, along which lava streams have been traced, sometimes forming headlands several hundred feet in height. The base of the mountain, as denned by these boundaries, is said to have a circumference of &quot; at least 120 miles ; &quot; an examination of the new map, however, proves that this is overestimated. If we take the sea as the eastern boundary, the river Alcantara (immediately beyond which Monte i;i Mojo, the most northerly minor cone of Etna, is situated) as the northern boundary, and the river Simeto as the boundary on the east and south, we obtain an approximate circumference of 91 miles for the base of the mountain. In this estimate the small sinuosities of the rivers have been neglected, and the southern circuit has been completed by drawing a line from near Patern6 to Catania, because the Simeto runs for the last few miles of its course through the plain of Catania, quite beyond the most southerly lava stream. Area. The area of the region inclosed by these boundaries is approximately 480 square miles. Reclus gives the area of the mountain as 1200 square kilometres = 461 square miles (Nouvelle Geographic Universelle, 1875). Population. There are 2 cities, Catania and Aci Reale, and 63 towns or villages on Mount Etna, It is far more thickly populated than any other part of Sicily or Italy ; for while the population of Italy per square kilometre is 90, and of Sicily 88, that of the habitable zone of Etna is 550. N&quot;o less than 300,000 persons live on the mountain. Thus, with an area rather larger than that of Bedfordshire (462 square miles), it has more than double the population ; and with an area equal to about one-third that of Wiltshire, the population of the mountain is greater by nearly 50,000. General Aspect. The general aspect of Etna is that of a pretty regular cone with very gentle slopes covered with vegetation, except near the summit. The regularity is broken on the east side by a slightly oval valley, four or five miles in diameter, called the Val del Bue. It com mences about two miles from the summit, and is bounded on three sides by nearly vertical precipices from 3000 to 4000 feet in height. The bottom of the valley is covered with lavas of various dates, and several minor craters hav- froru time to time been upraised from it. Many erupt iuiis have commenced in the immediate neighbourhood of the Val del Bue, and Lyell believes that there once existed a crater of permanent eruption in the valley. Mount Vesuvius might be almost hidden away in the Val del Bue. Reyions. The Val del Bue is altogether sterile, having been the frequent scene of both fire and flood, but the mountain at the same level, as its middle and lower portions, is on its other sides clothed with forests. The surface of the mountain has been divided into three zones or regions the Piedemontana or Coltivata, the Selvosa or J^emorosa, and the DeserLa or Discoperta. The lowest of these, the Cultivated Region, yields in abundance all the ordinary Sicilian products. The surface soil, which consists of decomposed lavas, is extremely fertile, although of course large tracts of land are covered by recent lavas, or by those which decompose but slowly. In this region the vine flourishes, and abundance of corn, olives, pistachio nuts, mulberrie*, oranges, lemons, figs, and other fruit-trees. The breadth of the Coltivata vanes; it terminates at an approximate height of 2000 feet. A circle drawn with a radius of ten miles from the crater roughly defines the upward limit of this region. The elevation of points on the circumference of such a circle is 2310 feet on the north near Randazzo, 2145 feet on the south near Nicolosi, 600 feet on the east near Mascali, and 1145 feet on the west near Bronte. The breadth of the cultivated zone is about two miles on the north, east, and west, and nine or ten miles on the south, if we taJe for the base of the mountain the limits proposed above. The Woody Region commences where the Cultivated Region ends, and it extends as a belt of varying width to an approximate height of 6300 feet. It is terminated above by a circle having a radius of about a mile and a half from the great crater. There are fourteen separate forests in this region, some abounding with oak, beech, pine, a&d poplar, others with the chestnut, ilex, and cork tree. The celebrated Castagno di Cento Cavalli, one of the largest