One of the best examples of a submarine eruption resulting in the formation of a temporary island occurred in 1831 in the Mediterranean between Sicily and the coast of Africa, where the water was known to have previously had a depth of ioo fathoms. After the usual manifestations of volcanic activity an accumula tion of black cinders and ashes formed an island which reached at one point a height of 200 ft., so that the pile of erupted matter had a thickness of about Boo feet. The new island, which was studied by Constant Prevost, became known in England as Gra ham's Island, in France as Ile Julie and in Italy by various names, among them Isola Ferdinandea. Being merely a loose pile of scoriae, it rapidly suffered erosion by the sea, and in about three months was reduced to a shoal called Graham's Reef. In the year 1891 a submarine eruption occurred in the neighbourhood of the isle of Pantellaria in the same waters, but it gave rise to no island. A well-known instance of a temporary volcanic island was fur nished by Sabrina—an islet of cinders thrown up by submarine eruptions in 181i, off the coast of St. Michael's, one of the Azores. The island of Bogosloff, or Castle Island, in Bering Sea, about 40 m. W. of Unalaska Island, is a volcanic mass which was first ob served in 1796 after an eruption. In 1883 another eruption in the neighbouring water threw up a new volcanic cone of black sand and ashes, known as New Bogosloff or Fire Island, situated about m. N.W. of Old Bogosloff, with which it was connected by a low beach.
It is a matter of frequent observation that volcanoes are most abundant in regions marked by great seismic activity. Although the volcano and the earthquake are not usually connected in the direct relation of cause and effect, yet in many cases they seem referable to a common origin. Both volcanic extrusion and crustal movement are means of relieving local strains in the earth's crust, and both are found to occur, as might reasonably be expected, in many parts of the earth where folding and fracture of the rocks have frequently happened and where mountain-making appears to be still in progress. Thus, volcanoes may often be
traced along zones of crustal deformation, or folded mountain chains, especially where they run along the oceanic basins.
The most conspicuous example of linear distribution is furnished by the great belt of volcanoes, which engirdles intermittently the huge basin of the Pacific ; though here, as elsewhere in study ing volcanic topography, regard must be paid to dormant and extinct centres as well as to those that are active at the present. time. As volcanoes are in many cases ranged along what are com monly regarded as lines of fracture, it is not surprising that the centres of most intense vulcanicity are in many cases situated at the intersection of two or more fracture-lines. On the eastern side of the Pacific the great volcanic ring may be traced, though with many interruptions, from Cape Horn to Alaska. In South America the chain of the Andes between Corcovado in the south and Tolima in the north is studded at irregular intervals with volcanoes, some recent and many more extinct, including the loftiest volcanic mountains in the world. The grandest group of South American volcanoes, though mostly quiescent, is in Ecuador. Cotopaxi, seen in activity by E. Whymper in 188o, has, according to him, a height of 19,613 ft., whilst Sangay is said to be one of the most active volcanoes in the world. The volcanic rock called andesite was so named by L. von Buch from its characteristic occurrence in the Andes. It is notable that the volcanic rocks throughout the great Pacific belt present much similarity in composition. The volcanoes of Ecuador have been described in detail by A. Stiibel and others (see ANDES). Central America contains a large number of active volcanoes and solfa taras, many of which are located in the mountains parallel to the western coast ; Guatemala is peculiarly rich in volcanoes, as de scribed by Dr. Tempest Anderson, who visited the country in 1907; and the plateau of Mexico is the seat of several active volcanoes which occur in a band stretching across the country from Colima in the west to Tuxtla near Vera Cruz. The highest of these is Orizaba (18,20o ft.), which is known to have been active in the 16th century. Popocatepetl ("the smoking moun tain") reaches a height of about 17,88o ft., and from its crater sulphur was at one time systematically collected. The famous volcano of Jorullo, near Toluca and about 120 m. from the sea, has been the centre of much scientific discussion since it was re garded by Humboldt, who visited it in 1803, as a striking proof of the elevation theory; it came into existence rapidly during an eruption which began in Sept. 1759, when it was said by un scientific observers that the ground became inflated from below.