But if the great medial chain of the Atlantic presents us with an example of a chain of volcanic mountains verging on extinction, we have in the line of islands separating the Pacific and Indian Oceans an example of a similar range of volcanic vents which are in a condition of the greatest activity. In the peninsula of Kamtschatka there are twelve active volcanoes, in the Aleutian Islands thirty-one, and in the peninsula of Alaska three. The chain of the Kuriles contains at least ten active volcanoes; the Japanese Islands and the islands lying to the south of Japan twenty-five. The great group of islands lying to the south-east of the Asiatic continent is at the present time the grandest focus of volcanic activity upon the globe. No less than fifty active volcanoes occur here. Farther south, the same chain is probably continued by the four active volcanoes of New Guinea, one or more submarine volcanoes, and several vents in New Britain, the Solomon Isles, and the New Hebrides, the three active volcanoes of New Zealand, and possibly by Mount Erebus and Mount Terror in the Antarctic region. Altogether, no less than 150 active volcanoes exist in the chain of islands which stretch from Behring's Straits down to the Antarctic circle; and if we include the volcanoes on Indian and Pacific islands which appear to be situated on lines branching from this particular band, we shall not be wrong in the assertion that this great system of volcanic mountains includes at least one half of the habitually active vents of the globe. A third series of volcanoes starts from near the last in the neighbourhood of Behring's Straits, and stretches along the whole western coast of the American continent. In this great range there are about eighty active volcanoes. [Sidenote: LINEAR ARRANGEMENT OF VOLCANOES.] In considering the facts connected with the distribution of volcanoes upon the globe, the one which, by its striking character, seems to demand our attention in the first instance is that of the remarkable linear arrangement of volcanic vents. We have already seen that small scoria-cones are often thrown up on the flanks, or at the base, of a great volcanic mountain, along lines which are manifestly lines of fissure. In the eruption of Etna, in 1865, and again in that of 1874, Professor Silvestri, of Catania, witnessed the actual opening of great fissures on the north-east and north sides of the mountain: and along the bottom of these cracks the glowing lava was clearly visible (fig. 84, page 194). In the course of a few days, there were thrown up a number of small scoria-cones along these lines of fissure--those formed on the fissure of 1865 being seven in number, and those on the fissure of 1874 being no less than thirty-six in number. Precisely familiar phenomena were witnessed upon the slopes of Vesuvius, in 1760, when a fissure opened on the south side of the mountain, and fifteen scoria-cones, which are still visible, were thrown up along it.