The old continent also affords innumerable examples; along the whole coast of Norway, from North Cape southwards, there is a continuous chain of rocky islands similar and parallel to the great range of the Scandinavian Alps; Great Britain itself, with the Hebrides, Orkney, and Zetland islands, are remarkable instances of Continental islands. It would be superfluous to mention the various instances which occur in the Mediterranean, where many of the islands are merely the prolongations of the mountain-chains of the mainland rising above the sea, as Corsica and Sardinia, which are a continuation of the Maritime Alps. The great central chain of Madagascar and its elongated form, parallel to the Lupata Mountains, show that the island once formed part of the African continent. Asia, also, abounds in instances, as Sumatra, Java, and the Moluccas, and another vast chain extends along the western coast of Asia from Formosa to Kamtchatka. Pelasgic islands have risen from the bed of the ocean, independently of the continents, and generally far from land. They are mostly volcanic, altogether or in part; often very lofty; sometimes single, and frequently in groups, and each group has, or formerly has had, a centre of volcanic action in one or more of the islands, round which the others have been formed. Many have craters of elevation, that is to say, they have been raised up in great hollow domes by the internal elastic vapours, and have either remained so, have become rent at the surface into gigantic fissures, or have collapsed into hollow cups, in which craters have formed, by the eruption of loose incoherent matter, or of lava currents, when the pressure from below was removed:[74] a considerable number have active vents. The small islands and groups scattered at enormous distances from one another, within the Antarctic Circle, are all of volcanic formation, though none are active. In the Atlantic, Tristan da Cunha, St. Helena, Ascension, and Madeira are volcanic, though not now actively so; whereas the Cape de Verde, Canaries, and Azores have each volcanic vents: the peak of Teyda, in Teneriffe, is one of the most magnificent volcanic cones in the world. The labyrinth of islands scattered over the Pacific Ocean for more than 30 degrees on each side of the equator, and from the 130th eastern meridian to Sumatra, which all but unites this enormous archipelago to the continent of Asia, has the group of New Zealand or Tasmania, and the continent of Australia, with its appendage, Van Diemen’s Land, on the south, and altogether forms a region which, from, the unstable nature of the surface of the earth, is partly the wreck of a continent that has been engulfed by the ocean, and partly the summits of a new one rising above the waves. This extensive portion of the globe is in many parts terra incognita; the Indian Archipelago has been little explored, and, with the exception of our colonies in New Holland and New Zealand, is little known.