Through the great island of Sumatra, a chain of volcanoes runs longitudinally, and may possibly be continued northwards in the , Bay of Bengal by Barren Island and Narcondam—the former an active and the latter an extinct volcano. On the western side of the Indian Ocean a small volcanic band may be traced in the islands of the Mascarene group, several craters in Reunion (Bour bon) being still active. Far south in the Indian Ocean are the volcanic islands of New Amsterdam and St. Paul. The Comoro Islands in the channel of Mozambique exhibit volcanic activity, whilst in East and Central Africa there are several centres, mostly extinct but some partially active, associated with the Rift Val leys. The enormous cones of Kenya and Kilimanjaro are extinct, hut on one of the summits of the latter, a crater is still preserved. The Mfumbiro volcanoes, S. of Lake Edward, rise to a height of more than 14,700 feet. Kirunga, N. of Lake Kivu, is still par tially active. Elgon is an old volcanic peak, but Ruwenzori is not of volcanic origin. On the west side of Africa, the Cameroon Peak is a volcano which was active in 1909, and the island of Fernando Po is also volcanic. Along the Red Sea there are not wanting several examples of volcanoes, such as Jebel Teir, the Twelve Apostles islands, and Aden, which is situated on the wreck of an old volcano.
Passing to the Atlantic, a broken band of volcanoes, recent and extinct, may be traced longitudinally through certain islands, some of which rise from the great submarine ridge that divides the ocean, in part of its length, into an eastern and a western trough. The northern extremity of the series is found in Jan Mayen, an island in the Arctic, where an eruption occurred in 1818. Iceland, however, with its wealth of volcanoes and geysers, is the most important of all the Atlantic centres : according to Dr. T. Thoroddsen there are in Iceland about 13o post-glacial volcanoes, and it is known that from 25 to 3o have been in erup tion during the historic period. Many of the Icelandic lava-flows, such as the immense flood from Laki in 1783, are referable to fissure eruptions, which are the characteristic though not the exclusive form of activity in this island. This type was also
responsible for the sheets of old lava in the terraced hills of the Faroe Islands, and the Tertiary eruptions of the west of Scotland and the north of Ireland.
An immense gap separates the old volcanic area of Britain from the volcanic archipelagos of the Azores, the Canaries and the Cape Verde Islands. The remaining volcanic islands of the Atlantic chain, all now cold and silent, include Ascension, St. Helena and Tristan da Cunha.
An interesting volcanic region is found in the West Indies, where the Lesser Antilles—the scene of the great catastrophes of 1902—form a string of islands, stretching in a regular arc that sweeps in a N. and S. direction across the E. end of the Carib bean. Subject to frequent seismic disturbance, and rich in vol canoes, solfataras and hot springs, these islands seem to form the summit of a great earth-fold which, rising as a curved ridge from deep water, separates the Caribbean from the Atlantic. The volcanoes are situated on the inner border of the curve.
Vesuvius is the only active volcano on the mainland of Europe but in the Mediterranean there are Etna on the coast of Sicily; the Lipari Islands, with Stromboli and Vulcano in chronic activ ity ; and farther to the east the archipelago of Santorin, which has erupted recently. Submarine eruptions have occurred also between Sicily and the coast of Africa; one in 1831 having—as we have seen above—given rise temporarily to Graham's Island, and another in 1891 appearing near Pantellaria, itself a volcanic isle. Of the extinct European volcanoes, some of the best known are in Auvergne, the Eifel, Bohemia and Catalonia, whilst the volcanic land of Italy includes the Euganean hills, the Alban hills, the Phlegraean Fields, etc.
The number of volcanoes known to be actually active on the earth is generally estimated at between 30o and 400, but there is reason to believe that this estimate is far too low. If account be taken of those volcanic cones which have not been active in his toric time, the total will probably rise to several thousands.