88 IGNEOUS AGENCIES. 



extinct volcanoes. Vesuvius, until the great eruption which overthrew 

 the ancient cities of Herculaneum and Pompeii, was regarded as an ex- 

 tinct volcano. Since that time it has been very active. Krakatoa, after 

 a silence of 200 years, burst out in 1883 in the greatest eruption known. 



Size, Number, and Distribution. — Some volcanoes are among the 

 loftiest mountains on our globe. Aconcagua, in Chili, is 23,000 feet, Co- 

 topaxi, in Peru, 19,660 feet in height. These volcanic cones, however, 

 are situated on a high plateau ; their height, therefore, is not due to vol- 

 canic eruptions entirely. But Mauna Loa, in Hawaii, nearly 14,000 feet, 

 and Mount Etna, 11,000 feet high, seem to be due entirely, and Mount 

 Shasta, California, 14,440 feet, Kainier, State of Washington, 14,444, al- 

 most entirely to this cause. The crater of Mauna Loa is two and a half 

 miles across ; that of Kilauea three miles across and 1,000 feet deep. 



The number of known volcanoes, according to Humboldt, is 407, 

 and of these 225 are known to have been active in the last 160 years. 

 The actual number is, however, probably much greater. It has been 

 estimated that, in the archipelago about Borneo alone, there are 900 vol- 

 canoes.* The distribution of volcanoes is remarkable, (a.) They are 

 almost entirely confined to the vicinity of the sea. Two thirds of them 

 are found on islands in the midst of the sea, and the remainder, with 

 the exception of a few in the interior of Asia, are near the sea-coast. 

 Those on islands in the sea, probably commenced, most of them, at the 

 bottom of the sea, the islands having been formed by their agency. 

 New islands have been suddenly formed under the eye of observers in 

 the Mediterranean and in the Pacific Ocean. The basin of the Pacific 

 is the great theatre of volcanic activity, nearly seven eighths of all 

 known volcanoes being situated on its coasts or on islands in its midst. 

 (b.) Volcanoes are, moreover, distributed in groups (as the Hawaiian 

 volcanoes, the Mediterranean volcanoes, the Icelandic volcanoes, the 

 West Indian volcanoes, the volcanoes of Auvergne, etc.), or along ex- 

 tensive lines as if connected with a great fissure of the earth's crust. 

 The most remarkable linear series of volcanoes is that which belts the 

 Pacific coast. Commencing with the Fuegian volcanoes it runs along 

 the whole extent of the Andes, then along the Cordilleras of Mexico, 

 the Kocky Mountains, then along the Aleutian chain of islands, Kamt- 

 chatka, the Kurile Islands, Japan Islands, Philippines, New Guinea, 

 New Zealand, to the antarctic volcanoes Mounts Erebus and Terror, 

 thence back by Deception Island to Fuegia again, thus completely en- 

 circling the globe, (c.) Volcanoes are generally formed in compara- 

 tively recent strata. This seems to be connected with their relation 

 to the sea ; for recent strata are abundant about the sea-coast, and the 

 most recent are now forming in the bed of the sea. The extinct vol- 



* Herschel, Physical Geology, p. 113. 



