DISTRIBUTION 35 



We cannot definitely determine the number of vents which are 

 at present in activity in various regions of the earth, because a 

 volcano may remain dormant for centuries, and then break out 

 again. Almost all tradition of the Volcanic nature of Vesuvius had 

 died away among the inhabitants of Italy, until the dreadful erup- 

 tion of the year 79 a.d. showed that it had only been slumbering. 

 Many volcanic regions, such as the western part of North and 

 South America, and the East Indian islands, have been known to 

 civilized man for only a few centuries, and in such regions the dis- 

 tinction between dormant and extinct vents cannot always be made. 



Furthermore, the number of vents is constantly changing, new 

 openings forming, and old ones closing up, while some that had 

 escaped observation are not infrequently discovered. Another 

 distinction which is often arbitrary, is that between independent 

 volcanoes and mere subsidiary vents connected with larger ones. 

 Several submarine volcanoes have been observed, but it is alto- 

 gether probable that many more exist which have escaped detec- 

 tion. Making these allowances, the number of volcanoes now 

 active may be estimated at about 328, of which rather more than 

 one-third are situated in the continents, and the remainder on 

 islands. 



The active volcanoes are not scattered hap-hazard over the sur- 

 face of the globe, but are arranged in belts or lines, which bear a 

 definite relation to the great topographical features of the earth. 

 Two of these belts together encircle the Pacific Ocean ; one on 

 the west coast of the Americas runs from Alaska to Cape Horn, 

 the other, a very long and sinuous band, running from Kamchatka 

 through the islands parallel to the east coast of Asia, the East 

 Indian and south Pacific islands, to the Antarctic circle, where it 

 joins the American band. 



A third band occupies a ridge in the eastern be"d of the Atlantic, 

 from Iceland to St. Helena, from which arise numerous volcanic 

 islands and submarine vents. South of Iceland there are no 

 known volcanoes for a great distance, until the Azores are reached, 

 and on the east coast of the Americas are none at all. A subsidi- 

 ary volcanic belt passes through the Mediterranean to Asia Minor, 



