GEOLOGY. - ()55 



surface of the globe. But by this it is not meant that they 

 are agitated by perpetual convulsions. Nearly all awake 

 to their terrible activity only at long intervals^ and during 

 the space of time between the eruptions their internal toil 

 is only revealed by slight and deceptive phenomena. 



When a formidable eruption breaks out it is often ac- 

 companied by didl roars which seem to shake the moun- 

 tain. In a short time the fiery mouth launches into the 

 air sheets of flame and smoke, as well as masses of cinders 

 and burning rock; in 1553, in one of its most terrible erup- 

 tions, Cotopaxi projected to a distance of three leagues 

 blocks of trachyte a hundred cubic metres (a cubic metre 

 is 35 SIT cubic feet) in size. During this time the lava 

 escapes with violence from the enti-ails of the mountain, 

 and pours over its sides like so many streams or cascades 

 of fire, consuming everything in their path. 



In very lofty volcanoes the lava, in order to rise to the 

 crater in which they culminate, must require an almost 

 incalculable force; hence it often happens that it makes its 

 way out before reaching it, and having burst the flanks of 

 the mountain near its base forms a small additional volcano, 

 in which, for the future, all the efforts of the eruption are 

 concentrated, and from which pour streams of lava of a 

 magnitude we should not expect from so low an elevation. 



In high volcanic mountains we often find at the base 

 of the great cone a series of small accessory volcanoes : as 

 we have seen, Etna possesses cjuite a family scattered over 

 its flanks. In fact it is these that have in particular 

 ravaged the surrounding countries. 



The most frightful eruption of Etna in modern times 

 Avas produced by one of these young volcanoes, the ]\Ionte 

 Eosa. From it issued the long river of lava which rolled 

 its burning waves over a distance of nine leagues, fired 



