ON VOLCANOES AND EARTHQUAKES. 357 



found in those islands ; and, in the Pacific, I have 

 already shown that they have brought up from the 

 deep, the much more recent coral rocks. Where 

 the original rocks cannot actually be discovered in 

 their places, they are sometimes inferred from ob- 

 serving the unmelted matters ejected during erup- 

 tions ; and thus it is inferred, that granite, micaceous 

 schist, and primary limestone, lie beneath the present 

 materials of Vesuvius. 



On the Action of Volcanoes. 



The action of Volcanoes is generally periodical or 

 intermitting. Yet Stromboli is not only now in a 

 state of constant activity, but is known to have been 

 so since the year 292 before the Christian aera. Jo- 

 rullo has also continued to flame ever since it first 

 broke out. Vesuvius has been known to remain in- 

 active for centuries. JEtna and Teneriffe have also 

 intermitted for a century together ; and Vulcano was 

 free of eruptions for eleven hundred years. 



The appearances which attend eruptions are various, 

 and, in some points, instructive ; but as I can only 

 give a meagre sketch, I must refer to the endless 

 descriptions of authors. As the consequences are no 

 less terrific than picturesque, they have not only led 

 to highly coloured descriptions, but have misled and 

 dazzled those whose minds were not steadily bent on 

 realities. 



The most simple and precise account is that given 

 of Stromboli by Spallanzani. The crater of this vol- 

 cano always contains melted lava, in constant motion. 

 On a sudden it becomes raised to a higher level, and 

 when it arrives near the edge of the basin, a sound 

 resembling thunder is heard, and a portion of the lava 

 is thrown up into the air, accompanied by dust and 



