168 Volcanoes. 



Active Volcanoes may be divided into aerial * and sub- 

 aqueouSj or those which have their craters exposed to the 

 action of the air, and those which are under the water. There 

 must be a considerable difference between the phenomena 

 which attend these classes ; namely, in proportion to the 

 density of the obstructing medium. At present, however, 

 our knowledge of the phenomena which attend subaqueous 

 activity is exceedingly circumscribed : we shall, however, 

 separately consider the phenomena which precede and accom- 

 pany the activity of these two classes of active volcanoes. 



The points of enquiry that most forcibly strike the atten- 

 tion, when thinking upon the volcanic agent, are the pheno- 

 mena which precede and attend its activity, the geographical 

 position of volcanic mountains, and the character of the sub- 

 stances they eject. We are then, by a natural train of thought, 

 led to enquire what can be the cause of these destructive phe- 

 nomena, and what the methods by which volcanic mountains 

 are formed and destroyed. These are the subjects which will 

 chiefly demand our attention in the following pages ; and will, 

 we hope, develope all the most important and striking facts 

 connected with the subject. 



The Phenomena nxihich precede volcanic Action. — In every 

 age of the world there have been some who, separating them- 

 selves in part from the common amusements of mankind, 

 have devoted their leisure to the investigation of natural phe- 

 nomena. These have searched into the secrets of Almighty 

 Intelligence, and gazed in admiration upon the beauty of his 

 creatures, and the contrivance displayed in their formation. 

 But the more solemn and destructive of his agents, in their 

 moments of sublime excitement, have drawn the attention of 

 those who were unimpressed by Nature in her periods of 

 beautiful repose. The accuracy of this remark will be ad- 

 mitted by those who have never witnessed a more violent dis- 

 turbance than a passing thunder-storm ; but how much more 

 fully would it be received by those who have gazed on their 

 native hills when torn by the impetuous tide of subterranean 

 fire ! It is the importance which all men attribute to unfre- 

 quent phenomena, and particularly when of a fearful charac- 

 ter, whether they are seen, or known by tradition, that has 

 furnished us with an ample fund of information concerning 

 the many volcanic mountains with which every quarter of the 

 globe abounds. 



* We have preferred the term aerial to sub-aerial, because the subaque- 

 ous may be said to be under the air as well as those exposed to the action 

 of the atmosphere. 



