THEORIES OF VOLCANIC ACTION. 61 



chinks and fissures that admit the percolation of water 

 down to the incandescent mass, are ascribed the tremors 

 and convulsions of the earthquake and the sudden explo- 

 sions of the volcano. By the latter hypothesis it is pre- 

 sumed that the solid crust contains abundance of metallic 

 elements, such as potassium, sodium, calcium, magnesium, 

 and the like, and that the percolating waters coming in 

 contact with these produce instantaneous combinations, 

 which result in uncontrollable manifestations of heat, and 

 the conversion of these metals into their oxides potash, 

 soda, lime, magnesia, &c. which enter largely into the 

 composition of the rock-matter ejected at the surface. Such 

 is a brief and general view of the two leading hypotheses 

 that have been advanced to account for vulcanic pheno- 

 mena. The adherents of the former question the presence 

 of these metallic elements in such abundance as to produce 

 such gigantic results, and point to the universality of vol- 

 canic action and the uniformity of its products as evidences 

 of its arising from the same great interior source. The 

 adherents of the latter contend for a system of action and 

 reaction, without which the globe would gradually lose its 

 supposed interior heat, and become so cool that in process 

 of time volcanic action would cease a result incompatible 

 with the maintenance of a diversified and habitable surface. 

 According to the mechanical theory, say they, the interior 

 heat must be gradually declining, and must finally come to 

 an end ; but according to the chemical, there is a round of 

 incessant action and reaction, a system of compensation 

 and endurance which accords with the other ordainings of 

 the universe. This is not the place to do more than merely 

 allude to these contending views, our object in these sketches 

 being rather to explain what is known than to discuss 

 what is questionable. 



But whatever be the origin of vulcanic force, we see it 



