188 



CAUSES OF VOLCANOES. 



lions, Mr. C. Darwin maintains the existence of a 

 vast internal sea of melted rock below a large part 

 of South America, and regards the submarine out- 

 bursts, the renewed volcanic activity, and the per- 

 manent elevation of the land, as forming parts of 

 one great action and effects of one great cause, 

 multiplied only by local circumstances. From the 

 phenomena of earthquakes he adduces the follow- 

 ing conclusions, which Mr. Philips thinks ought to 

 be adopted. 



1st. That the primary shock of an earthquake is 

 caused by a violent rending of the strata, which, on 

 the coast of Chili and Peru, seems generally to oc- 

 cur at the bottom of the neighbouring sea. 



2d. That this is followed by many minor frac- 

 tures, which, though extending upward, do not, ex- 

 cept in submarine volcanoes, actually reach the sur- 

 face. 



3d. That the area thus fissured extends parallel, 

 or nearly so, to the neighbouring coast mountains. 



4th. That the earthquake relieves the subterra- 

 nean force precisely in the same manner as an 

 eruption through an ordinary volcano. 



There is but one other theory in relation to vol- 

 canic action which deserves mention, and that is 

 what has been termed " the chemical hypothesis." 

 It was originally proposed by Sir Humphrey Davy, 

 in consequence of his discovery of the metallic and 

 metalloid bases of the alkalies and earths, which 

 burn when brought in contact with water. Dr. 

 Daubeny, who is now the chief supporter of this 

 view, states that, when water is brought in contact 

 with these metals, which are supposed to form the 

 interior of the earth, one part of the liquid is de- 

 composed, the metals and the chlorides will seize 

 oxygen, and be thereby converted to silica, alu- 

 mina, lime, magnesia, soda, &c, substances which 

 predominate in lavas ; the hydrogen will be libera- 

 ted in the state of gas, or, in combination with chlo- 



