286 VOLCANIC THEORIES. [SECT. xxvi. 



any part of the surf ace, like an addition of clothing, by keeping 

 it in, would raise the temperature of the strata below, and in 

 the course of ages would even reduce those at a great depth 

 to a state of fusion. Some of the substances might be con- 

 verted into gases ; and should the accumulation of new mat- 

 ter take place at the bottom of the sea, as is generally the 

 case, this lava would be mixed with water in a state of igni- 

 tion in consequence of the enormous pressure of the ocean, 

 and of the newly super-imposed matter which would prevent 

 it from expanding into steam. Now Mr. Lyell has shown, 

 with his usual talent, that the quantity of matter carried down 

 by rivers from the surface of the continents is comparatively 

 trifling, and that the great transfer to the bottom of the 

 ocean is produced at the coast line by the action of the sea ; 

 hence, says Sir John Herschel, " the greatest accumulation of 

 local pressure is in the central area of the deep sea, while the 

 greatest local relief takes place along the abraded coast lines. 

 Here then should occur the chief volcanic vents." As the 

 crust of the earth is much weaker on the coasts than elsewhere, 

 it is more easily ruptured, and, as Mr. Babbage observes, 

 immense rents might be produced there by its contraction in 

 cooling down after being deprived of a portion of its original 

 thickness. The pressure on the bottom of the ocean would 

 force a column of lava mixed with ignited water and gas to 

 rise through an opening thus formed, and, says Sir John 

 Herschel, " when the column attains such a height that the 

 ignited water can become steam, the joint specific gravity of 

 the column is suddenly diminished, and up comes a jet of 

 mixed steam and lava, till so much has escaped that the 

 matter deposited at the bottom of the ocean takes a fresh 

 bearing, when the evacuation ceases and the crack becomes 

 sealed up." 



This theory perfectly accords with the phenomena of 

 nature, since there are very few active volcanoes at a distance 

 from the sea, and the exceptions that do occur are generally 

 near lakes, or they are connected with volcanoes on the mari- 



