150 ON THE CHARACTRES AND DISPOSITION 



now to be found in that situation; which it is not. 

 This is a proposition apparently very simple ; but the 

 simplicity of a proposition ought to be well ascer- 

 tained before it is advanced as such. 



In the phenomena that attend volcanoes, which 

 were just noticed, it seems certain that volcanic matter 

 is sometimes moved, or perhaps introduced among 

 the strata, without appearing at the surface. The 

 cause is here indicated by that eruption of rock which 

 takes place at a distant point at the same time. The con- 

 dition of the surface in many parts of Italy, and the an- 

 tient changes of level which it has undergone, seem 

 to bespeak the agency of this cause, if it were not 

 proved, in many other cases, by those alterations in the 

 form of the surface which have attended earthquakes. 

 The elevation of Coral islands proves that additions 

 of solid matter have been made to the strata beneath 

 them, as there is no other mode of solving this phe- 

 nomenon ; while the actual eruption of volcanoes 

 in the neighbouring parts of the ocean, leave no doubt 

 with respect to the nature of the cause. 



If, in such cases as this, we conceive the surface 

 to be removed, as it will beat some future period, 

 we should probably find many places where the ap- 

 pearances would resemble those produced by granite; 

 that is to say, masses of fused matter which have 

 not overflowed the strata. 



The next step is to apply this reasoning to the trap 

 rocks. If, in any place, the superficial masses of 

 these were to be entirely removed, we should discover 

 the openings whence they had flowed; as we have 

 already probably done, in many cases, by ascertaining 

 the places of veins. Here then we should find, what per- 

 haps we have already truly found, the unerupted trap> with 



