Phenomena in South America. 631 



quake of February 20th, 1835, passed over Valdivia, but affected the districts 

 north and south of it; and it appears that this town, until November 1837, had 

 been less injured by the innumerable shocks which devastated Chile than any 

 other ; yet the subterranean abysses directly beneath it are in connexion (as 

 shown by the action of Villarica in 1822) with the district to the North, 

 which has been so often convulsed ; and in November 1837, at the same 

 time that an island far southward was upraised eight feet, it was shaken by 

 an earthquake so violent that it escaped utter ruin only from the houses being- 

 built of wood. The comparative freedom from disturbance of Valdivia on the 

 20th of February, cannot be attributed to the action of Villarica, for we have 

 seen that this volcano was quiet ; nor indeed is there any reason why such an 

 effect should be attributed to its action, since the eruptions of Osorno and 

 Minchinmadom did not save the northern parts of Chiloe, though they occupy 

 the same relative situation with regard to them, which Valdivia does to Villarica. 

 Shall we then say, that Valdivia escaped so long the subterranean disturbances, 

 some of which affected simultaneously regions north and south of it, solely 

 on account of the greater strength of the crust in that part ? This appears 

 to me a cause quite inadequate ; and the direct supposition is better, that as 

 within the same period one part of the continent has been elevated more than 

 another, so the lava has been propelled by the action of this force more pow- 

 erfully towards some, than towards others, of the volcanic orifices which 

 penetrate it. 



The secular shrinking of the earth's crust has been considered by many 

 geologists a sufficient cause to account for the primary motive power of these 

 subterranean disturbances ; but how it can explain the slow elevation, not only 

 of linear spaces, but of great continents, I cannot understand. With the same 

 view, some highly important speculations have recently been advanced, — such 

 as changes of pressure on the internal fluid mass, from the deposition of fresh 

 sedimentary beds, and even the attraction of the planetary bodies on a sphere 

 not solid throughout; but we can see that there must be many agents, modi- 

 fying all such primary powers ; and the furthest generalization, which the 

 consideration of the volcanic phenomena described in this paper appears to 

 lead to, is, that the configuration of the fluid surface of the earth's nucleus is 

 subject to some change, — its cause completely unknown, — its action slow, in- 

 termittent, but irresistible. 



