Phenomena in South America. 623 



energ-y. According- to M. Boussingault*, those earthquakes in South America 

 which have been most destructive to human life^ that is^ which have been most 

 sudden and violent, have not coincided with volcanic eruptions. He adduces 

 several instances, including the shocks felt at Caraccas in 1812; but, according- 

 to Humboldtf , the connexion between the subterranean disturbances at that 

 place and the West Indian vents can hardly be doubted. M. Boussingault's 

 remark, indeed, although perhaps generally true, should be taken with some 

 reserve; for had the earthquake of Concepcion happened at night, thousands of 

 persons must inevitably have perished. 



In a line of fracture, produced by subsidence, the distortion and overthrow of 

 the strata would probably be even greater than in one of elevation, from the cir- 

 cumstance, that as soon as the weight of the mass overcame its cohesion, and it 

 began to sink, there would be no counterbalancing power, like gravity during 

 elevation, to check the movement, excepting, indeed, the lateral pressure of the 

 masses together, and this would only add to the disturbance. There would be, in 

 this case, no axis of injected plutonic rock, or at least not one protuberant above 

 the general surface; and thus we may explain the extreme disturbance in the 

 strata of countries which are only hilly, like parts of Great Britain ; and the oc- 

 currence there of such axes of elevation, as they are generally called, but which 

 probably, in most cases, would be more appropriately termed axes of subsidence. 



If the theory which I have given of the cause of the earthquakes on the 

 west coast of South America be true, we might naturally expect on the same 

 principle to find proofs of successive formation in the many parallel ridges, of 

 which the Cordillera is composed. In the parts of Central Chile which I 

 examined, this is true, even with regard to the two main lines ; of which one 

 is partly formed of inclined beds of conglomerate, consisting of pebbles de- 

 rived from the rocks of the other. I have also evidence, but of a less satis- 

 factory kind, that some of the exterior lines of mountains are altogether of 

 subsequent date to the more central ridges. Moreover, in all parts of the 

 Cordillera, there are proofs of an equable elevation in mass to a very great 

 altitude. I was so much struck with this latter fact, connected with what I 

 imagined must have taken place during the Concepcion earthquake, that I 

 came to nearly the same conclusion, which Mr. Hopkins has demonstrated by 

 his mathematical researches, namely, that mountain-chains are only subsidiary 

 and attendant phenomena on continental elevations. If this be so, and few, 

 after having read Mr. Hopkins's memoir, will dispute it; then, as it is certain 

 continental elevations have certainly taken place on a great scale within the 



* Bulletin de la Soc. Geo!., Vol. vi. p. 54. 



f Personal Narrative, Vol. ii. p. 226, and Vol. iv. p. 6, English Translation. 



