Phenomena in South America. 615 



that such had happened, as to have ascertained whether the next day were 

 bright or clouded. There are some active and some nearly extinct craters, 

 in the interval between the Chilian and Peruvian systems, (which is the longest 

 of any, being 900 miles,) but they are situated in countries very thinly peopled, 

 and in some parts entirely desert; and who is there in such cases to record 

 phenomena, which, even if beheld, are thought of little consequence? 



Returning to the third table, I feel no doubt that the volcanic phenomena 

 which occurred in S. America sometime previously as well as subsequently to 

 the months of January and February 1835, were far more numerous than the 

 average proportion during an equal length of time. This remark applies 

 to the two tables copied from Humboldt. In looking at the dates of these 

 events, it must be remembered that each date represents only the moment 

 when the crust of the earth has given way beneath the force, which in some 

 cases has already shown its action, and invariably continues to do so during 

 a period, often of considerable length. Under this point of view, the earth- 

 quakes of Caraccas and New Madrid, of Coseguina and Concepcion, may be 

 considered as actually contemporaneous. 



From these various circumstances, I am strongly inclined to believe, that the 

 subterranean forces manifest their action beneath a large portion of the South 

 American continent, in the same intermittent manner as, in accordance with 

 all observation, they do beneath isolated volcanos, — that is, remaining for a 

 period dormant, and then bursting forth throughout considerable districts with 



Nature of the Earthquakes on the Coasts of South America. 



I will now more particularly consider the nature of the earthquakes which 

 occur at irregular intervals on the coast of South America. It cannot be 

 otherwise than difficult to trace their precise origin, but the following con- 

 siderations, as it appears to me, lead to one conclusion alone — namely, that 

 they are caused by the interjection of liquefied rock between masses of strata. 

 UUoa, in his travels*, says, 



" Experience has sufBciently shown, especially in this country (South America), by the many 

 volcanos in the Cordillera which pass through it, that the bursting of a new burning mountain 

 causes a violent earthquake, so as totally to destroy all the towns within its reach, as happened at 

 the opening of the volcano in the desert of Carguagoazo. This tremulous motion, which we may 

 properly call an earthquake, does not so usually happen in case of a second eruption, when an 

 aperture has been before made, or, at least, the motion it causes in the earth is comparatively 

 but small." f 



* UUoa's Voyage, Vol. ii. p. 85. 



t Michell, in his remarkable paper on Earthquakes in the Philosophical Transactions for 1760, 



