657 



being the effects of one great cause, modified only by local circum- 

 stances. Mr. Darwin further observed, that, as the volcanos near 

 Chiloe commenced, at the moment of the shock, a period of renewed 

 activity, which lasted throughout the following year, the motive 

 power of these volcanos (as well as of the submarine outburst near 

 Juan Fernandez) must be of a similar nature with that, which, at the 

 same instant, permanently raised another part of the coast ; and he 

 therefore concluded, that no theory of the cause of volcanos, which 

 is not applicable to continental elevations, can be considered as well- 

 grounded. 



Mr. Darwin then offered some remarks on the two tables pub- 

 lished by Humboldt, of the great earthquakes which affected, in 1797 

 and 1811, so large portions of America ; and he is of opinion, that a 

 repetition of the coincidences can alone determine how far the in- 

 creased activity of the subterranean powers, at such remote points, 

 was the effect of some general law, or of accident. He likewise dis- 

 believes that periodical eruptions, as those of Coseguina, in 1709 and 

 1809, or of earthquakes, as the shocks felt at Lima on the 17th of 

 June 1578, and the 17th of June 1678, are more than accidental 

 agreements. He also gave a table of the volcanic phsenomena in 

 South America in 1835 ; and concluded, that it is probable that the 

 subterranean forces manifest, for a period, tlieir action, beneath a 

 large portion of the South American continent, in the same inter- 

 mittent manner as they do beneath isolated volcanos. In the latter 

 table, Mr. Darwin pointed out the case of Osorno, Aconcagua, and 

 Coseguina, (the first and last being 2700 miles apart,) which burst 

 into sudden activity early on the morning of June 20th, 1835 ; but he 

 hesitated to assent to there being any necessary connexion between 

 them. He further remarked, that if such simultaneous outbursts 

 had been observed in Hecla and ^tna, points unconnected by any 

 uniformity of physical structure, it would be doubtful how far they 

 would have been worthy of consideration ; but in South America, 

 where the volcanic orifices fall on one line of uniform, physical struc- 

 ture, and where the whole country presents proofs of the action of 

 subterranean forces, he conceives it ceases to be improbable, to any 

 excessive degree, that the action of the volcanos should sometimes 

 be absolutely simultaneous. 



The author then briefly described the groups into which the vol- 

 canic vents of the Cordilleras have been divided. The most south- 

 ern extends from Yntales to the volcanos of central Chili, a dis- 

 tance of nearly 800 geographical miles ; the second, from Arequipa 

 to Patas, rather more than 600 miles ; the third, from Riobamba to 

 Popayan, a distance of about 300 miles ; and to the northward, 

 there are in Guatimala, Mexico, and Cahfornia, three groups of vol- 

 canos separated from each other a few hundred miles. That the 

 vents ill each of these groups are connected, the author has little 

 doubt ; but that the groups are united in one system, there are less 

 satisfactory means of proving. 



Mr. Darwin next considered the nature of the earthquakes which 

 occur at irregular intervals on the South American coast. He is 



