Phenomena in South America. 609 



In a geological point of view, it is of the highest importance thus to find 

 three great phenomena, — a submarine outburst, a period of renewed activity 

 through many habitual vents, and a permanent elevation of the land, — forming 

 parts of one action, and being the eifects of one great cause, modified only by 

 local circumstances. When w,e consider, that the southern volcanos were in 

 eruption some days before the earthquake, and that one of them, Minchinma- 

 dom, has seldom been dormant for the last thirty years, and that they all re- 

 mained active for many months afterwards, we must conclude that the impulse 

 given to them at that moment, was of the same nature with the force wliich 

 has kept up their activity during the many ages necessary to accumulate the 

 volcanic matter into great snow-clad cones, and which force still continues to 

 add to their height. If the earthquake or trembling of the ground (which, 

 however, we have seen was less near these volcanos than elsewhere) had 

 acted in no other way, than in merely breaking the crust over the lava within 

 the craters, a few jets of smoke might have been emitted, but it could not have 

 given rise to a prolonged and vigorous period of activity. 



But the power which manifested itself in this renewed action, and to which 

 same power, acting at former periods, the entire formation of these several 

 volcanos has evidently been due, was likewise the cause of the permanent 

 elevation of the land ; — a power, I may remark, which acts in paroxysmal up- 

 heavals like that of Concepcion, and in great volcanic eruptions, in precisely 

 the same manner, for both these phenomena occur only after long intervals 

 of rest, during which the volcano merely casts out, perhaps, a few showers 

 of scoriae, and the land rises with so slow a movement that it is called insen- 

 sible ; — therefore no theory of the cause of volcanos which is not applicable 

 to continental elevations can be considered as well-grounded. Those who 

 believe that volcanos are caused by the percolation of water to the metallic 

 bases of the earth, or simply to intensely heated rock, must be prepared 

 either to give up this view, or to extend it* to the elevation of such vast con- 

 tinents as that of South America. 



* The arguments in favour of the theory, that steam, produced by the percolation of water to the 

 interior of the coohng planet, is the motive power in volcanic action, has been lately strongly put 

 by Prof. Bischoff in his paper in the Edinburgh Journal (Vol. xxvi. p. 25.). That it must be a 

 modifying cause of great importance seems highly probable; but that it is the primary one of con- 

 tinental elevations, I cannot admit. The phenomenon, as it appears to me, is on far too grand a 

 scale to harmonize with such an explanation. Can the rising of the whole west coast of South 

 America, and of the whole width, at least of the southern portion of it, be explained by the lateral 

 force exerted during the general shrinking of the earth's crust, modified only by the formation of 

 steam under high pressure, in those parts where water has percolated to the heated interior 1 Such 

 an explanation surely is inadmissible. 



