4G2 
SIMULTANEOUS ACTION. 
Azores, of the Caribbee islands of Mexico, of Guatimala, 
and of the table-land of Quito ; when we examine either the 
reactions of these different systems of volcanos on one 
another, or the distance at which, by subterranean commu- 
nication, they simultaneously convulse the earth. 
The study of volcanos may be divided into two distinct 
branches ; one, simply min era! ogi cal, is directed to the exa- 
mination of the stony strata, altered or produced by the 
action of lire ; from the formation of the trachytes or trap- 
porphyries, of basalts, phonolites, and dolerites, to the most 
recent lavas: the other branch, less accessible and more 
neglected, comprehends the physical relations which link 
volcanos together, the influence of one volcanic system on 
another, the connection existing between the action of 
burning mountains and the commotions which agitate the 
earth at great distances, and during long intervals, iu the 
same direction. This study cannot progress till the various 
epochs of simultaneous action, the direction, the extent, and 
the force of the convulsions are carefully noted ; till we have 
attentively observed their progressive advance to regions 
which they had not previously reached ; and the coincidence 
between distant volcanic eruptions and those noises which 
the inhabitants of the Andes very expressively term subter- 
raneous thunders, or roarings.® All these objects are com- 
prehended in the domain of the history of nature. 
Though the narrow circle within which all certain tradi- 
tions arc confined, docs not present any of those general 
revolutions which have heaved up the Cordilleras and buried 
myriads of pelagian animals ; yet Nature, acting under our 
eyes, nevertheless exhibits violent though partial changes, 
the study of which may thrgw light on the most remote 
epochs. In the interior of the earth those mysterious powers 
exist, the effects of which are manifested at the surface by 
the production of vapours, of incandescent scoriae, of new 
volcanic rocks and thermal springs, by the appearance of 
Cotopaxi, Tnngnragun, Pichinclia, Antisana, and Smigai, belong to the 
same system of burning volcanos ; they are generally ranged in rows, as 
if they had issued from a crevice, or vein not fdled up: and, it is very 
remarkable, that their position is in some parts in the general direction of 
the Cordilleras, and in others in a contrary direction. 
* Bramidos y truenos subterraneos. 
