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(TS 



Ch. XXVI.] 



ITS GEEAT ANTIQUITY. 



45 



of annual growth, and observed what thickness the tree 

 had gained in that period. The average rate of growth of 

 younger trees, of the same species, was then ascertained, and 

 the calculation made according to a supposed mean rate of 

 increase. De CandoUe considers it not improbable that the 

 celebrated Taxodium of Chapultepec, in Mexico {Cuj)ressus 



distkJm Lmn.), which is 117 feet in circumference, may be 

 more aged. 



It is, however, impossible, until more data are collected 

 respecting the average intensity of the volcanic action, to 

 make anything like an approximation to the age of a cone 

 like Etna ; because, in this case, each successive envelope of 

 lava and scorise is not of simultaneous grow^th round the 

 mountain, like the layers of wood round a tree, and therefore 

 affords us no corresponding and definite measure of time. 

 Each conical envelope is made up of a great number of dis- 

 tinct lava currents and showers of sand and scoriee differino- 



in width and depth, and also the results of intermittent 

 action exceedingly variable as to intensity and frequency of 

 recurrence. Yet we cannot fail to form the most exalted 

 conception of the antiquity of this mountain, when we con- 

 sider that its base is about 90 miles in circumference ; so 

 that it would require 90 flows of lava, each a mile in 

 breadth at their termination, to raise the present foot of the 

 volcano as much as the average height of one lava current. 



The injection of several thousand dikes into the mass of 

 matter previously accumulated, is more comparable, as M. E. 

 de Beaumont has hinted, to the endogenous growth of a tree 

 implying the stretching outwards and perhaps upwards also 

 of the mountain. But observations within the historical era 

 are too imperfect to enable us to decide whether the moun- 

 tain has gained or lost in altitude at those periods' when new 

 fissures have been formed and filled. 



most conspicuous minor 



Monti 



produced within the times of authentic history. Even this 

 hiU, thrown up in the year 1669, although 450 feet in height, 

 only ranks as a cone 

 near Bronte, rises. 



Monte Minardo 



even now, to the height of 750 feet. 



