40- 



ETNA. 



[Ch. XXVI. 



claj, at tlie height of 1,000 or 1,200 feet above the sea 

 washing out of it fossil shells of living species strong enoudi 

 to bear transportation as far as Riposto. 



>/ 



The action of volcanos is, as 



have already seen, characteristically intermittent even when 

 they are in a phase of frequent eruption ; but we have good 

 reason to believe that if their history could be known for 

 thousands of years, we should find that there are very lono- 



dormant 



'om 



cones of Java it appears that these volcanos are subject to 

 protracted periods of inaction, during which valleys, deepen- 

 ing as they descend, are eroded by running water on all their 

 sides ; at length a paroxysmal outburst occurs, by which part 

 of the cone is destroyed, and then lavas again pour out from 



time. Mr 



com 



of the periods during which any one of them has been at 



rest 



estimated 



r 



which furrow their sides ; but the time which such denuda- 

 tion may have occupied has often been so vast that we cannot 

 attempt, with our present knowledge, to form any conjecture 

 as to its duration. 



From what was said of Vesuvius in the last chapter, the 

 reader is aware that until the year 79 of our era, it had 

 P.11 the characters of an extinct volcano. The only part of 

 the exterior of the ancient cone which still retains that 

 physiognomy by which the whole of it must have been cha- 

 racterised before the renewal of its volcanic activity, is tlie 

 northern side, scarcely ever visited by travellers, and which 

 we have described as being intersected by numerous deep 

 ravines, radiating as from a central axis towards all points of 

 the compass. On ascending several of these ravines, we have 

 seen that they terminate abruptly in perpendicular precipices 



60 to 300 feet in height, where in the rainy season 

 there are waterfalls.^ Above the head of such precipices 

 shallow valleys continue upwards to the crest of the boundary 

 wall of the Atrio del Cavallo, and no doubt were once con- 



* Sec Vol. I. p. 634. 



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