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Cir. XXV.] 



TO MONTE SOMMA OR TO VESUVIUS. 



637 



remote period and then imbedded in the old tuffs like pieces of 

 dolomite and other rocks foreign to the mountain. They only 

 prove that some of the early eruptions burst through tuffs 

 of marine origin like those found between Naples and Vesu- 

 vius. Such tuffs contain similar shells, but seem only to rise 

 to the height of about thirty feet above the level of the sea. 



As to the sea-shells said to have been found on the north 

 side of Somma, I learned that the guides, finding such fossils 

 to be in request, have been in the habit of taking from the 

 sea-shore fragments of tuff covered with the recent Vermetus 

 and passing them off as fossils belonging to ancient and 



Somma 



There is nothing in 



imensions 



opposed to the notion of its having originated from the same 

 central axis of eruption as that by which the modern Yesu- 

 vius has been formed. I observed in 1857 that the top of 

 the escarpment where it lowers towards Ottajano, as well as 

 the flank of the old mountain below, was almost entirely 

 devoid of vegetation, from the sterilising effect of the volcanic 

 sand and rapilli which fell upon it during the eruption of 



more 



om 



r» 



the crater. I found in it some of those pear- 

 shaped masses of scoriae called volcanic bombs, also projected 

 from the crater in 1822. This circumstance, together with 

 the fact that the opposite side of Vesuvius was in like man- 

 ner reached to an equal distance from the present centre of 

 eruption by the matter then ejected, is a clear proof that we 

 want no greater power than that possessed by the existing 

 volcanos to reconstruct a cone having as large a diameter as 

 Somma. No upheaval is wanted to perform such a feat, the 

 ordinary forces of the elastic vapours being amply sufficient. 

 The ravines then on the north side of Somma demonstrate 

 that the origin of that mountain was due to successive 

 flows of lava and showers of scoriae, and that there were many 

 long intervals of rest between successive eruptions, during 

 which valleys of aqueous erosion were scooped out, and 

 forest-trees and shrubs had time to grow. These plants 

 were sometimes buried in showers of pumiceous matter, or 

 m mud sweeping down the steep slopes. But how, it will be 



