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ob. xxv;] 



ORIGIN OF THE CONE OF VESUVIUS 



63] 



modern Vesuvius have poured ; the axis of the present cone 

 f Vesuvius being, according to Visconti, precisely equidistant 

 f ro m the escarpment of Somma and the Pedamentina. 

 In the same diagram I have represented the slanting beds 



Fig. 67. 



Supposed section of Vesuvius and Somma. 



a. Monte Somma, or the remains of the ancient cone of Vesuvius. 



b. The Pedamentina, a terrace-like projection, encircling the base of the recent 



cone of Vesuvius on the south side. 



c. Atrio del Cavallo.* 



d, e. Crater left by eruption of 1822. 



/. Small cone thrown up in 1828, at the bottom of the great crater. 

 fj, g. Dikes intersecting Somma. 

 h, h. Dikes intersecting the recent cone of Vesuvius. 



N.B. The inclination of the beds at a, e, f, d, is considerably exaggerated in this 

 diagram for want of more space. 



of the cone of Vesuvius as becoming: horizontal in the Atrio 

 del Cavallo at (c), where the base of the new cone meets the 

 precipitous escarpment of Somma ; for when the lava flows 

 down to this point, as happened in 1822, its descending course 

 is arrested, and it then runs in another direction along this 

 small valley, circling round the base of the cone. Sand and 

 scoriae, also, blown by the winds, collect at the base of the 

 cone, and are then swept away by torrents ; so that there is 

 always here a flattish plain, as represented. In the same 

 manner, the small interior cone (/) must be composed of 

 sloping beds, terminating in a horizontal plain ; for, while 

 this monticule was gradually gaining height by successive 



* So called from travellers leaving their horses and mules there when they 

 prepare to ascend the cone on foot. 



