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o EXPERIMEN-tS on WHINS-iONE and LAVA. 



tions of fire, may be expctflcd to afford numberlefs opportuni- 

 ties of purfuing tlie comnarifon between thefe two clalles *, 



A MOST interefling fcene for fuch a comparlfon occurs like- 

 wife on Vefuvius. The liiftory of this volcano is fimplcr than 

 that of iEtna, for it has been evidently formed, with all its ap- 

 pendages, by the continued acftion of external eruptions, which 

 have raifed it, at fome remote period, from the bottom of a fea, 

 occupying all the Campi Phlegrrci, and walhing the furround- 

 ing Appenines. The whole volcano fcems once to have con- 

 fifted of a fingle large cone, the greateft part of which has funk 

 during fome violent ei'uption, probably that which took place 

 in the time of Pliny, leaving a fragment of its bafis, now call- 

 ed the mountain of Somma. This fragment retains its original 

 fhape ; and on the fide fronting the towns of Somma and Ota- 

 jano, the external conical furface, along which the ancient lavas 

 had flowed, is flill entire. Fronting the centre of the cone, 

 Somma breaks oft" abruptly, and prefents a vertical cragg, 

 fome hundred feet in height, which is concave inwards. 

 From the gulf, produced by the ruin of the ancient moun- 

 tain, though not exadlly from its centre, have arifen the ex- 

 plofions which, by repeated accumulation, have formed the 

 prefent cone of Vefuvius. Next the fea, this cone has extend- 

 ed itfelf fo as completely to cover all remains of the ancient one, 

 forming a continued flope from the crater to the foot of the 

 mountain. On the oppofite fide it meets the bafe of the craggs 

 of Somma, and forms an angle, into which many fuccefllve 

 fl;reams of lava have flowed, producing a narrow horizontal val- 

 ley, in the form of a crefcent, called the Atrio del Cavallo. 

 From this valley the craggs of Somma prefent a complete view 

 of the internal flrudure of the ancient mountain, correfpond- 

 ing, in mofl: things, to what might have been fuppofed. 



The various fubftances, depofited fuccefllvely on the external 

 furface of the ancient cone, being cut vertically in this cragg, 



their 



» M. DoLOMiEU has obferved this diftinftion ; but fuppofes that the maffes which 

 we conceive to have flowed fubterraneoufly were erupted at the bottom of the fea. 



