OF SOMMA MONTE AND VESUVIUS. 89 
but one outlet, probably the Fosse’ Vetrana and Faraone. It is 
only in this manner that we can reconcile the two descriptions. 
According to the opinions of Prof. Palmieri* the Plinian erup- 
tion played a most important part in the building up of the modern 
Vesuvian cone. It is a remarkable fact that very rarely does 
a paroxysmal eruption terminate in a cone-forming stage, but 
rather leaves a jagged crater whose sides gradually shelve down 
to the chimney or vent. Even admitting a cone of considerable 
size to have been formed, we shall see that subsequent eruptions, 
and especially that of the fifth century, must have inevitably 
destroyed it. 
This eruption seems to have followed the usual course. It com- 
menced by the sudden explosion and frothing up of the vitreous 
amphibole-bearing magma. When the tension had been somewhat 
relieved, the ejection became more regular, and took a longer time to 
expel a given quantity of material, so that this could undergo a cer- 
tain amount of crystallization, thus permitting the replacement to a 
considerable extent of the vitreous base by a microcrystalline one, 
and increasing the size of the already existing crystals, besides 
adding pyroxene j to its microliths. 
The diminution of force would go on until the pumice and other 
material would no longer reach the outer slopes of the crater, but 
would undergo mechanical disintegration by the continual motion to 
which they would be subjected by the comparatively feeble eruptive 
action going on in that space. The breaking up of the pumice 
would be aided by the feebler cohesion among the microliths than 
between the molecules of the more vitreous examples. ‘The re- 
sulting fine ash would be carried by the uprushing column of vapour, 
to be borne away and deposited as the pisolitic bed. This seems to 
have fallen as, or soon to haye been converted into, a mud by the 
mingling with the condensed vapour and pulverized water derived from 
the inflow into the crater and chimney. That this material was a 
mud when it first reached its present site seems proved by the 
accurate moulds it took of men and animals before any decom- 
position had set in. In fact it appears from the Plinian epistle 
that it was probably this fine material that had such a fatal effect 
upon the elder Pliny. He was, one would imagine, from the descrip- 
tion of him, rather a stout man, whose respiratory and circulatory 
organs had undergone considerable senile degeneration, so as to be 
unable to resist what his attendants escaped from. 
It has not been considered worth while to go into the long con- 
* «Vesuvio e la sua Storia’ and ‘ Pompei e la regione sotterata dal Vesuvio 
nell’ anno Lxx1x.’ Napoli, 1879, p. 94. 
t This goes to confirm what has been said of the relation between these two 
allied minerals and the pressure under which they were formed. That they 
depend upon the different conditions under which they were brought into ex- 
istence, and the difficulty of the crystallization of amphibole at ordinary pressure, 
seems well shown by the following experiment: “ Nous avons encore produit 
une andésite augitique en fondant un mélange de 10 parties d’oligoclase et 
dune partie d’amphibole ; l’amphibole s‘est done transformée en pyroxéne.” 
Fouqué et Levy, ‘Synthése des minéraux et des roches,’ p. 60. 
