OF MONTE SOMMA AND VESUVIUS. 43 
It would of course be unfair to deny the possibility of such state- 
ments, but it is still more so to assert it without evidence. The error 
seems to have arisen from supposing the pumice-tufas to be older de- 
posits broken up; whereas they were new materials brought directly 
from below, as will be shown at a later stage. These light ejecta- 
menta were spread as a mantle over the flanks of the cone, but were 
afterwards transported to lower levels, rendering the upper part of 
the mountain bare, whilst the resulting alluvial deposit thickened 
around its toe. 
The true order of succession was fully recognized by Breislak and 
Von Buch at the beginning of this century, whereas inversion of 
the order is the work of recent authors *. 
Neither is there any evidence to show that the trachytic beds of 
the Campanian plain have been raised to form the basis of the 
mountain, as stated by Phillips ¢. 
Another fact of importance that will be brought out is, that the 
pumiceous deposits of the mountain are not trachytic, as generally 
supposed. 
The tufa of the Campanian plain is for the most part submarine, 
as proved by the enclosed Mollusca, and, as we have seen, of greater 
antiquity than Monte Somma. Many of the volcanos which pro- 
duced these tufaceous deposits were no doubt submarine; whilst 
others stood out at sea, as so many islands, like the present Lipari 
group. The currents of the sea that then washed the toe and inlets 
of the Apennines, swept along the ejectamenta of these eruptive 
vents, and spread out upon the sea-bottom those tufa-beds we now 
see above the surface. 
When the vent that was eventually to build up Monte Somma 
and Vesuvius burst through these earlier igneous materials, was it 
below or above the waters of the Mediterranean ? 
We have here brought before us a question that presents some 
difficulties. At Cisterna, leucitic lava of prehistoric age is quarried 
down to drainage-level, which is very slightly above that of the sea, 
for which reason the bottom of the flow has never been reached. 
When we come to consider that, from its nearness to the surface, 
this must be one of the latest streams that was poured out from 
Monte Somma, it would seem self-evident that beneath this one 
there must be many more currents which flowed into at least 
shallow water. The only other explanation that could be given 
would be gradual depression, a phenomenon quite contrary to all 
the geological evidences of the district. Breislak brings forward 
similar proofs. He mentions that in the villages of St. Elmo, 
Sirico, and Saviano, it is necessary to dig down to lava before water 
is found, and he thinks this evidence is in favour of the insular 
character of the mountain. 
We may safely suppose that the first fires of this great volcano 
were vomited into the sea, that gradually it raised its head above the 
Selo is Lobley, ‘Mount Vesuvius, with a notice of the eruption of 1868,’ 
pp. 32 and 33, also section, p. 24. 
tT Vesuvius, 1869, p. 190. 
