OF MONTE SOMMA AND VESUVIUS. 101 
The histology of the component minerals and the mass itself seems 
to point to a somewhat feeble paroxysmal eruption, that is to say, one 
in which the ejection was sufficiently slow to allow of the great deve- 
lopment of the formed matter. Yet at the same time we must re- 
member that it was violent enough to tear out a large cavity deep 
enough to reach the underlying limestone of the volcanic floor. 
There is little doubt that a considerable part of the cone that had 
been built up by former eruptions must have been gutted, leaving a 
craterial hollow in the great crater-plain, so as to form a terraced 
depression. 
To what date does this eruption belong ? 
In the year 1036 occurred one of the historic eruptions of this 
famous volcano, but as large streams of lava are said to have flowed 
down the sides of the mountain, this would not suit the character of 
the ejectamenta. These may therefore be, in all probability, referred 
to one of the two eruptions said to have occurred in the years A.D. 685 
and 993, but of which we have no details. 
This is the last deposit that has, so far, been discovered of which 
there is any possibility of determining the date, except the modern 
lava-flows, or of any ejectamenta that have the pumiceous type of 
structure. 
All these beds we have been describing are at various points 
overlain by dense scoria, lapilli, and lavas undistinguishable from the 
products that are at present constantly ejected from Vesuvius. 
All the eruptions, 1036-1038, 1049, 1138-1139, 1806, 1500, 
1568, from what we know of them, seem to have been semi- or non- 
paroxysmal in type. It appears that, with the exception of one or two, 
no lava is mentioned as being derived from them. This hardly ex- 
cludes the overflow of lava; and we must rather regard it as finding 
its way into the atrio, and filling up the space around the base of 
the cone of eruption within the great crater-wall. At the same 
time the cone of eruption increased, and was raised by the direct 
deposition of new ejectamenta upon its outer surface, or was from 
time to time gutted, having its interior broken up to form a crater, 
the materials being spread over its slopes. 
From the description of Sorrentino, it appears that, before the 
eruption of 1631, in descending into the great crater one arrived 
at a plain; then, after traversing woods, another craterial hollow 
was seen, the bottom of which was occupied by some warm lakes. 
The great eruption of 1631 may be looked upon as the first of 
that wavering but continuous action that has continued uninter- 
ruptedly to the present time, and which seems to be identical in 
character with that permanent activity which gave birth to the 
earliest lavas we know as issuing from this volcano. 
Overlying the deposits of Puasr VI., Period 4, often inseparable 
from, or appearing to be continuous with, the pisolitic bed, comes a 
series of materials that may even reach 80 metres in thickness. 
They are seen in greatest abundance around the foot of the moun- 
tain, and rarely extend in any thickness above and beyond the 
junctions of a lagno and vallone. 
