OF MONTE SOMMA AND VESUVIUS. 85 
all the ‘‘ formed ” materials seem to have collected around the leucites 
as so many nuclei, which in any but thin sections iook like a great 
number of granular brown bails, crowding one upon another. ‘The 
vesicuiarity of the rock is slight, and the cavities, instead of having 
sweeping outlines, as in the vitreous pumice, are irregular, having to 
find a place between the leucite and its attendent microliths. In 
neither of these subdivisions does the leucite attain any considerable 
size. As already pointed out, these are but artificial subdivisions ; 
just as in other cases, there is not any distinct line of demarca- 
tion between them. ‘The upper portion, both to the naked eye and 
in microscopical structure, is a more highly crystalline condition 
of the lower. 
Superposed in a very abrupt manner upon this thick deposit of 
pumice is a fine brownish or greyish ash-bed, which forms the 
third subdivision. 
General Description.—lt is remarkable for its great richness in 
pisolites, which are well formed and may reach one or two centimetres 
indiameter. ‘This pisolitic bed is broken by two thin bands of lapilli, 
the lower one only separated by a few centimetres from the surface 
of the pumice, whereas the upper seems to be the last product of 
the eruption or at least nearly so. The lapilli seem to be of leucilitic 
lava, mixed with a few fragments of highly microlithic pumice. 
This ash-bed, if we may call it so, taken as a whole, is moderately 
coherent, and must have either been deposited in a moist condition, 
or have assumed that form very quickly. This is proved by the corpses 
of some of the fleeing Pompeians which were enveloped in it, which, 
although they have completely disappeared, have left a perfect 
hollow mould. Signor Fiorelli has on many occasions been able to 
reproduce the forms by pouring liquid plaster of Paris into the 
hollow. The casts prove that the originals were enveloped suddenly ; 
for there are no signs of gaseous distension of the abdomen, Syl 
soon results from decomposition. 
the panies that occurred from time to time in the eruptive pheno- 
mena. ‘Thus Pliny says, ‘“ It [the cloud] appeared sometimes bright, 
and sometimes dark and spotted, as it was more or less impregnated 
with earth and cinders.” ‘* He was now so nigh the mountain that 
the cinders, which grew thicker and hotter the nearer he approached, 
fell into the ships, together with pumice stones and black pieces of 
burning rock.” ‘ They consulted together whether it would be most 
prudent to trust to the houses, which now shook from side to side 
with frequent and violent concussions, or to fly to the open fields, 
where the calcined stones and cinders, though light, indeed, yet fell 
in large showers and threatened destruction.” These quotations from 
the first epistle show that the earlier part of the eruption consisted 
of ejection of pumice, stones, &c. (2. e. ejected foreign rocks, and 
leucilitic lapilli) ; ‘‘ black pieces of burning rock” also probably refer 
to these latter materials. 
In the second epistle we read this: ‘Soon afterwards [first or 
second morning after the departure of the elder Pliny ?} the cloud 
