48 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
information from the sections, point to one important fact. This 
evidence, compared with the results of phenomena of the same 
volcano daily passing before our observation, must make us con- 
clude that the early phenomena of Monte Somma were identical 
with those of Vesuvius at the present day, and since a.p. 1631. 
At a time, probably many centuries, before the earliest history of 
Italy commenced, Monte Somma became apparently extinct. 
It is possible that before this long but temporary extinction an 
eruption may have produced a crater of some considerable size ; but 
one is inclined to doubt it for the following reasons. At the lowest 
levels where sections exist, and where the prehistoric lavas are 
covered by loose scorize, these have always moderately fresh surfaces 
and seem to belong to permanent activity. There are no breccias 
such as would be derived from the spreading of the débris of a crater 
on the flanks of the cone. It is true that the objection may be 
raised, that such materials may have been swept away by denuda- 
tion. The loose scoria, where uncovered by lava flows, would cer- 
tainly have disappeared also, yet it presents no features of being 
disturbed in any sense. A period of inactivity must have super- 
vened, sufficiently long for the igneous magma to have entirely 
changed its character, as the subsequent pumice eruptions show. 
What was originally ejected as a highly crystalline leucitic 
basalt, principally in streams of lava, became converted into a 
vitreous paste, surcharged with water vapour, causing violent ex- 
plosions and the ejection of the igneous magma in a fragmentary 
condition. 
Puass II, ' 
That there was a period of quiescence is confirmed by a vegetable 
soil that was formed and reached some distance up the mountain. 
The scene then must have been grand—the majestic single cone with 
its purple brown slopes wreathed by a rich virgin vegetation. 
Sections showing this old plant-surface may be seen in the Vallone 
Sanseverino and the lower part of the Vallone Breislak, where we 
see at the base of the section there exposed, deposits composed of 
leucilitic scoria capped by a fine yellow dust-bed, having all the 
characters of an old vegetable soil. 
Its components are derived from the subjacent materials. The 
few lava fragments it contains are much decomposed, showing them 
to have been exposed to vicissitudes of temperature and humidity, 
such as their exposure at the surface would render them liable 
to. In this case the bed is about 40 centimetres thick. Similar 
conditions I have met with only at the lower part of the mountain 
where the inclination is slight, thus being favourable to the collec- 
tion and retention of materials suitable to the growth of plant life. 
As already said, these facts combined with other evidence point 
to a period of complete tranquillity between the last era and the new 
one that was soon to be ushered in. 
Overlying the lava, in the Vallone Pietri Pomice, are to be seen in 
section 5 metres of water-worn breccia, showing that denudation 
