Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 148 
at the summit of the mountain, which, with variations, continued till the 27th of 
May, 1905, when two new mouths opened a short distance down the north-west 
side of the cone, close to the rifts of 1895 and 1903, and possibly may be but 
a reopening of one of the same old radial dykes. Strangely, though with a 
difference of altitude of 65 m., lava constantly dribbled from these two mouths 
for ten months, while the main volcanic chimney continued to show that range of 
variations that is so characteristic of Vesuvius in its more recent history. These 
variations at the rent have been described by Professors Mercalli and Lacroix as 
Strombolian and Vulcanian stages. My old definitions of cone-forming, or crater- 
forming, stages seem to me to be more precise. ‘The analogy of Vesuvius with 
Vulcano is most unsatisfactory, the chemical nature, viscosity, and other physical 
characters of their magmas being so widely different as to make such a comparison 
most misleading. 
I have given here a succinct account of the principal changes in the great 
Neapolitan volcano from its last paroxysm in 1872 down to the one I propose to 
describe. It would have been out of place here to enter into the more minute 
details, which can be gleaned from the writings of Scacchi, Palmieri, and Diego 
Franco, from 1872 to 1879, my own records published from 1879 to 1894, and 
since then those of Professors Matteucci and Mercalli. 
Certain general principles, however, are, I think, to be drawn from this period 
in the history of Vesuvius, which the above-mentioned authors do not seem to 
have entirely appreciated. No less than five great solid masses of lava were 
added to the volcano; and, were it possible with any accuracy to estimate the 
ageregate volume of these, we might form some conception of the very considerable 
increase in the total bulk of the mountain. We might even hazard an estimate of 
the actual time taken to build up the whole of that striking feature of the Gulf of . 
Naples—the type-volcano of the world. 
These five great bosses grouped about the main cone, composed, as they are, 
of lava, with practically no fragmentary material, must constitute points of 
resistance to later outbursts near their sites. In fact, I have given a general 
description of these bosses and buttresses, as, where they existed in any great 
thickness, they certainly seem to have prevented the radial dykes of the 1896 
eruption from reaching the surface; but I feel inclined to believe that for a 
considerable time in the future history of Vesuvius we shall see their tectonic 
influence. A fact they unquestionably show is that, at any rate so far as the 1883 
and 1885 outpours are concerned, vast coherent lava-masses can consolidate on 
steep slopes and add to the building of a cone, provided the outflow is sufficiently 
slow and continuous. 
