Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 157 
ebullition will take place in the now relieved deep-seated magma. ‘These, in 
fact, are the conditions that prevail in what we classify as paroxysmal eruptions, 
and this is what actually happened at Vesuvius during the late eruption. 
As we proceed to examine the phenomena and the products of this last eruption, 
we shall see that the evidence they afford is that above described. 
It is probable that the cooling, crystallization, and steady increase of the 
viscosity in the lava of the chimney had gone on at such a rate that the overflow 
by the lateral outlet was insufficient to carry off this obstructing, pasty lava, and 
therefore its presence interfered with the perfect freedom of vapour escape from 
lower down. The result of this would be a disruptive tendency, which resulted in 
the formation or reopening of a number of radial fissures, splitting the cone in 
different azimuths, and as viscous lava filled these, fresh, more gas-bearing magma 
rose, ebullition went on more actively, representing the increased activity of the 
earlier days of the eruption. These lateral openings at a relatively low level 
were so efficient in giving exit to the upper portion of the obstructing lava that 
this was rather suddenly removed, so that at the climax of the eruption deep- 
seated, more aquiferous magma, now relieved of its overlying burden, rose in 
the chimney, and was, in consequence of the rapid and violent ebullition of 
effervescence, projected to great heights, as the blackish-brown or lighter vesicular 
scoria, or essential ejecta that was scattered over the flanks of the mountain in 
the earlier hours of April the 8th. This was followed by magma coming 
from still greater depths, having acquired less water, and consequently being 
richer in heat-energy at its eruption. This magma is denser and more micro- 
crystalline in consequence of slower cooling. This constitutes the second 
stratum of black scoria scattered around the mountain, and especially over 
Ottajano and neighbourhood in the early morning. Just as in a bottle of 
champagne newly opened, when the first frothing-up has subsided, so mn the 
morning of the 8th the ebullition of the magma could no longer reach the crater- 
edge, the ‘fountain of fire” was replaced by the ‘fountain of stones.” The 
crater-edges having no support were now more extensively torn and pared away 
by the vast amounts of gases still escaping, which projected the resulting materials 
high into the atmosphere from which they fell, and constituted the third and major 
part of the breccia and lapilli stratum, such as we see especially in the north-east 
section of the voleano. This represents the eruptive period from the morning to 
the evening of April 8th. Not only did the escaping gases pare, excavate, and 
tear away the walls of the chimney, converting it into the fine crater we now see, 
but slips of the tuff and ash along its edges precipitated the materials down the 
chimney, in face of the uprushing vapour which projected them many kilometres 
into the atmosphere. 
Most of these materials have been subjected, between the time of their 
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