176 _ Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 
mountain was viewed from the south between Torre del Greco and Torre 
Annunziata (fig. 10, Pl. X.). On approaching and inspecting the great cone from 
the Pedimentina, the Atrio del’ Cavallo, or the ridge of Somma, one was impressed 
by the relative smoothness of its surface. ‘This was due to the practical absence 
of any water-erosion on the extremely permeable coarse lapilli, scoriz, or thin 
scoriaceous lava-surfaces that clothed it, and any gutter or irregularities of it 
were soon obliterated by the shifting, unstable nature of its covering, so that 
depressions were rapidly filled up, preventing water from collecting in mass. 
The principal cause of its smoothness was, however, the absence for many 
years of any important fall of fine dust in sufficient quantities to make an 
impermeable surface upon which water could be collected, in sufficient volume, 
and be shed so as to produce erosive action. 
When the huge, sombre dust-screen disappeared after the eruption, the 
remains of the great cone offered to the eye a view of its slopes deeply scored 
by a series of remarkable symmetrically arranged darancos of no mean dimensions, 
extending radially from the crater-edge (Pl. V.). The first explanation that 
suggested itself was water as the sculptor of these; but when it was known that 
only relatively insignificant showers had fallen during and immediately after the 
eruption, it was patent that other causes had been at work. 
On my arrival at Naples, late in April, as I watched the cone day by day, 
I was struck by the almost continuous slips that were taking place on its flanks; 
and by carefully watching them, it could be seen that these masses of loose 
material were practically identical with snow-avalanches. I attempted to 
photograph some of these; but unfortunately the negatives turned out un- 
satisfactory. Two photographs, however, were more successful—by M. F. A. 
Peret and M. A. Brun—one of which I am able to produce here by the courtesy 
of the artist (Pl. XIX.). 
The new crater-forming stage started on the 4th of April. As the magma 
sank in the chimney, in consequence of the new drain opened to the south, the 
ejection of essential materials, as lava-cakes in the cone-forming stage, gradually 
ceased, and during the afternoon were mostly replaced by the accessory materials 
derived from the now unsupported chimney-walls. During the next three days 
a thick layer of the debris of the now rapidly growing crater was spread over 
the slopes of the great cone and its immediate neighbourhood. During the great 
output of fragmentary materials from the 7th to the 9th vast quantities must have 
been spread as a heavy mantle on the cone, and, no doubt, a good deal of slipping 
then occurred. During the very violent propulsion of the fragmentary debris of 
the rapidly growing crater, much of it reached beyond the slopes of the cone. 
Later, as the ballistic energy of the volcano diminished, and as materials had to 
be hoisted from greater and greater depths, as the crater-apex was lowered, the 
