Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 179 
in November, when I examined the locality. It was steadily extending upwards, 
and would soon reach the edge of the crater, so that in future the cone will here 
possess a marked depression, and consequent weakness, in the direction favour- 
able for future outbursts. No doubt, the number of new dykes will tend to knit 
the cone together in that direction, which will in some way compensate for the 
loss of material on the south side. 
The angle between the Pedimentina and the cone on the south was a fairly 
sharp one before the eruption; but the vast amount of material of the slips has 
filled it up, so that it is almost impossible to draw a line between cone and 
Pedimentina. 
Before the eruption the Colle Margherita stood out as a distinctive feature 
in the Atrio del Cavallo; in fact, it formed a third though smaller prominence 
between the summits of Somma and Vesuvius. Between the cone and the apex 
of the Colle Margherita there was a distinct notch. Since the eruption that 
notch has been filled in, so that one walks almost on a level from the slope of 
the cone along a blunt ridge or saddle to the summit of the Colle Margherita. 
The cone, before the eruption, was a fairly symmetrical one, even at its 
summit. The constant activity of Vesuvius from 1876 had steadily filled up and 
healed, as it were, the crater of 1872, and had piled up on the materials filling 
that crater other lavas and scoriz, so that the apex of the eruptive cone, 
although somewhat blunt, formed a fairly harmonious curve with the sloping 
sides of the great cone of Vesuvius. 
The exact altitude of the cone during the days preceding the eruption is rather 
difficult to fix, as it varies from day to day. Calculating from A. Fiechter’s 
data* and the new map issued by the Istituto Geografico Militare, the result of 
their survey, the height works out at 1323m. or 1330m. Mercallit gives it at 
1335 m., and De Lorenzof puts it at 1321m. Taking the average of these four, 
we get in round numbers 1327 m. 
In October, 1903, I fortunately took a panoramic view of Vesuvius from the 
Punta del Nasone; and on May 4th, 1906, just after the eruption, again made 
another photograph with the same lens and camera, and from the same spot. The 
latter photograph is reproduced in Pl. III. I have added the outline of the 1903 
photograph, which gives an exceedingly clear, graphic conception of the great 
changes in the shape of Vesuvius. The first point that strikes us is the removal of 
about one-third of the original cone by the formation of a large crater. I say large, 
as compared with those usually produced by paroxysmal outbursts at Vesuvius; 
but really very small if we compare it with that of the ancient explosive eruptions 
of Monte Somma, represented in the same photograph as encircling the whole cone 
* Op. cit., Boll. Soc. Geol. Ital., vol. xxv., p. 846. tp Ope c2t.sape Lila 
{ Quart. Journ. Geol. Soc., vol. Ixii., p. 481. 
TRANS. ROY. DUB. SOC., VOL. IX., PART VIII, 2 F 
