186 Jounston-Lavis—The Lruption of Vesuvius in April, 1906. 
The average slope of the old cone was 27°, and represented the angle of at 
least the middle two quarters, the lower and upper quarters being less. Now, the 
upper half has about that angle, but the lower half has an average of 14°. Near 
the top, on the south-west side, the angle is as high as 32° or 33°, but this is due 
to plastering on of sand and dust during the first rains while these materials 
were still being ejected. ‘The avalanches that swept the side of the cone not 
only carried down the new ejecta, but peeled and ploughed off a good deal of 
material that was there previous to the eruption, which is easily capable of 
verification on the spot. This included most of the railway, which has been 
completely stripped from the mountain side with the rails, massive sleepers, 
and concrete bedding (figs. 4 and 5, Pl. VIII.). The same fact is strikingly 
obvious in comparing the outline of the mountain of 1903 with that of 1907. 
SUBSIDIARY PHENOMENA. 
Several observers state that part of the Vesuvian coast was raised, and Prof. 
Mercalli, aided by Prof. Ambrosini and Dr. Limanowski, collected observations 
which seem to indicate that an elevation of the coast-line extending from Vico 
Equense to Portici occurred during the eruptive period, and that the change of level 
amounted to from 0°30 to 0-40 m. Unfortunately, my recommendation of years 
ago, subsequently repeated by Prof. Mercalli, that bradysysmic and mareographic 
observations should be made all over this region, has never been carried out. 
If this had been done, this elevation of the voleano might have been accurately 
recorded. This elevatory effect has been observed in at least a dozen paroxysms 
of Vesuvius, and in that of 1861 was very evident. In fact, it is just possible that 
such changes of level may precede a great eruption, and in that case would be 
the much sought-for premonitory warning, and, therefore, of inestimable value. 
During the fall of dust and lapilli, the discharges of electricity were, as is usual 
in such eruptions, very frequent and brilliant, but presented no very striking 
characters, and seem to have attracted little study. Hardly any damage seems 
to have been done, for even during the terrible night of April 7-8th, at Ottajano, 
the telegraphic instruments were able to be worked. At Ottajano railway 
station the wires were fused at some spots, and the electric-bells were struck.* 
Around the base of such a volcano as Vesuvius, it not infrequently happens 
that the erosive and transporting power of rain is more to be feared than damage 
by falling ejecta. In my paper on the geology of MonteSomma and Vesuvius, t 
I treated rather fully the question of erosive action on volcanoes, as illustrated by 
Vesuvius, and detailed reference is there made to the destructive effects of heavy 
* Sabatini, ‘‘L’ Eruzione Vesuviana dell’ Aprile, 1906,” p. 22. Roma, 1907. 
t ‘‘ The Geology of Monte Somma and Vesuvius.’’—Quart. Journ. Geol. Soc., vol. xl., 1884. 
