140 Jounston-Lavis—The Eruption of Vesuvius in April, 1906. 
the level of the south-west edge of the 1872 crater-rim, and thus added to the 
mountain’s height. 
During the next ten years small eruptions, accompanied by outpourings of 
lava, first from one side and then from the other, gutted from time to time the 
cones of eruption, which were again rapidly repaired. Frequently, several con- 
centric crater-rings thus came into existence—on one occasion five such were 
figured and described by me. Durimg this period some thirty-seven papers, 
articles, reports, etc., of mine record the changes at Vesuvius from 1879 onwards, 
a list of which is published in the Bibliography of Vesuvius in my ‘‘ South 
Italian Volcanoes” (Furchheim: Naples, 1891). Two periods in this decade are 
interesting, as, although no very spasmodic or violent action was displayed, two 
large lava buttresses were constructed on the sides of the cone, constituting 
marked features in the outline of the mountain. These two buttresses also had, 
I believe, a marked influence in determining in part the point of overflow of two 
of the lava-streams of April, 1906. Early in 1883 lava reached the surface of 
the great cone in a 8. E. azimuth, and continued to flow in small quantities, often 
not reaching the Pedimentina. This dribbling may be compared to the guttering 
of a stearine candle when the grease flows first in a straight line, until by 
cooling it directs the further flow first to one side and then to the other, 
building up gradually a buttress that forms an important addition to the original 
mass. This lava-mass eventually developed into a bulky hump on the slope of the 
great cone of Vesuvius facing Torre Annunziata. (Fig. 10, Pl. X., right side.) 
Early in May, 1885, the great cone was again split down about one-third 
of its height, on the 8.8. W. azimuth, and a repetition of the same buttress- 
building took place as in 1883. It was in this eruption that I first discovered 
hollow dykes, and was able to study the mechanism of their formation.* These 
two humps on the back of Vesuvius are well seen in the photograph. (Fig. 10, 
Pl. X., left side.) ‘They limited the space of soft fragmentary material after- 
wards utilized by the zigzag path to Vesuvius, made by Sig. Fiorenza, and now 
destroyed by the last outburst. 
I have referred to these masses, as probably their size and cohesiveness 
prevented the outbursts of lava of the 4th April from reaching the surface at 
a higher level, as the cone had there a considerable crust of the 1885 lava, 
so that the new fluid rock had to find its way out, probably obliquely and farther 
to the south than would have been determined by the true azimuth of the dyke, 
were it not for this obstruction. It is probably in great part due to this 
arrangement that the large subsequent slipping occurred on the south slopes of 
the great cone, owing to the struggle of the lava to reach the point of least 
* H. J. J.-L.—“ L’Eruzione del Vesuvio nel 2 Maggio, 1885.”—Ann. d. Accad, O. Costa d. Asp. 
Naturalisti, Era 3, Vol. i., Napoli. 1886. Illust. 
