ON THE VOLCANIC PHENOMENA OF VESUTIUS. 315 



we bad not felt, altbougli tbey were described as the most seyere that 

 had been felt. 



Having ascended to the summit of Vesuvius, we found the central 

 crater rapidly enlarging by tbe falling in of its edges. From tbe new 

 fissure at its summit was issuing much vapour under pressure, and rich 

 in sulphurous acid, wbich is, even in traces, intolerable ; and the hot air 

 coming from innumerable new fi.ssnres rendered approach very difficult. 

 We did, in fact, once jump across part of the fissure, but retuined much 

 quicker on account of the hot irritant vapours. An approach from the 

 opposite side was equally unsuccessful. At some old f umaroles on tbe 

 1872 crater plain I collected some crusts of boric acid and alum, both 

 rare products at this volcano. 



I then wrote that one of three terminations we may expect to these 

 pbenomena, which are very characteristic of a lateral disruption, so 

 common at Vesuvius ' : — 



1. Should the lava cool sufBciently to plug the radial dyke, no further 

 phenomena will occur, and activity will be restored to the central vent. 



2. If this plugging only partially takes place, lava may dribble forth 

 for months, but probably the escape of vapour will soon be restored to 

 the central vent. 



3. If the rent should widen, considering how low it extends, we may 

 expect a grand eruption wbich might rival that of 1872, which com- 

 menced near the same spot and much in tbe same way ; the mechanism 

 by which this occurs I have explained elsewhere. ^ 



The suggestion that I published in several newspapers has been fully 

 confirmed — namely, that the second alternative type of eruptive character 

 Avould be pursued by the volcano. Now, for a period of nearly two 

 months lava has continued to dribble forth, activity has returned to the 

 central vent, and no great changes have occurred. 



The throat of the volcano commenced to be cleared on June 9, the 

 vapour forcing its way up from the crater bottom through the choke of 

 loose materials, and rose above as a column carrying with it much dust; 

 at the same time the powerful vapour blast issuing from the upper 

 extremity of the lateral rift soon stopped. Each day I was kept informed 

 of the state of the volcano by the kindness of Messrs. Ferber and Treiber, 

 the director and engineer respectively of the Vesuvian Railway. 



On June 15 1 considered it right to again visit the mountain, and had 

 the good fortune to be accompanied by Messrs. H. Elliot, A. Green, 

 Linden, Newstead, and Treiber, several of whom are excellent photo- 

 graphers, so that with two of my own cameras we were able to make an 

 extensive pictorial record of some very nnique formations. 



At the point of issue of the lava, at the junction of the foot of the 

 great Vesuvian cone and the Atrlo del Cavallo, the first lava had cooled 

 Bufficiently to walk over it, but beneath our feet could still be seen in a 

 few holes the flowing lava. At the foot of the great cone, and extending 

 for half-way across the Atrio, along the radius of the eruptive rent, as if 

 this had continued so far, were a series of driblet cone fumaroles. We 

 counted seven complete and well-formed examples, besides numerou.s 



' ^Mt7/re, vol. -kUv. Jnne 18, 1891, pp. 160-161; Cnrriere di Nopoli, June 10: 

 LIUtlie, June 11 : The ^Mediterranean Natvralist for July. 



^ H. J J. L., 'The Relationship of the Structure of Igneous EocIjs to the Con- 

 ditions of their Formation,' Scientific Proceedings Hoy. Lvhlin Soc , vol. v., N.S., 

 pp. 112-56. 



