ON THE YOLCANIC PHENOMENA OF YESUVIDS. 341 



no essential ejecta, except on one side, where we have a mass of rock that 

 looks like a lava stream. It seems there must have been at the moment 

 of the ernption a very strong wind which carried all the lava fi-agments 

 in one direction, and as they fell they blended together into one fairly 

 uniform mass, the components of which are only faintly indicated by a 

 slight variation in colour, somewhat like piperno, but not so well marked. 

 The top and bottom are less coherent, for at the bottom the fragments fell 

 on cold ground, whilst the top, although falling on the hot mass beneath, 

 could not be pressed into contact with it by later falls. No doubt also 

 the explosions were feebler towards the end and the interval longer 

 between the fall of the last fragments. 



We find exactly the same thing in the piperno, namely, a spongy 

 tufaceous-like bottom and top. Besides this, the lulls and accentuations 

 of the explosive action are well marked, as well as the time that large 

 masses of the crater edges fell in and were re-ejected. At one time the 

 eruptive action seems to have been arrested, and the partly or entirely 

 consolidated plug was blown out into fragments and deposited amongst 

 the piperno. 



Vesuvius has since the last report, up to the time of my last visit in 

 May, shown very little variation. It will be remembered that lava was 

 issuing at the site of the eruption of June 7, 1891, at the foot of the great 

 cone, more than three hundred metres below the summit at the junction 

 with the Atrio del Cavallo, and nearly opposite the Punta del Nasone. 

 This outpour practically never stopped — at times it increased to no incon- 

 siderable quantities, but flowed only a short distance, on account of the low 

 gradient, tending to pile itself up into a mound. On other occasions it 

 seemed to become almost arrested, but it never practically stopped. The 

 consequence of all this was that at the foot of the great cone in the Atrio, 

 during the year ftom June 1891 to June 1892, a tremendous mound 

 or low-pitched buttress had been built up, so that its highest part I 

 estimate to be 20 m. above the old floor of the Atrio. This thickened 

 away in all directions, but even under the escarpment of Somma, the 

 present floor stands for considerable distances over 5 m. higher. In con- 

 sequence of this many of the dyke numbers which cost me so much 

 labour to put up some years since have been covered over. These I 

 hope to be able to replace this winter, and to repaint all the rest that are 

 now becoming obliterated. It will be remembered that these numbers 

 correspond with the dykes figured in my geological map of Vesuvius, and 

 all collectors now adopt these numbers to indicate the locality of the 

 dyke from which the specimens are obtained. Professor Bassani has 

 added a new and complete collection of these interesting dyke rocks to 

 the Naples Museum, and has arranged them according to my numbering. 

 The great importance of maintaining this numbering intact will be 

 seen. 



The actual details of the variations in the activity are as follows. 

 During the summer and autumn of 1891 more crumbling in of the crater 

 edges took place, followed by black sand and dust-charged vapour. The 

 outpour of lava from the base of the cone in the Atrio from time to time 

 almost stopped, to be followed again by fresh gushes. On the first day 

 of December a marked extension took place to the south and south-east of 

 the crater by the further crumbling in of its edges. On the last day of 

 the old year and commencement of 1892 the outflow was much accen- 

 tuated. During January and February few variations were observable, 



