Notices of Memoirs — Dr. Johnston- Lavis on Vesuvius. 511 



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 inconsiderable 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 con- 

 sequence of all this was that at the foot of the great cone in the 

 Atrio, during the year from 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 

 thickening away in all directions, but even under the escarpment 

 of Somma, the present floor stands for considerable distances over 

 5 ra. higher. In. consequence 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 were 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 will be seen of maintaining this numbering 

 intact. 



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 18^2, the outflow was much accentuated. During 

 January and February few variations were observable, but on 

 March 17 and 18 slight reflection from the crater was visible for 

 the first time for nearly a year, showing the rise of the lava in the 

 chimney, due certainly in part from blocking of the lateral channel 

 as the outflow of lava below was markedly diminished. On the 

 21st the activity at the crater was distinctly at the first degree, but 

 on the 22nd the second degree was attained. On that evening, how- 

 ever, a gush of lava showed the removal of the lateral obstruction to 

 its outflow, and the central activity so diminished that the following 

 night no reflection was visible. On March 29 and 31 the crater 

 again showed the first degree of activity. 



This was followed during the first week of April by a fresh out- 

 flow of lava, which still more increased during the next week. 

 During the first four days of the month feeble reflection was from 

 time to time visible from the crater. On the 12th, black dusty 

 smoke was puffed out from time to time. On visiting the Atrio, I 



