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



found the lava that flowed had formed the mound above spoken of, 

 surmounted by the fumaroles figured. 



During the night of May 3-4 fresh portions of the crater vp'all 

 collapsed and blocked the vent, so' that during the following day 

 hardly any vapour crowned the summit of the volcano. By the next 

 day the increased tension of the vapour was sufficient for it to force 

 its way through the obstruction, and much black sandy smoke 

 escaped during the 5th, 6th, 7th, and 8th. Obstructing masses that 

 l)ad detached themselves from the crater sides again plugged the 

 vent on the 27th and 28th, followed the next day by dark, sandy, 

 and dusty smoke. 



The flowing lava showed few new phenomena, with the exception 

 of the fine examples of conical and tubular spiracles formed above 

 the lava exit at the same locality, but above one set figured in the 

 last report that ai'o now buried. One of these is unique on account 

 of its curved overhanging form. It has been ejected at the highest 

 point of the new lava, and quite at the foot of the great Vesuvian 

 cone. I can only explain its inclination at the lower part, other 

 than that the escape of vapour and lava fragment were projected 

 upwards and outwards in a plane radial to the volcanic chimney 

 which corresponds with the orientation of the fumarole. This lateral 

 projection seems to have gone on for some time, so that many of the 

 blobs of lava blown out, fell and formed a support for the inclined 

 tube. As the blasts escaped more feebly the edges of the mouth 

 became more solid, and so the lower lip diverted the column more 

 in an upright direction, until the growth became almost vertical. 

 The whole effect is to produce a large mass somewhat resembling 

 a recumbent animal with its neck and head erect. 



About twenty yards more distant from the foot of the cone was 

 another large, obtuse, conical-shaped fumarole, which had been 

 broken away on one side and well exhibited the dome-like interior 

 covered by stalactitic lava. These constitute very fine examples 

 of what kind of spiracles may be built up on the surface of a coarsely 

 crystalline lava, such as that now issuing from Vesuvius. They 

 differ very considei'ably fi'om those desciibed and illustrated by 

 Dana and others from Hawaii, as also those formed on acid lavas at 

 Reunion, of which one or two figures have been published. 



At the time of visiting these fumaroles I was accompanied by my 

 friend Dr. E. D. Roberts, of London, who was much interested in 

 these striking formations. He is a man of average height, so that 

 the dimensions of these fumaroles can be judged of by comparison 

 with his figure by their side (photographs exhibited). 



At the summit of the great cone few changes have occurred beyond 

 the further enlargement of the crater. When slips took place from 

 the edges, dark dust-laden vapour was puffed out from time to time. 

 On one or two occasions the lava rose sufficiently high in the 

 chimney, combined with the sufficiently strong explosions, to project 

 a few lava cakes beyond the crater edges. The bottom of the crater 

 has been invisible from the large amount of vapour present on each 

 occasion that I visited the mountain summit. The extreme trunca- 



