320 KEPOBT — 1888. 



Report of the Committee, consisting of Mr. H. Bauerman, Mr. F» 

 W. KuDLEE, Mr. .T. J. H. Teall, and Dr. H. J. Johnston-Lavis, 

 appointed for the investigation of the Volcanic Phenomena of 

 Vesuvius and its neighbourhood. {Drawn up by Dr. H. J. 

 Johnston-Latis, F.G.S., Secretary.) 



The reporter is glad to be able to announce tbat since last year some 

 very interesting additions to our knowledge of this region have been made, 

 some of which have a very important bearing on general questions in 

 vnlcanology. 



Geological Map of Vesuvius and Monte Somma. — It is with a feeling of 

 relief that the reporter is able to lay before the British Association his 

 ■work in a completed state. The preparation of the last sheet gave equal 

 trouble with the other three of the south side of the mountain, the district 

 being covered with habitations and high garden walls. The mapping of 

 the dykes of the Atrio del Cavallo, which had been left from the other 

 sheets, was carried out during the month of June of this year, and required 

 residence near the Observatory. As far as space and a plan map of a very 

 steep section would allow, all the principal dykes have been marked in. 

 The reporter has numbered foi-ty of the more striking of them in large 

 figures, from one to four feet high, in white paint, which correspond to 

 similar numbers on the geological map. Specimens of the salband and 

 interior of all these have been collected, and will be subjected to suitable 

 investigations ; also notes regarding the characters as observed in the field, 

 together with thickness, &c., have been made. An examination of this 

 section has revealed at least half a dozen hollow dykes, similar to that 

 giving rise to the eruption of May 2, 1885, which the writer was able to 

 study the formation of and describe, and has since observed at Stromboli 

 and Vulcano. Amongst those of Monte Somma, one was observed full at 

 the lower part of the section, but hollow at the upper, showing that it had 

 just drained out to the level of the parasitic cone or lateral eruptive mouth 

 that had been formed. 



Most important, however, was a dyke near the western end of the 

 Atrio section, which can be seen to be a hollow dyke refilled, and the 

 second filling to have been in part drained out, leaving a lava tunnel. 



The object of numbering the dykes in white paint is to identify them 

 both on the map and in the field, and to serve as a guide to anyone who 

 may care to investigate them. Many years since E,. Mallet numbered 

 twenty-seven of them in red (not sufficiently conspicuous), but no signs 

 of such could be met with. It would be well worth the trouble to have 

 these numbers repainted every two years, which could be done by any 

 ship's painter for a few francs. 



State of Vesuvius. — During August 1887 the crater of 1885 had not 

 further increased. It, as mentioned in the last report, was divided into 

 two crateral depressions, the active being the easterly one. To its north 

 side there is still visible a remnant of the old 1881-2 rim, whilst its 

 southern was split by a deep gully, the remains of the old fissure above 

 the dyke that gave origin to the lava outpour of May 2, 1885. An 

 attempt was being made to build up a cone of eruption. During the whole 

 time since then this cone of eruption has been growing, and has now- 



