338 EEPOET— 1 892. 



Report of the Gommittee, consisting of Messrs. H. Bauerman, 

 F. W. KuDLER, and J. J. H. Teall, and Dr. H. J. Johnston- 

 La vis, appointed for the investigation of the Volcanic Pheno- 

 mena of Vesuviios and its Neighbourhood. {Drawn up by 

 Dr. Johnston-La VIS.) 



Since the last report nearly all the tunnelling for the great main sewer 

 is complete, and few additional facts of interest have come to light. 

 Several little problems of purely local geology have, however, been solved. 

 In the lower sewer collector, beneath the tramway tunnel of Naples, a pecu- 

 liar grey trachy tic mass has been met with, and was penetrated for a short 

 distance. On account of a lawsnit the works do not progress. The mass, 

 however, is of considerable interest, as it is below the great yellow tuff of 

 Posilipo and Naples. The rock was ejected rapidly in very pasty or almost 

 solid fragments, which in some cases blended with the others thrown out 

 just befoi'e and after, and are flattened out in a pipernoid manner. At 

 other points the fragments are broken, mixed with dust, and consequently 

 incoherent. When this deposit is cut through, it will probably confirm 

 my theory regarding the piperno of Pianura and Soccavo, as being the 

 result of lumps of lava ejected in great blobs, which falling quite hot around 

 the vent have become resoldered together, and have even flowed a little. 



Very high temperatures have been met with in the tunnel near the 

 Solfatara, where I registered myself 59° C. on a day that the workmen 

 considered a very fresh one for the workings, i.e., with a high barometer 

 still rising. 



The statement made many years since by Professor A. Scacchi, that 

 fragments of leucitic lavas had been found by him at the Foce di Fusaro, 

 near the Torre Gavetta, led me to suspect the existence there of the 

 Museum breccia. On examining the locality this was confirmed, and, in 

 fact, the whole sea cliff" of Mte. di Procida exhibits a most interesting 

 though complex section of the volcanic series of the Phlegraean Fields. 



We have there a sei'ies of trachytes forming the base of the section, 

 very various in texture, and often covered with thick beds of their own 

 scoriae, which are often consolidated into a kind of trachytic breccia quite 

 analogous to the ' sperrone ' of the Alban hills. This is overlaid by fine 

 lapilli and pumice beds, which vary very much in thickness. Lying un- 

 conformably upon these are irregular buried outliers of the grey pipernoid 

 tuff of the region. In one place the pipernoid tuff is seen in section as 

 an exceedingly obtuse V-shaped mass, having choked an old valley, and 

 possessing the following characters : The black scoria fragments are very 

 slightly, if at all, flattened, are very spongy, are of good size, and form an 

 important constituent of the deposit. From this we can conclude that 

 the distance would well correspond with my supposed eruptive month 

 to the S.S.W. of Camaldoli, not very far from the Lago d'Agnano, from 

 which I believe issued the piperno and the greater part of the pipernoid 

 tuff of the Campania. The distance was, in fact, such as to allow time for 

 only the lighter pieces of scorise, the equivalent to the black flackers of the 

 piperno, to travel so far, and these to be so cooled that when they fell they 

 were too rigid to be flattened out by the impact. 



This grey pipernoid tuff has here suffered much denudation, for in 



