Notices of Memoirs — Br. Johnston- Lavis on Vesuvius. 507 



the mineral is distinctly crystalline, and, in my opinion, a purely 

 mechanical origin can scarcely be entertained. It appears to be 

 a chemical precipitate which has resulted in imperfect or disguised 

 crystallization. The floor crystallizations, known as " crystal cities," 

 at the Jenolan Caves, N.S.W., have a somewhat similar external 

 form. The mineral might have been formed in the drying up of 

 the calcareous waters of a lake. 



Papers and Ebpokts Eead before the British Association, Edinburgh, 



August, 1892. 



II.— Report of the Committee, consisting of Messrs. H. Bauekman, 

 F. W. EuDLEK, and J. J. H. Teall, and Dr. Johnston-Lavis, 

 appointed for the investigation of the Volcanic Phenomena of 

 Vesuvius and its Neighbourhood. (Drawn up by Dr. Johnston- 

 Lavis.) 



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 peculiar grey trachytic mass has been 

 met with, and was penetrated for a short distance. On account of 

 a lawsuit the works do not progress. The mass, however, is of 

 considerable interest, as it is below the great yellow tuif of Posillipo 

 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 before 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 T registered myself 59° G. 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 Phlegrean Fields. 



We there have a series of trachytes forming the base of the 

 section, very various in texture, and often covered with thick beds 

 of their own scorige, 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 unconformably upon these are 

 irregular buried outliers of the grey pipernoid tuif of the region. 



