I 



ON THE \OLCANIC PHENOMENA OF VESUVIUS. 321 



reached nearly to the level of the crater edge (June 10, 1888). The 

 activity of the volcano has been most constant, generally ranging from 

 first to second degree, and never exceeding the third. Lava, as in my 

 last report, has continued to flow without cessation, varying slightlv in 

 quantity. It has been chiefly occupied in oozing forth in difl'erent parts 

 of the Val d'Inferno, which it has further choked by piling up hills of 

 no considerable volume. 



An examination of the materials withdrawn from Russo's well at 

 Ponticelli, mentioned in last year's report, is not yet complete. It will be 

 remembered that after descending nearly 50m. below sea-level, leucitic 

 lavas were met with, with a thickness of over 50m. Beneath these lavas, 

 from 105-44m. to 107- 50m., beautiful rounded pebbles and sand are met 

 with. These consist of rounded fragments of a trachyte which strikingly 

 resembles that of the larger mass met with in the tunnel of the Cumana 

 railway at Naples. More important, however, were beautiful black 

 pebbles of a typical basalt, indicating that either from Vesuvius or the 

 neighbouring volcanic region this rock had been poured out at an early 

 date in the history of the eruptive activity of this region. 



This discovery is of still further importance in regard to theorising on 

 the sequence of rocks erupted in a given region, which will be further on 

 referred to. 



Excavations near Naples. 



Cumana Railway. — Geologists, engineers, and contractors, all believed 

 that the hills which back Naples, and are prolonged into the promontory 

 of Posilippo, consisted of a fairly uniform mass of yellow tuff". In last 

 year's report mention was made of large masses of trachyte being found 

 in the new railway tunnel, which is now near completion, and exhibifs 

 from beginning to end sections of deep interest, both local and general. 

 Investigations are being carried on continually from the stratigraphical, 

 lithological, pecrographical, and chemical aspects of the subject, but are not 

 yet complete, and therefore will only be referred to in general. Entering the 

 tunnel from Monte Santo, we meet with 530m. of tuffs, which are capable 

 of various subdivisions. From this point to 910m. one continuous raas» 

 of trachyte is met with, that is for near upon half a kilometre. Thi.^ 

 trachyte is in some places compact and very fine grained, in others soft 

 and spongy. At some spots thick beds of sodalitic fine-grained scoria 

 covering the surface may be seen, and in other places beds of blacker 

 scoria, as if near an eruptive oone, occupy a similar position. The sco- 

 riaceous surface continuous with the underlying compact trachyte mass 

 could be well seen at 730m. Unfortunately much is soon covered up by 

 masonry, so that frequent visits must be made to keep one thoroughly au 

 courant of the discoveries. 



This mass of trachyte is followed by yellow tuffs with variable coarse- 

 ness, compactness, and other characters, which graduate into a greenish 

 grey mottled with yellow tufi", and this eventually into a pure greenish 

 grey tuff". We have most distinct evidence of the gradual formation of a 

 yellow tuff from a compacted mass of fragments of pumice and scoria. 

 The process is distinctly due to the hydration of the glassy part of the 

 pumice and scoria. In many examples the surface of a block of pumico 

 has undergone this change, leaving an unaltered nucleus. The chemical 

 and microscopical changes involved in this process are undergoing investi- 

 gation, and will Boon be published in full. 

 1888. 



