312 PROF. G. DE LORENZO OX THE HISTORY OF [Aug. I904, 



broken down and swept away the southern wall of the crater, 

 only the northern part remaining as a crescent -shaped ridge. 

 Little tufaceous hillocks, like that of Santa Teresa, occur at other 

 localities in the Phlegraean Fields, as, tor example, the Hill of the 

 Crisci, between Cigliano and Campana. But they have been so 

 greatly denuded that it is no longer possible to determine whether 

 they are the outcome of single eruptive outbursts, or represent 

 remnants left from the erosion of neighbouring craters. 



Volcanic deposits of the same type as those of the Campana craters, 

 that is, made up chiefly of red and black scoriae and bombs, inter- 

 mingled with fragments of pinkish-yellow tuff, are found dispersedly 

 in the Phlegraean Fields. They invariably overlie the yellow tuff, and 

 underlie the series of grey ashes, lapilli, and tuffs. These deposits 

 are typically massed on the western and northern slopes of the 

 Gauro volcano, forming the so-called Concola and the little 

 volcano of Fondo Riccio. They constitute also the great fan 

 of red and black scoriae which occurs on the Cleft Mountain 

 or Montagna Spaccata, where the ancient Via Campana runs 

 through a deep cutting into the Piano di Quarto. Again, they are 

 found north-east of the city of Naples, on the eastern slopes of 

 Capodimonte, and at Santa Maria del Pianto and the 

 Ponti Rossi. Yet although, as I have already pointed out, these 

 deposits are lithologically very similar indeed to those of the 

 Campana craters, they must be of much greater age, as is indicated 

 by their structure and by their invariable infraposition below the 

 grey tuff. At La Concola and the Fondo liiccio, the form of the 

 crater from which the}- were derived may still be traced ; on the 

 other hand, not a vestige of it remains among the scoriaceous masses 

 of Santa Maria del Pianto and the Ponti Rossi. The scoriae of the 

 Montagna Spaccata must have been either contemporaneous with, or 

 of but little later date than, the explosions which gave rise to the 

 great basin that lies east of Monte Gauro, which was possibly 

 anterior to the crater of Astroni and to that of Agnano. 



It is no easy matter, however, to determine the precise strati- 

 graphical and chronological relations either of these scoriaceous 

 volcanoes, or of the tuff-volcanoes which range in a direct north- 

 and-south line, west of Monte Gauro and Monte Nuovo, from 

 Monte Ruscello to Bacoli. 



The northernmost eminence along this line, Monte Ruscello, 

 is followed southward by a crater-ring known as Monte Grill o, 

 which encircles the later explosive crater of Avernus, this again 

 engirdling Monte Nuovo, the latest volcano of the series and of 

 the entire Phlegraean Fields. South of Baia is yet another little 

 crater of grey tuff, known as Fondi di Baia. 



Naturally, the most important of the whole of this series is the 

 crater-lake of Avernus, not only because of its dimensions and 

 depth, but because, alone among the volcanoes of the Phlegraean 

 area, it erupted, besides the customary ashes, lapilli, pumice, 

 scoriae, and blocks of the underlying yellow tuff, small scoriae of 



