306 PROF. G. DE LORENZO ON" THE HISTORY OF [Aug. I904, 



big black scoria?, as is always the case in the neighbourhood of the 

 eruptive vents, and is mantled with a thin covering of pozzolana 

 and grey tuff, the products of the later eruptions of the Third 

 Period. The volcano of Nisida, being the smallest and the best 

 preserved of all those that were built up of the yellow tuff, may be 

 regarded as a type and a model for pursuing the study of the 

 remainder. 



Practically joined to j^isida by small skerries of yellow tuff, the 

 fine hill of Posillipo towers above the sea with its perpendicular 

 walls some 500 feet high, and its long picturesque summit-ridge 

 stretching inward to Xaples. This hill, as has been shown else- 

 where, 1 represents the lateral remnants of two contiguous volcanoes, 

 the craters of which opened on the flats of Bagnoli and Fuorigrotta. 

 The western flanks of these volcanoes were demolished by later 

 eruptions (probably from Agnano), while their eastern slopes have 

 survived to form the ridge of Posillipo. In this ridge, the strata 

 of yellow tuff dip outward or towards the south-east. Its crest, 

 like that of every other Phlegra?an hill, is crowned with soft grey 

 tuffs and pozzolana, the varyingly- conformable and uncon- 

 formable superposition of which upon the yellow tuff may be well 

 observed in the great cuttings, and in the caves situated at Piedi- 

 grotta and at the outermost extremity of Posillipo, at Coroglio. 



Separated from that ridge by a gentle syncline, the hills of the 

 Yomero, Capodimoute, and Poggioreale rise on the north- 

 east : they, too, are fundamentally built up of yellow tuff. The 

 original forms of these volcanoes, however, are not easilv made out 

 in this case, as they have been masked by later eruptions and 

 demolitions. It may be that their craters corresponded more or less 

 to the existing curved shores of La Marinella and the Riviera di 

 Chiaja, and that they were divided one from the other by the crest 

 which even now (though in part demolished) projects from the 

 Yomero into the promontory of Ecchia or Pizzofalcone, and thence 

 into the rock-shelves and skerries of Castel dell' Ovo, which like- 

 wise consist of yellow tuff. Amid the yellow tuff of the Yomero. 

 the excavations made for the tunnels of the Cuman Railway and 

 for the great storm-water drain, have revealed a considerable mass 

 of trachyte, which bears witness to the probability of lava-erup- 

 tions, if not during that period, at least during the immediately- 

 preceding age. 



The neighbouring Hill of the Camaldoli (1502 feet high), 

 forming the most elevated summit of the Phlegraean Fields, is 

 manifestly made up, for the greater part, of yellow tuff. This is 

 seen on every hand below the loose grey tuffs and the pozzolana, 

 where these rocks have been laid open in the gullies and channels 

 which seam the northern flanks of the hill. The eruptive vents of 

 this yellow tuff were evidently situated in the two basins of Soccavo 

 and Pianura, which preserve to this day an unmistakable crateri- 

 form aspect. 



1 G. de Loreuzo & C. Riva ' II Cratere di Astroni nei Cauipi Flegrei ' 

 Atti R, Accad. Sri. Napoli, ser. 2, vol. xi (1902) no. 8, p. 72 & fig. 5. 



