Vol. 60.] VOLCANIC ACTION IX THE PHLEGR.EAN FIELDS. 303 



perhaps with the piper no and the pipernoid tuffs, they are the 

 products of submarine eruptions. 



The series consists of ashes, sands, lapilli, and trachytic pumice, 

 often intermingled with shell-bearing clays and marls, while inter- 

 calated among them and overlying them are conglomerates and 

 coarse breccias of a thickness which varies with their proximity to, 

 or distance from, the vents whence they were erupted. These 

 breccias, to which Dr. Johnston -Lavis has applied the name of 

 Museum Breccias, are made up of blocks of all sizes, torn indis- 

 criminately from the underlying rocks, and therefore of extremely 

 diverse character. Among them may be noticed, as especially 

 abundant, blocks of obsidian, pumice, and scoriaceous trachyte ; 

 hardly less numerous are the fragments of leucitic and of meta- 

 morphosed calcareous rocks. Taken as a whole, they bear a 

 remarkable resemblance to the breccias of the islands of Procida 

 and Vivara, 1 and date probably from the same period as these. 



In fact, we find these deposits of sandy and clayey tuff, of 

 conglomerates and breccias, sometimes intercalated with deposits 

 of rusty-black cinders or scoriae, most typically developed in that 

 part of the Phlegraean Fields which is nearest the above-mentioned 

 islands — that is, along the entire western base of the Monte di 

 Procida, and on the north-western flanks of the Monte di Cuma. 

 Another remarkable deposit is that which occurs below the 

 Camaldoli, in the shape of picturesque, precipitous, ruddy crags, 

 seen from afar off to be clearly based on the piper no and capped 

 by the yellow tuff. Noteworthy also is the great mass of these 

 strata, about 330 feet of which were pierced through in the 

 artesian boring of the Royal Garden at Naples. Finally, traces of 

 them have been met with below the Yomero Hill, in the course of 

 excavations made for the cable-railway from Montesanto to 

 Yomero. 



It need scarcely be added that exactly-similar deposits, overlying 

 the pipernoid tuff, are found in the valleys of Capri, Sorrento, and 

 other localities in Campania. But in this paper we are concerned 

 only with those which lie near their source of origin, in the 

 Phlegraean Fields. Here, indeed, they are exposed only at a few 

 points, being elsewhere mantled over by the eruptive masses of the 

 Second and Third Periods. 



(2) Second Period. 



Overlying the breccias and conglomerates of the Camaldoli, of 

 Monte di Cuma, and of Monte di Procida, are the masses of the most 

 widespread and most characteristic geological formation to be seen 

 in the Phlegraean Fields — the yellow tuff. This tuff, characterized 

 bv a fine cream-coloured or straw-coloured yellow tint, is a well- 

 compacted aggregate of ashes, lapilli, and small pumice-fragments 

 of trachytic nature. Scattered through this uniform matrix are 



1 G. de Lorenzo & C. Kiva ' I] Cratere di Yivara nelle Isole Flegree" Atti 

 E. Accad. Sci. Napoli, ser. '2. vol, x (1901) no. 8. 



