282 Rejwrtu ami Froceedings — Geoloyical Society of London. 



disposition of the chief lines of fracture by which the Triassic, 

 Cretaceous, and older Tertiary formations were traversed previous 

 to the commencement of volcanic activity in this part of Italy. 

 He recognizes three chief periods in the volcanic history of the 

 district. 



I. The eruptions of the first series took place under the sea during 

 the Pleistocene period. Their surviving products can be grouped 

 in two distinct divisions, each recording a different eruptive phase. 

 The older of these (a) is represented by the piperno and grey 

 pipernoid tuffs of the Campania, which extend under the broad 

 plain into the valleys of the Apennines. These deposits consist of 

 grey trachytic tuff, with scattered black scorias, and with a varying 

 proportion of non-volcanic sediment washed down from the hills. 

 The vents whence they were ejected are now no longer to be traced, 

 as they have been obliterated or covered up by later accumulations. 

 The piperno, well developed at the foot of the hill of Camaldoli, 

 has given rise to some difference of opinion as to its nature and 

 origin. The author is disposed to regard it as a trachytic lava with 

 echlieren, the dark lenticles being made up of such minerals as 

 augite, aegerine, and magnetite, while the lighter matrix is felspathic 

 (anorthose) with a spherulitic structure and microlites of segerine 

 and augite. 



The second phase (h) of the first eruptive period is represented 

 by ashes, lapilli, pumice, and sands, intercalated with marine shell- 

 bearing clays and mails, and also with conglomerates and breccias, 

 these coarser kinds of detritus overlying them and varying in 

 thickness according to their proximity to or distance from the 

 vents whence the materials were ejected. The accumulations of 

 this epoch were pierced through in the artesian boring at the Eoyal 

 Gardens, Naples, where they were 330 feet thick. 



II. Above the records of the first volcanic period lie those of the 

 second — the yellow tuff, which forms the most wide-spread and 

 most characteristic of all the volcanic formations of the Phlegrsean 

 Fields. It is a yellow or cream-coloured, compact, well-stratified 

 aggregate of trachytic detritus, through which are scattered fragments 

 of tuff and lava. Its average thickness exceeds 300 feet. That it 

 was a submarine accumulation is shown by the occurrence in it 

 of oysters, pectens, and other organisms. Owing to the general 

 uniformity of its litliological characters, the yellow tuff has not 

 furnished any satisfactoi'y evidence of a definite order of succession 

 in the eruptions to which it was due. In spite of prolonged 

 denudation and of successive later volcanic vicissitudes, it is still 

 possible to recognize some of the separate vents from which the 

 tuff was discharged, such as the islet of Nisida, the hills of Posillipo, 

 Vomero, Capodimonte, and Camaldoli and Gauro. 



III. After the discharge of the yellow tuff from numerous cones 

 and craters scattered over the sea-floor where the Campi Phlegraei 

 now extend, the volcanic tract appears to have been upraised into 

 land, and to have been thereafter exposed to a prolonged period of 

 subaerial denudation. But the volcanic activity was not extinct, for 



