Vol. 60.] VOLCANIC ACTION* IX THE PHLEGR.EAX FIELDS. 297 



between the giants and the gods, terminating in the ultimate victory 

 of the latter. 



In the month of March 1903, I made some memorable excur- 

 sions in this region with Sir Archibald Geikie, who urged me to 

 give a summary of the results of my researches into its volcanic 

 history, which might be submitted to the Geological Society of 

 London. In now complying with this request, I am not unmindful 

 of the many errors and omissions to which the student of so 

 complicated an eruptive area is liable, an area wherein even- 

 new excursion propounds fresh problems and suggests unsuspected 

 mysteries. 



In order to trace this volcanic history with most satisfaction, it 

 is desirable, first of all, to understand the geological structure of 

 the great basin of the Bay of Xaples, in which the eruptions have 

 taken place. 



II. Origix of the Bay of Xaples. 



The same rocks as those which form the backbone of the Apennines 

 constitute also the fundamental skeleton of the Neapolitan area : 

 that is, Upper Triassic dolomites, Cretaceous dolomites and lime- 

 stones, Flysch (Eocene-Miocene) sandstones and marls. These 

 strata, the combined thickness of which is some 3300 feet, have 

 been dislocated and fissured by the post-Eocene orogenic uplift of 

 the Apennines. 1 While this upheaval contorted the softer deposits 

 of the Elysch iuto innumerable narrow folds, or left patches of 

 them imprisoned within and pinched into the fissures opened up in 

 the underlying Mesozoic formations, the rigidity of these last- 

 named rocks formed a sufficient obstacle to their plication into 

 tightly-packed folds. Consequently they were slightly curved into 

 broad domes and large basins, which in their turn were fractured 

 by dynamic agencies, and the dismembered masses slipped along 

 the fracture-planes, step-faults, etc. being thus originated. 



One of these fractured basins is precisely the great calcareous 

 hollow which, sweeping rouud from the Island of Capri and the 

 Peninsula of Sorrento past the hills of Xola, Caserta, and Capua, 

 and projecting again into the sea at Massico, embraces, as within 

 one colossal amphitheatre, the entire Campania Felice. In Capri 

 and Sorrento the strata dip north-westward, at Caserta westward, 

 and at the Monte Massico south-westward. Thus they form a 

 synclinal depression, the major axis of which, trending north-west 

 and south-east, is some 43^ miles long. The entire rim of this 

 great basin is broken by huge longitudinal fractures, striking 

 sensibly parallel with the Apennines (from north-west to south- 

 east) ; and by transverse fractures perpendicular to the first- 

 mentioned, and therefore trending south-west and north-east. 



But the present configuration of the Apennine country is no 

 longer such as it was broadly outlined by the post-Eocene uplift. 



1 For this and the subsequent observations, see G. de Lorenzo ' Studii di 

 Geologia nell' Appennino meridionale ' Atti R. Accad. Sci. Xapoli, ser. 2, 

 vol. viii (1897) no. 7. 



Q. J. G. S. Xo. 239. x 



