296 PROP. G. DE LOKENZO ON THE HISTORY OF [Aug. 1904, 



19. The History of Volcanic Action in the Phlegr^an Fields. 

 By Prof. Giuseppe de Lorenzo, of the Royal University of 

 Naples. 1 (Communicated by Sir Archibald Geikie, Sc.D., 

 Sec.R.S., V.P.G.S. Read April 13th, 1904.) 



[Plates XXVI-XXVIII: Maps & Sections.] 



Contents. 



Page 



I. Introduction 296 



II. Origin of the Bay of Naples 297 



III. The Eruptions in the Phlegreean Fields 300 



IV. Conclusions 31 4 



I. Introduction. 



The scene that discloses itself to the obseryer who enters the Bay 

 of Naples by the so-called Bocca Grande, presents three parts, 

 each characterized by distinct features. On the right, masses of 

 calcareous pink and white rock rise up into the Island of Capri 

 from the foam-flecked waters of the Mediterranean, and stretch 

 through Sorrento and Amain" to the cloud-capped Apennine. On the 

 left, a vast succession of undulating ridges of tawny-coloured tuff 

 begins, first at the Island of Ischia, and then, extending through 

 Vivara and Procida, spreads out into the gentle declivities upon 

 which Naples is built. In the central background looms grand 

 and solemn the smoking peak of Yesuvius. 



Just as these three components of the landscape are diverse in 

 aspect, so too are they diverse in geological origin and constitution. 

 The island of Capri and the peninsula of Sorrento are made up of a 

 gigantic pile of dolomitic and calcareous deposits of Upper Triassic 

 (Hauptdolomit) and of Cretaceous (Urgonian - Turonian) age. 

 Upon these rest in places a few insignificant patches of Eocene- 

 Miocene Flysch. Yesuvius is a typical volcano of concentric 

 accumulation (vulcano a recinto), almost entirely built up of 

 leucotephritie, fragmental, and laya-form materials. Between 

 Naples and Ischia lies a vast and complex assemblage of extinct 

 craters, which have erupted much fragmental material but little 

 lava, generally of a trachy-andesitic character, though excep- 

 tionally the crater of Vivara has disgorged a basaltic magma. 2 



This region, more especially that portion of it lying between 

 Naples, Cuma, and Miseno, received from the earl}* Greek colonists 

 the name of the Phlegraean Fields. These men, as they beheld 

 the titanic warfare between the subterranean volcanic forces and 

 the calmer agencies of the atmosphere, pictured it as a great battle 



1 Translated by the Assistant-Secretary. 



2 G. de Lorenzo & C. Riva ' II Cratere di Vivara nelle Isole Flegree ' Atti 

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



