Vol, 60.] VOLCANIC ACTION IS THE PHLEGR-EAN FIELDS. 315 



EXPLANATION OF PLATES XXVI-XXVIII. 



[Altitudes and soundings are expressed in metres.] 

 Plate XXVI. 

 Geological sketch-map of the Bay of Xaples, on the scale of 1 : 500.000. 



Plate XXVII. 



Sections across the B ay of Xaples, on the scale of 1 : 500,000 : and sections 

 across the Phlegrrean Fields, on the scale of 1 : 100,000. 



Plate XXVIII. 

 Geological sketch-map of the Phlegrrean Fields, on the scale of 1 : 100.000. 



Discussion. 



The President said that he was glad to tind that, owing to the 

 application of modern methods of research, as carried out in this 

 paper, and notwithstanding the increase of our knowledge oi 

 vulcanicity derived from such eruptions as those of Ivrakatoa and 

 Tarawera. these only supplemented and did not supersede the 

 teachings of the classical areas of the Mediterranean, including the 

 Phlegrteau Fields. It was a graceful act of the Author to send his 

 paper to the Geological .Society of a country, the geologists of 

 which — notably Sir William Hamilton and Sir Charles Lyell — had 

 contributed, so much to our knowledge of the Phlegraean Fields. 



Sir Archibald Getkie stated that, during the spring of last year, 

 he had had an opportunity of making a number of traverses of the 

 Phlegrasan Fields with the Author, and had been so much impressed 

 with the minuteness and breadth of his knowledge of the volcanic 

 history of the district, that he urged him to prepare a succinct 

 statement of this history which could be communicated to the 

 Geological Society. The paper read this evening was the result of 

 this request. It was a grievous loss to science when Prof. Carlo 

 Eiva, who had been associated with the Author in the preparation 

 of two admirable detailed memoirs on portions of the Phlegra?an 

 Fields, met his tragic death two years ago. But it was hoped that 

 Prof. De Lorenzo would himself continue the work which had been 

 so auspiciously begun. The speaker pointed out the interesting 

 similarity, between the sequence of volcanic events in the Xeapolitan, 

 and that in the Roman Campagna. In the latter area, the earliest 

 eruptions, as shown by the remarkable sections laid open by the 

 side of the Tiber to the north of Rome, took place in the Pliocene 

 sea, probably from many submarine vents ; while the latest were 

 all subaerial, and piled up the huge cones of the Alban Sill and 

 Bracciano. While rambling over the Roman Campagna, he (the 

 speaker) had not been able to trace out three periods of volcanic 

 activity, and had not found any satisfactory equivalent of the yellow 

 tuff which makes so conspicuous a feature in the Xeapolitan region. 

 Two periods of eruption, however, submarine and subaerial, were 

 well-developed, and possibly more detailed investigation and com- 

 parison might show the parallelism between the two areas to be 

 even closer than it appeared. 



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