Vol. 60.] VOLCANIC ACTION IX THE PHLEGR.EAN FIELDS. 301 



under 2, is the representative of the Second Period ; and those 

 eruptive materials which are in situ, included under 1, mark the 

 Third Period. 



We will now examine how the materials belonging to these 

 three successive periods are visiblv represented in the Phlegraean 

 Fields. 



(1) First Period. 



The products of this period may be divided into two great 

 categories, corresponding to two different eruptive phases : the one, 

 more ancient, represented by the well-known piperno and the grey 

 pipernoid tuffs of Campania ; the other, made up of alternating 

 beds of pumice, lapilli, sands, breccias, and other volcanic accumula- 

 tions. It will be well to bear in mind the distinction between 

 these two categories. 



(a) Phase of the Piperno and Pipernoid Tuff. 



All the broad plain of Campania and all the valleys of the neigh- 

 bouring calcareous massif of the Apeninnes, from those of Capri 

 and Sorrento to the far-off vales of Salerno, Avellino, Caserta, and 

 Capua, are filled, to a greater or less thickness, with a grey trachytic 

 tuff, in which are scattered small black scorias, resembling in 

 appearance the well-known piperno, and consequently termed 

 ' pipernoid tuff.' In its present situation this pipernoid tuff is the 

 outcome of the heaping-up and consolidation, not only of detrital 

 eruptive material, transported by aerial, and perhaps also marine, 

 currents far from the original vents and laid down where it now 

 lies, but likewise of such material as was, both contemporaneously 

 and subsequently, washed down from the mountain-tops by running 

 waters and accumulated in the valleys. 



The detrital constituents of which these tuffs are made up (capable 

 of being carried by high winds 30 miles or more away from their 

 original source), must have been so rich in hydrofluoric, hydrochloric, 

 and sulphuric acids, that, helped by the action of percolating waters, 

 they acted upon the limestones against which they rested, and upon 

 such limestone-blocks as were embedded in the tuffs, inducing 

 extreme metamorphism therein, and thus originating the famous 

 fluor-bearing blocks which have been studied by A. Scacchi. 1 



These tuffs, as the well-sections and the natural exposures demon- 

 strate, rest almost directly upon the sedimentary rocks of the 

 Campanian basin, and consequently represent the first products of 

 eruption of that part of Campania. They were ejected from 

 volcanoes and craters, which have been completely obliterated by 

 later geological vicissitudes, but must have been at one time 

 concentrated especially in the area of the Phlegrrean Fields. 



1 See, in this connexion, Report of the Committee appointed for the Investi- 

 gation of the Volcanic Phenomena of Vesuvius & its Neighbourhood, drawn 

 up by H. J. Johnston-Lavis, Rep. Brit. Assoc. Adv. Sci. 1890 (Leeds) p. 397. 

 Also W. Deecke ' Zur Geologie von Unteritalien : § 3. Der sogenannte Cam- 

 panische Tuff Neuea Jahrb. vol. ii (1891) p. 286. 



