300 PEOF. G. DE LOEENZO ON THE HISTOEY OP [Aug. 1 904, 



persistent chimney, in the Phlegrsean Fields, on the other hand, a 

 long series of outpourings and explosions took place from many 

 different funnels and vents. It is the object of the present paper 

 to show that in the latter case these phenomena followed a definite 

 order of succession, both in space and in time. 



III. The Eetjptions in the Phlegbjean Fields. 



Taking account of its aspect and its lithological characters, as 

 also of its stratigraphical succession, the eruptive material of the 

 Phlegrsean Fields may be divided into three principal categories, 

 which in their turn include evidence of several secondary eruptive 

 phases. The middle division of the three, and the most easily 

 distinguishable, is represented by the well-known characteristic 

 yellow tuff of Posillipo, which forms the main framework of 

 the entire Phlegraean area. The lower division consists of all the 

 various materials which underlie the yellow tuff, and are visible 

 only to a very small extent. Lastly, the upper division comprises 

 all the deposits of later formation than the yellow tuff. This 

 threefold distinction, of petrographical and stratigraphical relations 

 in the series of volcanic rocks in the Phlegraean Fields, points to 

 three main epochs of volcanic activity. It is needless to add that 

 at no single point is the series to be found complete and in the 

 exact order of superposition. Just as the eruptive vents varied in 

 their output, and the subsequent activity of denuding agencies 

 varied also : so too, both in quality and quantity, the representative 

 products of each particular period are seen to be diverse. "We may 

 consider, however, that a nearly complete type-section is available 

 in the artesian well of the lloyal Garden at Naples, sunk in 1847 

 at an altitude of 79 feet above sea-level, and going down to a 

 depth of 701 \ feet below sea-level, traversing therefore a thickness 

 of 780 | feet of deposits. The section, neglecting minor details, is, 

 in descending order, as follows : — 



Feet. 



1, Humus, drift-material, pozzolana, and grey lapilli ... 64 



2. Compact yellow and greenish tuff' 264 



o. Pozzolana, sands, sandy tuffs, pumice, volcanic breccias 



and conglomerates, intermingled with clays and marls 

 made up also of volcanic constituents of a tracbytic 

 facies 319 



4. Pipernoid grey tuff, similar to that of Sorrento and 



Caserta 88 



5. Pleistocene clayey sands, with marine shells similar to 



species now living in the Bay of Naples 45=j 



780| 



Of the formations enumerated in the foregoing section, those 

 included in Xo. 5 most probably represent the sedimentary platform 

 upon which rest all the eruptive deposits of Campania. The 

 various and complex constituents of 3 and 4 are records of the First 

 eruptive Period, anterior to the yellow tuff. This last, included 



