308 PROF. G. DE LOEENZO OX THE HISTOEY OF [Aug. I904, 



were immediately succeeded by an uplift of the whole region, and 

 this by a somewhat lengthy period of erosion ; for the later 

 materials are everywhere, not only deposited (some- 

 times conformably, sometimes unconf ormably) upon 

 the eroded surface of the yellow tuff, but are evidently 

 derived on the whole from subaerial eruptions. 



Thus, we no longer find in these later deposits that uniformity 

 of composition which characterizes the yellow tuff, although they 

 also consist predominantly of fragmental materials of a trachy- 

 andesitic character. They show, however, both macroscopically 

 and microscopically, a certain diversity, according to the particular 

 eruptive vent from which any given material was derived. 



Moreover, we are no longer dealing with contemporaneous 

 eruptive vents, scattered, with some approach to regularity, over a 

 vast area, as was the case with the vents whence issued the 

 materials of the yellow tuff ; but we can trace a distinct succession, 

 both in time and space, with a progressive limitation and a slow 

 diminution of vulcanicity, all preluding the moribund stage or 

 perhaps final extinction of volcanic activity in the entire Phlegraean 

 area. 



In the succession of eruptive vents here, as is the general rule 

 with volcanoes, a primary big vent is followed by one or more of 

 progressively-diminishing size, a diminution accompanied by a 

 slight shifting of the axis of ernptivity. This shifting has been 

 sometimes confined within the circumference of the original crater- 

 rim, and we get as a result a system of concentric craters, or 

 crateri a recinto, as, for example : Agnano — Astroni — and the 

 internal craters of Astroni. At other times, the shifting has been 

 excentric, instead of concentric ; and this has resulted in a series 

 of parasitic cones on the outside of the first, as, for example, 

 Astroni — craters of Campana ; or Astroni — Cigliano. In other 

 cases, finally, the shifting of the axis of eruptivity has been so 

 considerable, as to leave no point of contact between the new and 

 the old volcano, and to give rise to entirely-different systems, as, 

 for example, Astroni and Monte Nuovo. I propose to enumerate 

 these different volcanic systems of the Third Period, beginning 

 with the oldest and ending with the most recent ; and, wherever 

 possible, to show an order of succession between widely-distant and 

 often mutually-independent eruptive vents. 



Around each such vent the generally-fragmental material was 

 heaped up in the same manner as that described in connection with 

 the yellow-tuff volcanoes. That is, crateriform girdles were built 

 up, wherein the layers dipped centrifugally outward, and in part 

 centripetally inward. The materials of these cones have a 

 generally greyish tinge, and are much looser in texture than those 

 which constitute the yellow tuff, from which they are therefore 

 easily distinguishable. On the other hand, it is not easy to 

 distinguish, one from the other, the products of the various volcanoes 

 of the Third Period. Consequently, at those localities which are at 



